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** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
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/* This work is registered directly with the copyright offices of the */
/* United States and of the United Kingdom, and indirectly in many other */
/* nations via the conventions the above are signatory to. */
/* Generous licensing terms are available on inquiry. */
I N T R O D U C T I O N
This book is a technical reference. It is NOT a tutorial. Hopefully, this
book is what you'll reach for when you want find out what Peter Norton or the
"official" references glossed over.
This manual is intended to replace the various (expensive) references needed
to program for the DOS environment, that stack of magazines threatening to take
over your work area, and those odd tables and charts you can never find when
you need them.
The various Microsoft and IBM publications and references don't always have
the same information. This has caused some consternation about the
"undocumented" features to be found in DOS. In general, if a call doesn't
appear in the IBM DOS Technical Reference it is considered "undocumented"
although it may be documented by other OEMs or by later Microsoft tech
bulletins.
The information here is valid for DOS 2.x through 5.x. Where there are
differences between the two versions there are notes in the text. No great
effort was expended on DOS 1.x.
When I started writing this book, it was originally for my own personal use.
Then I began expanding it with the idea of getting it published, since at that
time there was *nothing* in print like it. (late 1987) If I had managed to
send it off to the publishers early enough, I would have had it made. As it
was I lost six months having a nice steel rod put in my leg after being run
over by a drug addict in an uninsured car, and half a dozen similar books were
published by then, and nobody was interested in mine. Six months is a long
time in the PC world.
That's why I'm uploading this file as "user-supported." It gives me a chance
to recoup a few bucks for the time I've been working on this thing, and it
gives some advantages that a printed book can't - first, you can load it on
your hard disk and use Vern Buerg's LIST or SideKick to scan through text. You
can grab a piece of something and paste it into a document, etc. If you help
support the Reference you will always have the latest version available; you
can't "upgrade" books.
A project this size takes a LOT of time and effort. I've tried to verify as
much of the information I've received as I could, but there's just too much for
absolute certainty. The TechRef has been in the hands of some heavy-duty code
jockeys for a couple of years now with very few bug reports, though.
If you find any typos, incorrect information, or want to see something else,
let me know. If you have any more detailed information on something, PLEASE let
me know!
Dave Williams
D I S C L A I M E R
As is common these days, I have to make a "Notice of Disclaimer". I take no
responsibility for anything, and if anything you do with this book ruins you
for life or makes your dog bite you, or anything else, that's just tough.
I hope you find much use for this reference. It was a trip to write, too.
Dave Williams
(C) Copyright 1987, 1992
/* note: the above disclaimer is being used as an example in the University */
/* of Texas' School of Law. Whether good or bad, my respondent didn't */
/* say... */
______________________________________________________________________________
Copyrights and trademarks:
(3COM Corporation)
3COM, Etherlink
(Allied Telephone and Telegraph)
UNIX, AT&T
(Artisoft)
LANtastic
(AST Corporation)
AST, RAMpage!
(Atari Computer)
Atari, ST, TOS
(Borland)
Borland, Turbo C, Turbo Pascal, Turbo Lightning, Turbo Assembler, SideKick
(Commodore Business Machines)
Amiga 2000, Bridge Board
(Compaq Computer Corp.)
Compaq, Deskpro
(Cordata Computer)
Corona, Cordata
(Cove Software)
CED, PCED
(Digital Equipment Company)
DEC, Rainbow, DECMate, DOS (uh... yeah. DEC owns the trademark to 'DOS')
(Fox Research, Inc.)
10-Net
(Graphic Software Systems)
GSS, DGIS
(Hayes)
Smartmodem
(Hercules Computer Technology)
Hercules, HGC, Hercules Graphics Card Plus, InColor Card
(IBM Corp.)
IBM, PC, PCjr, PC/XT, PC/AT, XT/286, PS/2, TopView, Micro Channel, 3270 PC,
RT PC, Token Ring, OS/2
(Intel Corp.)
Intel, iAPX286, iAPX386, LIM EMS, Communicating Applications Standard (CAS)
(Logitech, Inc)
Logitech, Logimouse
(Microsoft Corp.)
Microsoft, MS, MS DOS, OS/2, Xenix, Windows, Windows/286, Windows/386,
Microsoft Networks, LIM EMS, XMA, DPMI
(Mouse Systems Corp.)
Mouse Systems, PCMouse
(Novell Development Corp.)
Novell, NetWare
(Phar Lap)
VCPI, Virtual Control Program Interface
(Qalitas)
386-To-The-Max, 386MAX
(Quarterdeck Office Systems)
DesQview, QEMM
(SEAware, Inc)
ARC
(Softlogic)
DoubleDOS
(Sunny Hill Software)
TaskView, OmniView
(Tandy Corp.)
Tandy, Radio Shack, DeskMate
(Texas Instruments)
TI, TI Professional, Business Professional, TIGA (TI Graphics Interface)
(Zenith Radio Corporation)
Zenith, Z-100, Z-248
(ZSoft Corporation)
ShowPartner, Paintbrush
"LIM 4.0" and "Expanded Memory Specification" are copyright Lotus Development
Corp, Intel Corp, and Microsoft Corp.
"EEMS", "AQA 3.1" and "Enhanced Expanded Memory Specification" are copyright
by Ashton-Tate, Quadram, and AST
"DPMI" and "DOS Protected Mode Interface" are copyright Lotus Development
Corp, Intel Corp, Microsoft Corp, and AST
Various other names are trademarks of their respective companies.
�袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴袴�
� Programmer's Technical Reference for MSDOS and the IBM PC SWv2.2a �
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This is a user-supported technical reference. If you find this information
to be of use, please mail your check or money order for US $20 + $1.75 S&H to:
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� PO Box 181 �
� Jacksonville, AR 72076-0181 �
� USA �
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Shipping is US Postal Service Air Mail. For non-Australian foreign orders,
see the file 'PAYMENT'. Site licensing and product licensing terms are
available.
If you wish to make payment in Australian dollars, please mail your check
or money order for AUS $29 or credit card information to to:
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� Spearwood Shareware Service �
� PO Box 121 �
� Hamilton Hill, WA 6163 �
� Australia �
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Spearwood Shareware Service is our authorized Australian dealer.
They will forward your order to the USA and you will receive the
absolute latest version of DOSREF by airmail straight from the
author. This means there will be about a three week delay before
your order arrives. We appreciate your business!
Spearwood is our dealer only; for support write or E-mail the
author, Dave Williams, at the above address.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Why support DOSREF instead of relying on one of those public domain
"interrupt lists"? Sheer size, for one. Even in LHarc format DOSREF
bulks out to over a megabyte, making it too large for most sysops to
consider keeping online. Registered users also get support via:
The Courts of Chaos BBS (TechRef support board)
RIME/RelayNet
BIX
CompuServe
airmail
You get the very latest edition of this manual on disk, with no worries
about corrupted or tampered text. DOSREF is a quality product, in use
by the US Navy, CalTech, Borland, NEC, Wang, General Motors, Citicorp,
Rockwell, Honeywell, Digital Research, Central Point Software, 20th Century
Fox, Associated Press, hospitals, universities, and government agencies
around the world.
The Registered User reference consists of over a megabyte of the compressed
technical reference, appendices, and sample source code. That's about three
megabytes of raw data when uncompressed, or several times larger than the
shareware version.
The Registered User version contains information on device drivers, mouse
programming, Virtual Control Program Interface, Microsoft Windows 2.x, hard
drives, hardware information, virus and Trojan programs, EMS 3.2, LIM 4.0,
EEMS 3.2, CD-ROM, network programming, DOS 5.0, and more.
Registered users will be advised by mail of updates.
Several people who have downloaded copies over three years old have written
to see if I was still supporting the Reference. The answer is yes. Not only
that, but my book contract calls for keeping the information current. If
you're concerned, just drop a postcard.
*****************************************************************************
Foreign langauge versions are available!
Klaus Overhage of Stuttgart, West Germany has licensed DOSref for
redistribution and is now able to provide versions in German. Klaus' version
is a separate product from this one and must be purchased separately. Klaus
is providing full support for German users. If you'd like a copy in German,
please contact:
Klaus Overhage
Rosenstrasse 15 A
7000 Stuttgart 50
Germany
I hope to have other languages available soon. If you are interested in
purchase or translation, please contact me for details.
*****************************************************************************
For payment in British pounds, Canadian dollars or EuroCheques, see
INVOICE.TRF and PAYMENT. I fully support foreign users! If you're having
trouble arranging payment, write (or leave EMail) and I'll try to work
something out.
Do you live outside the US? If so, you're probably familiar with the
hassles of keeping up with the latest information - the three to five month
lead time for US publication, plus time for local book dealers to catalog
new releases, plus problems in trying to order... plus the delays while your
book comes in on special order, goes through Customs, the inevitable price
hikes through all the middlemen, taxes... not only is DOSREF priced
well below the price of good printed computer books in the US, it's probably
far cheaper than you could expect to pay for US books locally. Plus your
order will show up in your very own mailbox by air mail.
*****************************************************************************
Printed copies of the Tech Ref are available for �16.95 or US$35.10 from
Sigma Press, marketed by John Wiley & Sons UK. Address orders to:
Programmer's Technical Reference
by Dave Williams
ISBN 185058-199-1
John Wiley & Sons
Baffins Lane
Chichester
West Sussex PO19 1UD
England
They accept checks, most credit cards, or purchase orders.
*****************************************************************************
The latest shareware version is always available on BIX the ibm.dos/listings
area, the GEnie IBM file area, or:
The Courts of Chaos, (501)985-0059, (support BBS) CompuCom 9600
The Cat House, (501)376-6909, (sysop: Joe Felix) CompuCom 9600
RelayNet node ->CHAOS
send mail in COMMON or MULTITSK (I'm the Conference Host for Multitask)
MetroNet node ->CHAOS
send mail in METRONET
The DRAKE BBS, (0522) 824379, (sysop: Paolo Masetti)
Langhirano, Italy FIDOnet 2:332/502
GroupMed, (206) 581-9088 (sysop: Ismail Arslangiray)
Tacoma WA, USA FIDOnet 1:138/120 2400bps, 1:138/116 9600bps USR HST
instant access, latest DOSREF is FREQable
*****************************************************************************
Shareware is try-before-you buy software. If you find this package to be of
use you should consider registering. Registered users get the complete
version, support, and updates.
If you received this copy of DOSREF from a shareware vendor the money you
paid was only for the diskette, not the software.
Dave Williams is a member of the User Supported Software Association (ussa).
ussa wants to make sure that the user supported software principle works for
you. If you are unable to resolve a software-related problem with a ussa
member by contacting the member directly, ussa may be able to help. The ussa
Mediator can help you resolve a dispute or problem with a ussa member, but
does not provide technical support for members' products. Please write to the
ussa Mediator at Box 1000, London SE17 2UA, England.
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쳇컴쩡캑 Approved
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ussa
How to use DOSREF
This reference changes so often that any attempt to format it for pagination
would be a tremendous waste of time. Simply printing the thing out and letting
the pagebreaks fall where they may is how most people do it. The neatest
solution is Vern Buerg's LIST.COM or SideKick's file view function. If your
editor has multiple-window support, you can open a small window into the
Reference and cut and paste into your source.
An efficient method of using the Reference is to concatenate all the chapters
together with the COPY command, ie COPY CONTENTS + CHAPTER.001 + CHAPTER.002 +
..... + CHAPTER.017 REF. (REF being the new file name for the concatenated
files.) With LIST.COM, the backslash (\) or F9 key will search for strings.
You can then dump pieces of text to a disk file or your printer.
If you work better with a printout than scanning with a file viewer, try
setting your printer to 132 columns. This allows a nice margin for writing
notes and eliminates the problem some printers have when printing 80
character wide text. Some of the text and charts in the reference are a full
80 columns wide; unfortunately some printers wrap automatically at 79 columns.
Some printers don't handle a combination of compressed print and graphics
characters very well either. You may have to use the PRTRFIX.COM program
provided on Disk 1 to squelch the graphics for printing.
I strongly recommend using a viewer instead of printing. If you *must* print
the Reference out, do it in stages so your printer does not overheat. Some
inexpensive printers will self-destruct after a couple of hours.
** Programmer's Technical Reference for MSDOS and the IBM PC **
Copyright (c) 1987, 1992 Dave Williams
This is a listing of some of the new stuff added to the Reference. I didn't
keep a version list until 2.0; lots of stuff gets added between version
numbers.
09/87 first shareware release of the reference
11/87 LIM 3.2 functions
01/88 LIM 4.0 spec
05/88 AST EEMS 3.2 spec
06/88 DesQview and TopView calls, NetBIOS calls
07/88 Intel CAS 1.0 spec
12/88 Microsoft XMA 2.0 standard
03/89 Microsoft Windows 1.03 API
04/89 porting between operating systems
04/89 video programming
04/89 more networking
04/89 mouse programming
04/89 table of contents at beginning of each chapter
06/89 major bugfixes and verification of data
09/89 Microsoft TSR Programming Guidelines 1.0 (provisional)
10/89 PharLap VCPI 1.0
10/89 LANtastic network API
10/89 PC-MOS/386 4.00 partial API
10/89 partial DesQview and TopView
10/89 further updates to MS Windows API
12/89 PCjr cartridge support in DOS
12/89 more info on European multitasking DOS 4.0
12/89 added some paint program formats
12/89 info on computer viruses and Trojan Horses
06/90 expanded sysid ID codes in Chapter 2
07/90 add Connor Peripheral drives to Appendix 6
07/90 add Imprimis drives to Appendix 6
08/90 Weitek x167 math coprocessor interfaces
10/90 info on Pelican/Kodak 5.5mb 5-1/4 floppy drives
10/90 added info in IBM PC LAN and Token Ring API
11/90 int 10h functions for EGALOAD font loader, LANtastic AI-LANBIOS 2Fh
calls, CopyIIPC board ports, UMB definition in Chap2, updated Appendix
11 (glossary), added new Appendix 21 (hotkey definitions), completely
reworked partition tables in Chapter 8
12/90 added more network functions from IBM PC LAN reference
Version 2.0 released!
01/91 EISA access ports, more Carbon Copy int 10h calls, more history of
DOS, changes to partition table info in Chapter 8, more info on
IRQ7/int17, more info on eDOS 4.0, Pelican I/O ports, CopyII board I/O
ports, added network info to int 21h calls, added DOS 1.x info to int
21h calls, added ARJ archive format to Appendix 15
02/91 added DHELP.BAT to DOSCMDS. Lots of new ravings in MISCSTUF. STB VGA
modes added to chap16, ADT SmartFAX function calls, 8250 UART coverage,
8237 DMA Controller coverage, NEC 765 floppy controller chip coverage,
more coverage on AT int 70h timer, more Novell calls, GriD ID bytes
and specific BIOS functions, Leading Edge Model M undocumented BIOS
1Ah functions, Versa-Spool interrupts, ZIPKEY int 0B3h calls
04/91 extensive additions of network card port addresses to Chapter 2
extensive additions to hard drive listings
05/91 added Appendix 22, Sound Blaster API
added Appendix 23, French-Canadian accented character chart
moved XMS spec from Chapter 5 to Chapter 10, since many people missed
it buried in the 2Fh calls.
added more Desqview programming information
06/91 removed obsolete TIFF information; Aldus will give the latest spec
to anyone who asks. Put TIFF hotline number in Appendix 20.
added CIS GIF file format, by permission of H&R Block and CIS.
added PCX file format, by permission of ZSoft.
added DOS 5 mods and new information to ASSIGN in Chapter 5.
07/91 received permission from VESA to redistribute VESA documents.
documented SWITCHAR no longer works in 5.0
int 2Fh/fn 4Ah DOS 5 HMA services (partial)
int 21h/fn 33h DOS 5 "real" DOS version call
more information on 21h/60h (TRUENAME) and networks, Win3
added 8250 info back to Chapter 15
moved CIS GIF file format to Appendix 24
hex chart
Version 2.1 released
08/91 added more DV info to int 10h/0FEh
added int 21h and int 2Fh calls for DOS 5.0 from MS 5.0 Tech Ref
moved DoubleDOS functions from Chapter 4 to Chapter 17
added how to detect VDISK, some DV info to chap3, 15h/87h
more info on chap3, 15h/83h and 86h, AT int70 timer functions
more into on Create Temporary File changes under MS and DR 5.0
more model ID bytes in chapter 2
noted potential problems with MSC int86() and ints 25h, 26h
added CheckIt parallel loopback tester pinout
greatly enhanced bibliography (50 new entries!)
more info on the history of the PCjr
included Raintree's nice information file on DOS4 and SHARE
IBM-to-Mac serial cable adapter pinouts
more on 2Fh/16h, DOS give-up-time (used by OS/2 2.0 and Win3 too)
port addresses on Logitech ScanMan board
Microsoft TSR Specification 1.0 as Appendix 26
AT&T 6300 BIOS Data Area problem, Chapter 2
more info on int 15h,fn 4Fh (OS Hook)
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The rest of the chapters aren't included in this shareware demonstration
package. Since the complete manual takes about 1000k even compressed in
LHarc format, something had to give somewhere.
Here's a sample of what you're missing:
DOS 5 information (mainly in registered chapters 4, and 5)
(Chapters 1, 2, and 3 are the same as the registered version, less additions
since this demo was released)
TABLE OF CONTENTS
INTRO Introduction, credits, copyrights
CHAPTER 1 DOS and the PC
Some History .......................................................... 1**1
What is DOS? .......................................................... 1**2
Other Operating Systems ............................................... 1**3
Specific Versions of MS/PC-DOS ........................................ 1**4
The Operating System Heirarchy ........................................ 1**5
DOS Structure ......................................................... 1**6
DOS Initialization .................................................... 1**7
CHAPTER 2 Low Memory and Absolute Addresses
Introduction .......................................................... 2**1
System Memory Map ..................................................... 2**2
A Brief Guide to Current Memory Terminology ........................... 2**3
PC Port Assignment .................................................... 2**4
Reserved Memory Locations ............................................. 2**5
Absolute Addresses .................................................... 2**6
The IBM PC System Interrupts (Overview) ............................... 2**7
Quick Chart of Interrupts 00h-0FFh .................................... 2**8
The IBM-PC System Interrupts 00h-0Fh (in detail) ...................... 2**9
CHAPTER 3 The IBM ROM BIOS
Calling the ROM BIOS .................................................. 3**1
Interrupt 10h Video Services ......................................... 3**2
Interrupt 11h Equipment Check ........................................ 3**3
Interrupt 12h Memory Size ............................................ 3**4
Interrupt 13h Disk Functions ......................................... 3**5
Interrupt 14h Initialize and Access Serial Port ...................... 3**6
FOSSIL Drivers ......................................... 3**7
Interrupt 15h Cassette I/O ........................................... 3**8
Interrupt 16h Keyboard I/O ........................................... 3**9
Interrupt 17h Printer ................................................ 3**10
Interrupt 18h ROM BASIC .............................................. 3**11
Interrupt 19h Bootstrap Loader ....................................... 3**12
Interrupt 1Ah Time of Day ............................................ 3**13
Interrupt 1Bh Control-Break .......................................... 3**14
Interrupt 1Ch Timer Tick ............................................. 3**15
Interrupt 1Dh Vector of Video Initialization Parameters .............. 3**16
Interrupt 1Eh Vector of Diskette Controller Parameters ............... 3**17
Interrupt 1Fh Ptr to Graphics Character Extensions (Graphics Set 2) .. 3**18
CHAPTER 4 DOS Function Requests
General Programming Guides ............................................ 4**1
DOS Registers ......................................................... 4**2
DOS Stacks ............................................................ 4**3
DOS Interrupts ........................................................ 4**4
Interrupt 20h (Terminate) ............................................. 4**5
DOS Services (quick list) ............................................. 4**6
Calling the DOS Services .............................................. 4**7
Version Specific Information .......................................... 4**8
Compatibility Problems With DOS 4.0+ .................................. 4**9
PCjr Cartridge Support ................................................ 4**10
eDOS 4.0 .............................................................. 4**11
DOS Services in Detail ................................................ 4**12
CHAPTER 5 Interrupts 22h through 0FFh
Interrupt 22h Terminate Address ..................................... 5**1
Interrupt 23h Ctrl-Break Exit Address ............................... 5**2
Interrupt 24h Critical Error Handler ................................ 5**3
Interrupt 25h Absolute Disk Read .................................... 5**4
Interrupt 26h Absolute Disk Write ................................... 5**5
Interrupt 27h Terminate And Stay Resident ........................... 5**6
Interrupt 28h (not documented by Microsoft) ......................... 5**7
Interrupt 29h (not documented by Microsoft) ......................... 5**8
Interrupt 2Ah Microsoft Networks - Session Layer Interrupt .......... 5**9
Interrupt 2Bh Unknown ............................................... 5**10
Interrupt 2Ch Unknown ............................................... 5**11
Interrupt 2Dh Unknown ............................................... 5**12
Interrupt 2Eh Alternate EXEC (DOS 2.0+) ............................. 5**13
Interrupt 2Fh Multiplex Interrupt ................................... 5**14
Interrupt 30h FAR jump instruction for CP/M-style calls ............. 5**15
Interrupt 31h Unknown ............................................... 5**16
Interrupt 32h Unknown ............................................... 5**17
Interrupt 33h Used by Microsoft Mouse Driver Function Calls ......... 5**18
Interrupt 34h Turbo C/Microsoft languages - Floating Point emulation 5**19
Interrupt 35h Turbo C/Microsoft languages - Floating Point emulation 5**20
Interrupt 36h Turbo C/Microsoft languages - Floating Point emulation 5**21
Interrupt 37h Turbo C/Microsoft languages - Floating Point emulation 5**22
Interrupt 38h Turbo C/Microsoft languages - Floating Point emulation 5**23
Interrupt 39h Turbo C/Microsoft languages - Floating Point emulation 5**24
Interrupt 3Ah Turbo C/Microsoft languages - Floating Point emulation 5**25
Interrupt 3Bh Turbo C/Microsoft languages - Floating Point emulation 5**26
Interrupt 3Ch Turbo C/Microsoft languages - Floating Point emulation 5**27
Interrupt 3Dh Turbo C/Microsoft languages - Floating Point emulation 5**28
Interrupt 3Eh Turbo C/Microsoft languages - Floating Point emulation 5**29
Interrupt 3Fh Overlay Manager Interrupt (Microsoft LINK.EXE) ........ 5**30
Interrupt 40h Hard Disk BIOS ........................................ 5**31
Interrupt 41h Hard Disk Parameters .................................. 5**32
Interrupt 42h Pointer to screen BIOS entry .......................... 5**33
Interrupt 43h Pointer to EGA Graphics Character Table ............... 5**34
Interrupt 44h Pointer to graphics character table ................... 5**35
Interrupt 45h Reserved by IBM (not initialized) .................... 5**36
Interrupt 46h Pointer to second hard disk parameter block ........... 5**37
Interrupt 47h Reserved by IBM (not initialized) .................... 5**38
Interrupt 48h Cordless Keyboard Translation ......................... 5**39
Interrupt 49h Non-keyboard Scan Code Translation Table Address (PCjr) 5**40
Interrupt 4Ah Real-Time Clock Alarm (Convertible, PS/2) ............. 5**41
Interrupt 4Bh Reserved by IBM (not initialized) .................... 5**42
Interrupt 4Ch Reserved by IBM (not initialized) .................... 5**43
Interrupt 4Dh Reserved by IBM (not initialized) .................... 5**44
Interrupt 4Eh Reserved by IBM (not initialized) .................... 5**45
Interrupt 4Fh Reserved by IBM (not initialized) .................... 5**46
Interrupt 50-57 IRQ0-IRQ7 Relocation .................................. 5**47
Interrupt 58h Reserved by IBM (not initialized) .................... 5**48
Interrupt 59h Reserved by IBM (not initialized) .................... 5**49
Interrupt 5Ah Reserved by IBM (not initialized) ................... 5**50
Interrupt 5Bh Reserved by IBM (not initialized) .................... 5**51
Interrupt 5Ah Cluster Adapter BIOS entry address .................... 5**52
Interrupt 5Bh Reserved by IBM (not initialized) .................... 5**53
Interrupt 5Ch NETBIOS interface entry port, TOPS .................... 5**54
Interrupt 5Dh Reserved by IBM (not initialized) .................... 5**55
Interrupt 5Eh Reserved by IBM (not initialized) .................... 5**56
Interrupt 5Fh Reserved by IBM (not initialized) .................... 5**57
Interrupt 60h-67h User Program Interrupts ............................ 5**58
Interrupt 60h Network OS Interface .................................. 5**59
Interrupt 67h Expanded Memory Board Driver Interrupt ................ 5**60
Interrupt 68h Not Used (not initialized) ........................... 5**61
Interrupt 69h Not Used (not initialized) ........................... 5**62
Interrupt 6Ah Not Used (not initialized) ........................... 5**63
Interrupt 6Bh Not Used (not initialized) ........................... 5**64
Interrupt 6Ch System Resume Vector (Convertible) .................... 5**65
Interrupt 6Dh Not Used (not initialized) ........................... 5**66
Interrupt 6Eh Not Used (not initialized) ........................... 5**67
Interrupt 6Fh 10-Net API............................................. 5**68
Interrupt 70h IRQ 8, Real Time Clock Interrupt (AT, XT/286, PS/2) ... 5**69
Interrupt 71h IRQ 9, Redirected to IRQ 8 (AT, XT/286, PS/2) ......... 5**70
Interrupt 72h IRQ 10 (AT, XT/286, PS/2) Reserved .................. 5**71
Interrupt 73h IRQ 11 (AT, XT/286, PS/2) Reserved .................. 5**72
Interrupt 74h IRQ 12 Mouse Interrupt (PS/2) ........................ 5**73
Interrupt 75h IRQ 13, Coprocessor Error (AT) ........................ 5**74
Interrupt 76h IRQ 14, Hard Disk Controller (AT, XT/286, PS/2) ....... 5**75
Interrupt 77h IRQ 15 (AT, XT/286, PS/2) Reserved ................... 5**76
Interrupt 78h Not Used .............................................. 5**77
Interrupt 79h Not Used .............................................. 5**78
Interrupt 7Ah Reserved .............................................. 5**79
Interrupt 7Bh-7Eh Not Used by IBM .................................... 5**80
Interrupt 7Ch REXX-PC API ........................................... 5**81
Interrupt 7Fh IBM 8514/A Graphics Adapter API ....................... 5**82
Interrupt 80h-85h Reserved by BASIC .................................. 5**83
Interrupt 86h Int 18 when relocated by NETBIOS ...................... 5**84
Interrupt 86h-0F0h Used by BASIC when BASIC interpreter is running ... 5**85
Interrupt 0A4h Right Hand Man API .................................... 5**86
Interrupt 0D4h PC-MOS/386 API ........................................ 5**87
Interrupt 0E0h Digital Research CP/M-86 function calls ............... 5**88
Interrupt 0E1h PC Cluster Disk Server Information .................... 5**89
Interrupt 0E2h PC Cluster Program .................................... 5**90
Interrupt 0E4h Logitech Modula-2 v2.0 Monitor Entry ................ 5**91
Interrupt 0E5h Not Used .............................................. 5**92
Interrupt 0E6h Not Used .............................................. 5**93
Interrupt 0E7h Not Used .............................................. 5**94
Interrupt 0E8h Not Used .............................................. 5**95
Interrupt 0E9h Not Used .............................................. 5**96
Interrupt 0EAh Not Used .............................................. 5**97
Interrupt 0EBh Not Used .............................................. 5**98
Interrupt 0ECh Not Used .............................................. 5**99
Interrupt 0EDh Not Used ............................................. 5**100
Interrupt 0EEh Not Used ............................................. 5**101
Interrupt 0EFh GEM interface (Digital Research) ..................... 5**102
Interrupt 0F0h unknown .............................................. 5**103
Interrupts 0F1h-0FFh (absolute addresses 3C4h-3FFh) ................. 5**104
Interrupt 0F4h Not Used ............ ................................ 5**105
Interrupt 0F5h Not Used ............ ................................ 5**106
Interrupt 0F8h Set Shell Interrupt (OEM) ............................ 5**107
Interrupt 0F9h Reserved ............................................. 5**108
Interrupt 0FAh USART ready (RS-232C) ................................ 5**109
Interrupt 0FBh USART RS ready (keyboard) ............................ 5**110
Interrupt 0FCh Unknown ...............................................5**111
Interrupt 0FDh reserved for user interrupt .......................... 5**112
Interrupt 0FEh reserved by IBM ...................................... 5**113
Interrupt 0FFh reserved by IBM ...................................... 5**114
CHAPTER 6 DOS Control Blocks and Work Areas
DOS Address Space ..................................................... 6**1
Storage Blocks ........................................................ 6**2
Disk Transfer Area (DTA) .............................................. 6**3
Program Segment Prefix ................................................ 6**4
Memory Control Blocks ................................................. 6**5
DOS Program Segment ................................................... 6**6
CHAPTER 7 DOS File Information
File Management Functions ............................................. 7**1
FCB Function Calls .................................................... 7**2
Handle Function Calls ................................................. 7**3
Special File Handles .................................................. 7**4
Raw and Cooked File I/O ............................................... 7**5
Number of Open Files Allowed ......................................... 7**6
Restrictions on FCB Usage ............................................. 7**7
Restrictions on Handle usage .......................................... 7**8
Allocating Space to a File ............................................ 7**9
MSDOS / PCDOS Differences ............................................. 7**10
.COM File Structure ................................................... 7**11
.EXE File Structure ................................................... 7**12
The Relocation Table .................................................. 7**13
"NEW" .EXE Format (Microsoft Windows and OS/2) ........................ 7**14
Standard File Control Block ........................................... 7**15
Extended File Control Block ........................................... 7**16
Disk Transfer Area .................................................... 7**17
CHAPTER 8 DOS Disk Information
The DOS Area .......................................................... 8**1
The Boot Record ....................................................... 8**2
DOS File Allocation Table (FAT) ....................................... 8**3
Media Descriptor Byte ......................................... 8**4
12 Bit FATs ................................................... 8**5
16 Bit FATs ................................................... 8**6
32 Bit FATs ................................................... 8**7
DOS Disk Directory .................................................... 8**8
The Data Area ......................................................... 8**9
Floppy Disk Types ..................................................... 8**10
Hard Disk Layout ...................................................... 8**11
System Initialization ................................................. 8**12
Boot Record/Partition Table ........................................... 8**13
Hard Disk Technical Information ....................................... 8**14
Determining Hard Disk File Allocation ................................. 8**15
BIOS Disk Functions ................................................... 8**16
CHAPTER 9 Device Drivers
CHAPTER 10 Lotus/Intel/Microsoft Expanded Memory Specification
History ............................................................... 10**1
Uses of Expanded Memory ............................................... 10**2
DOS and Expanded Memory ............................................... 10**3
Different Memory Types ................................................ 10**4
AST/Quadram/Ashton-Tate Enhanced EMM .................................. 10**5
EMS Address Space Map ................................................. 10**6
Writing Programs That Use Expanded Memory ............................. 10**7
Page Frames ........................................................... 10**8
Calling the Manager ................................................... 10**9
Detecting EMS ......................................................... 10**10
Terminate and Stay Resident (TSR) Program Cooperation ................. 10**11
Expanded Memory Services Quick List ................................... 10**12
Expanded Memory Services .............................................. 10**13
LIM 3.2 Specification ......................................... 10**14
LIM 4.0 Specification ......................................... 10**15
AQA EEMS 3.2 Specification .................................... 10**16
VCPI API 1.0 .................................................. 10**17
Expanded Memory Manager Error Codes ................................... 10**18
Microsoft Extended Memory Specification 2.0 ........................... 10**19
CHAPTER 11 Conversion Between Operating Systems
Overview .............................................................. 11**1
Special Considerations ................................................ 11**2
Example Operating Systems ............................................. 11**3
Atari ST .............................................................. 11**4
CP/M .................................................................. 11**5
MacOS ................................................................. 11**6
AmigaDOS .............................................................. 11**7
OS/2 .................................................................. 11**8
UNIX .................................................................. 11**9
CHAPTER 12 Microsoft Windows API
Overview .............................................................. 12**1
Programming Windows ................................................... 12**2
Versions .............................................................. 12**3
Functions ............................................................. 12**4
Error Codes ........................................................... 12**5
CHAPTER 13 Network APIs
FTP Driver - PC/TCP Packet Driver Specification ....................... 13**1
10-Net Network ........................................................ 13**2
LANtastic LANOS API ................................................... 13**3
Novell NetWare 2.11 API ............................................... 13**4
APPC/PC ............................................................... 13**5
CHAPTER 14 Mouse Programming
General Information ................................................... 14**1
Register Usage ........................................................ 14**2
Interrupt 33h Function Requests ....................................... 14**3
Interrupt 10h Function Requests ....................................... 14**4
CHAPTER 15 Register-Level Programming
8555 Peripheral Interface ............................................. 15**1
8259 Interrupt Controller ............................................. 15**2
AT CMOS RAM Configuration ............................................. 15**3
CHAPTER 16 Video Programming
Quick List of BIOS Interrupt 10h Functions ............................ 16**1
BIOS Interrupt 10h Functions in Detail ................................ 16**2
CHAPTER 17 Multitasking Shells
Introduction .......................................................... 17**1
Programming Practices ................................................. 17**2
TopView/DESQview API (interrupt 15h, "System Services" interface) ..... 17**3
TopView/DESQview API (interrupt 16h, "BIOS Video" interface) .......... 17**4
CHAPTER 18 Viruses and Trojan Horses
CHAPTER 19 Tips and Tricks
MISCSTUF Miscellaneous Stuff
AFTERWRD Afterword
CREDITS Credits and Bibliography
A P P E N D I C E S
APPENDIX 1 Keyboard scan code chart
APPENDIX 2 ASCII character chart
APPENDIX 3 IBM PC character set
APPENDIX 4 IBM PC error code listing
APPENDIX 5 Addresses of various manufacturers
APPENDIX 6 Hard disk information
APPENDIX 7 Floppy and Tape Devices
APPENDIX 8 Pinouts of various connectors on the IBM PC
APPENDIX 9 Sizes of various drivers installed in CONFIG.SYS
APPENDIX 10 Common modem instruction sets
APPENDIX 11 Glossary of computer terminology
APPENDIX 12 Various busses used in MSDOS machines
APPENDIX 13 Common filename extensions
APPENDIX 14 Clock speeds of various expansion cards
APPENDIX 15 Header formats used by various archive utilities
APPENDIX 16 Miscellaneous Hardware Information
APPENDIX 17 HP LaserJet Setup Codes
APPENDIX 18 ANSI.SYS Escape Sequences
APPENDIX 19 DEC VT100 Escape Sequences
APPENDIX 20 Various Paint Program Formats
APPENDIX 21 Some Commonly Used Hot-Keys
APPENDIX 22 Sound Blaster API
APPENDIX 23 French-Canadian accented character chart
APPENDIX 24 Compuserve Graphic Image Format '89a
APPENDIX 25 Hex Chart
APPENDIX 26 Microsoft TSR Specification 1.0
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
C H A P T E R O N E
DOS AND THE IBM PC
C O N T E N T S
Some History .......................................................... 1**1
What is DOS? .......................................................... 1**2
Other Operating Systems ............................................... 1**3
Specific Versions of MS/PC-DOS ........................................ 1**4
The Operating System Heirarchy ........................................ 1**5
DOS Structure ......................................................... 1**6
DOS Initialization .................................................... 1**7
SOME HISTORY쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 1**1
Development of MSDOS/PCDOS began in October 1980, when IBM began searching
the market for an operating system for the yet-to-be-introduced IBM PC.
Microsoft had no 8086 real operating system to sell, but quickly made a deal
to license Seattle Computer Products' 86-DOS operating system, which had been
written by Tim Paterson earlier in 1980 for use on that company's line of 8086,
S100 bus micros. 86-DOS (also called QDOS, for Quick and Dirty Operating System)
had been written as more or less a 16-bit version of CP/M, since Digital
Research was showing no hurry in introducing CP/M-86.
This code was quickly polished up and presented to IBM for evaluation. IBM
had originally intended to use Digital Research's CP/M operating system, which
was the industry standard at the time.
Folklore reports various stories about the rift between DRI and IBM. The most
popular story claims Gary Kildall or DRI snubbed the IBM executives by flying
his airplane when the meeting was scheduled. Another story claims Kildall
didn't want to release the source for CP/M to IBM, which would be odd, since
they released it to other companies. One noted industry pundit claims
Kildall's wife killed the deal by insisting on various contract changes. I
suspect the deal was killed by the good ol'boy network. It's hard to imagine
a couple of junior IBM executives giving up when ordered to a task as simple
as licensing an operating system from a vendor. Wouldn't look good on their
performance reports. It would be interesting to hear IBM's story...
IBM found itself left with Microsoft's offering of "Microsoft Disk
Operating System 1.0". An agreement was reached between the two, and IBM agreed
to accept 86-DOS as the main operating system for thir new PC. Microsoft
purchased all rights to 86-DOS in July 1981, and "IBM Personal Computer DOS
1.0" was ready for the introduction of the IBM PC in October 1981. IBM
subjected the operating system to an extensive quality-assurance program,
reportedly found well over 300 bugs, and decided to rewrite the programs. This
is why PC-DOS is copyrighted by both IBM and Microsoft.
Some early OEM versions of DOS had different names, such as Compaq-DOS, Z-DOS,
Software Bus 86, etc. By version 2 Microsoft managed to persuade everyone but
IBM to refer to the product as "MS-DOS."
It is sometimes amusing to reflect on the fact that the IBM PC was not
originally intended to run MSDOS. The target operating system at the end of the
development was for a (not yet in existence) 8086 version of CP/M. On the other
hand, when DOS was originally written the IBM PC did not yet exist! Although
PC-DOS was bundled with the computer, Digital Research's CP/M-86 would probably
have been the main operating system for the PC except for two things - Digital
Research wanted $495 for CP/M-86 (considering PC-DOS was essentially free) and
many software developers found it easier to port existing CP/M software to DOS
than to the new version of CP/M.
The upgrade from DOS 3.3 to 4.0 was done in-house by IBM. DOS 4.0 was a
completely IBM product, later licensed back to Microsoft. In early 1990 IBM
announced that it was ceasing development of DOS and all further work would
be done solely by Microsoft.
Microsoft Press' "MSDOS Encyclopedia" shows a reproduction of a late
DOS 1.25 OEM brochure. Microsoft was touting future enhancements to
1.25 including Xenix-compatible pipes, process forks, and multitasking,
as well as "graphics and cursor positioning, kanji support, multi-user
and hard disk support, and networking." Microsoft certainly thought
big, but, alas, the forks, multitasking, and multiuser support never
came about, at least in US versions of DOS. Oddly, the flyer claims
that
"MS-DOS has no practical limit on disk size. MS-DOS uses 4-byte XENIX
OS compatible pointers for file and disk capacity up to 4 gigabytes."
Umm... yeah. One sort of gets the idea nobody at Microsoft had a hard
disk larger than 32 megabytes...
For the record they actually delivered:
Xenix-compatible pipes DOS 2.0 ("|" operator)
process forks, and multitasking eDOS 4.0 (not delivered in the US)
multi-user never delivered
graphics and cursor positioning DOS 2.0 (ANSI.SYS, more than likely)
kanji support DOS 2.01, 2.25 (double-byte char set)
hard disk support DOS 2.0 (subdirectories)
networking DOS 3.1 (file locking, MS Networks)
Early Microsoft ads pumped DOS' Xenix-like features and promised Xenix
functionality in future releases.
We'll probably never know what the real story was behind eDOS/DOS 4/
DOS 5/286DOS/OS2. Microsoft had announced their intent to build a
multitasking, multiuser version of MSDOS as early as 1982. They shipped
betas of "DOS 4.0" in '86 and early '87, before 3.3 was even announced.
Microsoft UK announced they had licensed 4.0 to Apricot Computer, and
the French Postal Service was supposed to be running it. I've never
been able to find out if Apricot ever shipped any 4.0 to end users.
Despite Gordon Letwin's acid comments about problems with the 80286
processor, I doubt the '286 was the barrier between users and a
multitasking MSDOS. I also doubt there was any shortage of programming
talent at Microsoft - Digital Research's Concurrent DOS and Software
Link's PC-MOS were developed without undue trouble.
MSDOS and PC-DOS have been run on more than just the IBM-PC and clones. Some
of the following have been done:
Hardware PC Emulation:
Apple II -> TransPC 8088 board
Apple MacIntosh -> AST 80286 board
Atari 400/800 -> Co-Power 88 board
Atari ST -> PC-Ditto II cartridge
Commodore Amiga 2000 -> 8088 or A2286D 80286 Bridge Board
IBM PC/RT -> 80286 AT adapter
Kaypro 2 -> Co-Power Plus board
Software PC Emulation:
Apple MacIntosh -> SoftPC
Atari ST -> PC-Ditto I
IBM RS/6000 -> DOS emulation
DOS Emulation:
AIX (IBM RS/6000) -> DOS emulation with "PCSIMulator"
OS/2 -> DOS emulation in "Compatibility Box"
QNX -> DOS window
SunOS -> DOS window
Xenix -> DOS emulation with DOSMerge
WHAT IS DOS?쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 1**2
DOS exists as a high-level interface between an application program and the
computer. DOS stands for "Disk Operating System", which reflects the fact that
its main original purpose was to provide an interface between the computer and
its disk drives.
DOS now lets your programs do simple memory management, I/O from the system
console, and assorted system tasks (time and date, etc) as well as managing
disk operations. Versions 3.1 and up also incorporate basic networking
functions.
With the introduction of installable device drivers and TSR (terminate but
stay resident) programs in DOS 2.0, the basic DOS functions may be expanded to
cover virtually any scale of operations required.
OTHER OPERATING SYSTEMS쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴 1**3
There are a number of compatible replacements for Microsoft's MSDOS. Some are:
Alloy 386 Multiware (multitasking control prog, licensed DOS)
Consortium Technologies MultiDOS (multitasking, multiuser)
Digital Research Concurrent DOS (multitasking)
Digital Research Concurrent DOS 386 (for 80386 computers)
Digital Research Concurrent DOS XM (multitasking, multiuser)
Digital Research DR-DOS 3.31 and 5.0 (PC-DOS clones)
Digital Research Multiuser DOS (multitasking, multiuser)
PC-MOS/386 (multitasking, multiuser)
Wendin-DOS (multitasking, multiuser)
VM/386 (multitasking)
Various other operating systems are available for the IBM PC. These include:
Digital Research CP/M-86
Digital Research Concurrent CP/M-86 (multitasking)
Minix (multitasking UNIX workalike)
Pick (database-operating system)
QNX (multitasking, multiuser)
UNIX (various systems from IBM itself, Microsoft-SCO, Bell, and various UNIX
clones, single and multi user) (AIX, Xenix, AT&T System V, etc.)
"Shell" programs exist which use DOS only for disk management while they more
or less comprise a new operating system. These include:
DesQview Windows OmniView
GEM TopView TaskView
GeoWorks
Systems using the NEC V-series CPUs can execute Intel 8080/8085 8-bit
instructions as well as the 16-bit 8088-up instructions. They can run standard
Digital Research 8-bit CP/M and MP/M directly, as well as other operating
systems developed for that processor.
SPECIFIC VERSIONS OF MS/PC-DOS쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 1**4
DOS 1.x is essentially 86-DOS. DOS 2.x kept the multiple file layout (the two
hidden files and COMMAND.COM) but for all practical purposes is an entirely
different operating system with backwards compatibility with 1.x. I seriously
doubt there has been much code from 1.x retained in 2.x. DOS 3.x is merely an
enhancement of 2.x; there seems little justification for jumping a whole
version number. The disk handling routines were considerably extended in 3.1,
allowing disk access in a "virtual" fashion, independent of whether the drive
was a local or network device. DOS 4.0, originating as it did from outside
Microsoft, can justify a version jump. Unfortunately, 4.0 seemed to have very
little reason to justify its existence - virtually all of its core features
could be found in one version or another of DOS 3.x. According to Microsoft's
Gordon Letwin, DOS 5.0 was a complete rewrite with the kernel done in hand
optimized assembly language.
DOS version nomenclature: major.minor.minor. The digit to the left of the
decimal point indicates a major DOS version change. 1.0 was the first version.
2.0 added support for subdirectories, 3.0 added support for networking, 4.0
added some minimal support for Lotus-Intel-Microsoft EMS.
The first minor version indicates customization for a major application. For
example, 2.1 for the PCjr, 3.3 for the PS/2s. The second minor version does not
seem to have any particular meaning.
The main versions of DOS are:
86-DOS February 1981 Paterson's Quick'n'Dirty DOS first runs on PC
PC-DOS 1.0 August 1981 original IBM release
PC-DOS 1.05 -------- ---- fixes to BASIC interpreter
PC-DOS 1.1 June 1982 bugfix, double sided drive support
MS-DOS 1.25 July 1982 for early compatibles. This is the first non-IBM
OEM version
PC-DOS 2.0 March 1983 for PC/XT, Unix-type subdirectory support,
installable device drivers, I/O redirection,
subdirectories, hard disk support, handle calls
PC-DOS 1.85 April 1983 internal IBM - extended 1.1 - not released
MS-DOS 2.01 -------- 1983 first support for individual country formats, Kanji
PC-DOS 2.1 October 1983 for IBM PCjr, bugfixes for 2.0. No country support
MS-DOS 2.11 October 1983 basically a cross of PC-DOS 2.1 and MS-DOS 2.01
MS-DOS 2.12 -------- ---- special version for TI Professional
PC-DOS 3.0 August 1984 1.2 meg drive for PC/AT, some new system calls,
new external programs, 16-bit FAT, specific support
for IBM network
MS-DOS 3.05 -------- 1984 first OEM version of 3.x
PC-DOS 3.1 November 1984 bugfix for 3.0, implemented generic network support
MS-DOS 2.25 October 1985 extended foreign language support
PC-DOS 3.2 January 1986 720k 3.5 inch drive support, special support for
laptops (IBM PC Convertible), XCOPY
MS-DOS 4.0 April 1986 multitasking (Europe only) - withdrawn from market
PC-DOS 3.3 April 1987 for PS/2 series, 1.44 meg support, multiple DOS
partition support, code page switching, improved
foreign language support, some new function calls,
support for the AT's CMOS clock.
MS-DOS 3.31 November 1987 over-32 meg DOS partitions. Different versions
from different OEMs (not Microsoft). Compaq and
Wyse are most common.
PC-DOS 3.4 -------- ---- internal IBM - not released (4.0 development)
MS-DOS 2.11R -------- 1988 bootable ROM DOS for Tandy machines
PC-DOS 4.0 August 1988 32mb limit officially broken, minor EMS support,
more new function calls, enhanced network support
for external commands
MS-DOS 4.01 January? 1989 Microsoft version with some bugfixes
MS-DOS 3.21R September1989 DOS in ROM, Flash File System for laptops
MS-DOS 3.3R -------- 1990 DOS in ROM, introduced for TI laptops
MS-DOS 5.0 June 1991 new high memory support, uses up to 8 hard disks,
command line editor and aliasing, 2.88 floppies
IBM's PC-DOS was long considered to be the "standard" version of DOS. Now
that MS 5.0 is a commercial product most developers will probably write to it.
Microsoft's policy has been to sell DOS only to OEMs. Despite this, they
sold small quantities of DOS 3.2, 3.3, and 4.0 without insurmountable
difficulties. DOS 5.0 was conceived from the beginning as an over-the-counter
retail product.
Incidentally, IBM refers to its DOS as "The IBM Personal Computer DOS." The
term "PCDOS" is a trademark of IBM's rival DEC.
Some versions of MS-DOS varied from PC-DOS in the available external commands.
Some OEMs only licensed the basic operating system code (the xxxDOS and xxxBIO
programs, and COMMAND.COM) from Microsoft, and either wrote the rest themselves
or contracted them from outside software houses like Phoenix. Most of the
external programs for DOS 3.x and 4.x are written in "C" while the 1.x and 2.x
utilities were written in assembly language. Other OEMs required customized
versions of DOS for their specific hardware configurations, such as Sanyo 55x
and early Tandy computers, which were unable to exchange their DOS with the IBM
version.
PC-DOS 3.0 was extremely buggy on release. It did not handle the DOS
environment correctly and there were numerous documented problems with the
batch file parser. The network support code was also nonfunctional in that DOS
version. It is recommended that users upgrade to at least version 3.1.
DEC MSDOS versions 2.11 for the Rainbow had the ANSI.SYS device driver built
into the main code. The Rainbow also used a unique quad density, single-sided
floppy drive and its DOS had special support for it.
IBM had a version 1.85 of PC-DOS in April 1983, after the introduction of DOS
2.0. It was evidently for internal use only, supported multiple drive file
searches (a primitive form of PATH), builtin MODE sommands for screen support,
a /P parameter for TYPE for paused screens, an editable command stack like the
public domain DOSEDIT.COM utility, and could be set up to remain completely
resident in RAM instead of a resident/transient part like normal DOS. It is a
pity some of the neat enhancements didn't make it into DOS 2.0. IBM also had
an "internal use only" version 3.4, evidently used while developing DOS 4.0.
Digital Research's DR-DOS is the first widely available DOS clone. Version
3.4, released in June 1988, was the one first available to the American public.
It was somewhat buggy and its use is not recommended. DR 3.41 is extremely
compatible and its use should pose no problems on any machine. DR-DOS 5.0
(released May, 1990) is functionally equivalent to MS-DOS 5.0. For all
practical purposes, MS 5.0 is a clone of DR 5.0, since DR beat MS to market by
over a year. According to Greg Ewald, DRI's DR-DOS product manager, DR-DOS was
developed from Concurrent DOS 386 with the multiuser and multitasking code
stripped out.
Some versions of DOS used in compatibles do not maintain the 1.x, 2.x, ...
numbering system. Columbia Data Products computers labeled DOS 1.25 as DOS
2.0. Early Compaqs labeled DOS 2.0 as DOS 1.x. Other versions incorporated
special features - Compaq DOS 3.31 and Wyse DOS 3.21 both support >32mb disk
partitions in the same fashion as DOS 4.x.
AT&T DOS 3.1 differs from generic MSDOS 3.10 in its use of cluster-size and
file allocation table structures. AT&T DOS appears to use rules not from
version 3, but rather those from version 2.
Epson Equity III and ComputerLand 3.10 DOS's appear to use cluster techniques
that are a cross between versions 2 and 3. On type DOS partitions, these DOS's
use 3.x rules if the partition is larger than 32,680 sectors in total size.
This implies 16 bit FAT entries as well. On partitions below this size, they
will use 2.x rules, including the 12 bit FAT entries.
Zenith DOS 3.x and Wyse DOS 3.2 have a builtin internal device driver to
handle up to 4 32Mb DOS partitions on a single hard disk. Wyse DOS 3.31 will
handle single partitions up to 512Mb with a 32-bit FAT.
According to PC Week Magazine, July 4, 1988, Arabic versions of MSDOS are
shipping with a hardware copy-protection system from Rainbow Technologies.
This is similar to the short-lived system used by AutoCAD 2.52 and a very few
other MSDOS programs, where an adapter block is plugged into the parallel port
and software makes use of coded bytes within the block. This type of copy
protection has been common on Commodore products for several years, where it is
called a "dongle."
The AutoCAD dongle was defeated by a small program written within weeks of
version 2.52's debut. Version 2.62 was released 3 months later, without the
dongle. The DOS dongle will, however, prevent the system from booting at all
unless it is found.
This makes the Arabic version of MSDOS the first copy-protected operating
system, a dubious distinction at best. The modifications to the operating
system to support the dongle are not known at this time. Frankly, it would
seem that burning the operating system into ROMs would be cheaper and simpler.
Versions of DOS sold in Great Britain are either newer than those sold in the
US or use a different numbering system. DOS 3.4, 4.0, 4.1, 4.2, and 4.3 had
been released there between the US releases of 3.3 and 4.0.
MSDOS 4.0 (eDOS) was introduced in mid-1987 in Europe (at SICOB in Paris and
sometime earlier by Apricot Computer in the UK). It offered multitasking
provided applications were specially written for it.
David Fraser (Microsoft UK Managing Director) is on record saying that "DOS
4.0 is unlikely to set the world alight and is of interest only to specific
OEMs who want its features for networking and communications." Standard DOS
applications will run under DOS 4.x as a foreground task according to uncertain
information. It differs from earlier versions only in allowing background tasks
to run. For further information, see Chapter 4.
Microsoft changed their OEM licensing agreements between DOS versions 2.x and
3.x. OEM versions of DOS 3.x must maintain certain data areas and undocumented
functions in order to provide compatibility with the networking features of the
operating system. For this reason, TSR programs will be much more reliable
when operating under DOS 3.x.
Several versions of DOS have been modified to be run out of ROM. The Sharp
PC5000 had MSDOS 1.25 in ROM, and the Toshiba 1000 and some Tandy 1000 models
have MSDOS 2.11 in ROM. In mid September 1989 Microsoft introduced 3.21R ROMs
for laptops, and in early '90 Texas Instruments laptops were the first to get
the 3.3R ROMs. Digital Research has also announced its DR-DOS 3.41 and 5.0 is
available in a ROM version and Award Software is marketing DOS cards to OEMs
as a plug-in to ISA-bus machines.
IBM's release of DOS 4.0 (and the immediate subsequent release of a bugfix)
was a dubious step "forward." DOS 4.0 was the first version of DOS to come with
a warranty; the catch is that IBM warranted it only for a very slim list of
IBM-packaged software. 4.0 had some minor EMS support, support for large hard
disks, and not much else. With its voracious RAM requirements and lack of
compatibility with previous versions of DOS (many major software packages
crashed under DOS 4.0), plus the increase in price to a cool $150, there was
no great rush to go to that version of DOS.
Microsoft undertook development of MSDOS 5.0 in early 1990, soliciting
input from Usenet, BIX, and Compuserve among others. 5.0 is a functional
clone of Digital Research's DR-DOS 5.0. 5.0's compatibility was assured
by what has been claimed as the largest beta-test program in history -
in his address to the Boston Computer Society, Bill Gates announced over
7,500 testers were involved.
THE OPERATING SYSTEM HIERARCHY쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 1**5
The Disk Operating System (DOS) and the ROM BIOS serve as an insulating layer
between the application program and the machine, and as a source of services
to the application program.
As the term 'system' might imply, DOS is not one program but a collection
of programs designed to work together to allow the user access to programs
and data. Thus, DOS consists of several layers of "control"programs and a set
of "utility" programs.
The system hierarchy may be thought of as a tree, with the lowest level being
the actual hardware. The 8088 or V20 processor sees the computer's address
space as a ladder one byte wide and one million bytes long. Parts of this
ladder are in ROM, parts in RAM, and parts are not assigned. There are also
65,536 "ports" that the processor can use to control devices.
The hardware is normally addressed by the ROM BIOS, which will always know
where everything is in its particular system. The chips may usually also be
written to directly, by telling the processor to write to a specific address or
port. This sometimes does not work as the chips may not always be at the same
addresses or have the same functions from machine to machine.
DOS STRUCTURE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴 1**6
DOS consists of four components:
* The boot record
* The ROM BIOS interface (IBMBIO.COM, DRBIOS.SYS, or IO.SYS)
* The DOS program file (IBMDOS.COM, DRBDOS.SYS, or MSDOS.SYS)
* The command processor (COMMAND.COM or aftermarket replacement)
* The Boot Record
The boot record begins on track 0, sector 1, side 0 of every diskette prepared
by the DOS FORMAT command. The boot record is placed on diskettes to produce an
error message if you try to start up the system with a nonsystem diskette in
drive A. For hard disks, the boot record resides on the first sector of the DOS
partition. All media supported by DOS use one sector for the boot record.
* Read Only Memory (ROM) BIOS Interface and Extensions
The file IBMBIO.COM or IO.SYS is the interface module to the ROM BIOS.
This file provides a low-level interface to the ROM BIOS device routines and
may contain extensions or changes to the system board ROMs. Some compatibles do
not have a ROM BIOS to extend, and load the entire BIOS from disk. (Sanyo 55x,
Viasyn machines). Some versions of MSDOS, such as those from Compaq's MS-DOS
and Digital Research's DRDOS 5.0, are named IBMBIO.COM but are not IBM files.
These low-level interface routines include the instructions for performing
operations such as displaying information on the screen, reading the keyboard,
sending data out to the printer, operating the disk drives, and so on. It is
the operating system's means of controlling the hardware. IBMBIO.COM contains
any modifications or updates to the ROM BIOS that are needed to correct any
bugs or add support for other types of hardware such as new disk drives. By
using IBMBIO.COM to update the ROM BIOS on the fly when the user turns on their
computer, IBM does not need to replace the ROM BIOS chip itself, but makes any
corrections through the cheaper and easier method of modifying the IBMBIO.COM
file instead.
IBMBIO.COM also keeps track of hardware operations on an internal stack or
"scratch pad" area for the operating system to save information such as
addresses it will need, etc. An example of the use for this stack can be seen
when running a program such as a word processor. If you have told the word
processor to save your letter, it will write the data to your disk. During this
time, if you start typing some more information, the keyboard generates a
hardware interrupt. Since you don't want the process of writing the information
to the disk to be interrupted, DOS allocates a slot in the stack for the
keyboard's hardware interrupt and when it gets a chance, (probably after the
data has been written to the disk), it can process that interrupt and pick up
the characters you may have been typing. The STACKS= command in DOS 3.2+'s
CONFIG.SYS file controls the number of stack frames available for this
purpose.
IBMBIO.COM also reads your CONFIG.SYS file and installs any device drivers
(i.e. DEVICE=ANSI.SYS) or configuration commands it may find there.
* The DOS Program
The actual DOS program is the file IBMDOS.COM or MSDOS.SYS. It provides a high-
level interface for user (application) programs. This program consists of file
management routines, data blocking/deblocking for the disk routines, and a
variety of built-in functions easily accessible by user programs.
When a user program calls these function routines, they accept high-level
information by way of register and control block contents. When a user program
calls DOS to perform an operation, these functions translate the requirement
into one or more calls to IBMBIO.COM, MSDOS.SYS or system hardware to complete
the request.
This section is often referred to as the "kernel" by systems programmers.
* The Command Interpreter
The command interpreter, COMMAND.COM, is the part you interact with on the
command line. COMMAND.COM has three parts. IBM calls them the "resident
portion", the "initialization portion" and the "transient portion".
IBM's original documentation spoke of installing alternate command
interpreters (programs other than COMMAND.COM) with the SHELL= statement in
CONFIG.SYS. Unfortunately, IBM chose not to document much of the interaction
between IBMDOS.COM and IBMBIO.COM. By the time much of the interaction was
widely understood, many commercial software programs had been written to use
peculiarities of COMMAND.COM itself.
Several programs exist that perform as actual "shells" by completely replacing
COMMAND.COM and substituting their own command interpreter to use with the
hidden DOS files. Examples are Command Plus, a commercial package, and the
shareware 4DOS and FlexShell packages. Both supply greatly enhanced batch
language and editing capabilities.
NOTE: DOS 3.3+ checks for the presence of a hard disk, and will default to
COMSPEC=C:\. Previous versions default to COMSPEC=A:\. Under some DOS
versions, if COMMAND.COM is not immediately available for reloading
(i.e., swapping to a floppy with COMMAND.COM on it) DOS may crash.
Resident Portion:
The resident portion resides in memory immediately following IBMDOS.COM and its
data area. This portion contains routines to process interrupts 22h (Terminate
Address), 23h (Ctrl-Break Handler), and 24h (Critical Error Handler), as well as
a routine to reload the transient portion if needed. For DOS 3.x, this portion
also contains a routine to load and execute external commands, such as files
with exensions of COM or EXE.
When a program terminates, a checksum is used to determine if the application
program overlaid the transient portion of COMMAND.COM. If so, the resident
portion will reload the transient portion from the area designated by COMSPEC=
in the DOS environment. If COMMAND.COM cannot be found, the system will halt.
All standard DOS error handling is done within the resident portion of
COMMAND.COM. This includes displaying error messages and interpreting the
replies to the "Abort, Retry, Ignore, Fail?" message.
Since the transient portion of COMMAND.COM is so large (containing the
internal commands and all those error messages), and it is not needed when the
user is running an application it can be overlaid that program if that
application needs the room. When the application is through, the resident
portion of COMMAND.COM brings the transient portion back into memory to show
the prompt. This is why you will sometimes see the message "Insert disk with
COMMAND.COM". It needs to get the transient portion off the disk since it was
overlaid with the application program.
The initialization portion of COMMAND.COM follows the resident portion and is
given control during the bootup procedure. This section actually processes the
AUTOEXEC.BAT file. It also decides where to load the user's programs when they
are executed. Since this code is only needed during startup, it is overlaid by
the first program which COMMAND.COM loads.
The transient portion is loaded at the high end of memory and it is the
command processor itself. It interprets whatever the user types in at the
keyboard, hence messages such as "Bad command or file name" for when the user
misspells a command. This portion contains all the internal commands (i.e.
COPY, DIR, RENAME, ERASE), the batch file processor (to run .BAT files) and
a routine to load and execute external commands which are either .COM or
.EXE files.
The transient portion of COMMAND.COM produces the system prompt, (C>), and
reads what the user types in from the keyboard and tries to do something with
it. For any .COM or .EXE files, it builds a command line and issues an EXEC
function call to load the program and transfer control to it.
DOS INITIALIZATION쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 1**7
The system is initialized by a software reset (Ctrl-Alt-Del), a hardware reset
(reset button), or by turning the computer on. The Intel 80x8x series processors
always look for their first instruction at the end of their address space
(0FFFF0h) when powered up or reset. This address contains a jump to the first
instruction for the ROM BIOS.
Built-in ROM programs (Power-On Self-Test, or POST, in the IBM) check machine
status and run inspection programs of various sorts. Some machines set up a
reserved RAM area with bytes indicating installed equipment (AT and PCjr).
When the ROM BIOS finds a ROM on an adapter card, it lets that ROM take
control of the system so that it may perform any set up necessary to use the
hardware or software controlled by that ROM. The ROM BIOS searches absolute
addresses C8000h through E0000h in 2K increments in search of a valid ROM.
A valid ROM is determined by the first few bytes in the ROM. The ROM will have
the bytes 55h, AAh, a length indicator and then the assembly language
instruction to CALL FAR (to bring in a "FAR" routine). A checksum is done on
the ROM to verify its integrity, then the BIOS performs the CALL FAR to bring
in the executible code. The adapter's ROM then performs its initialization
tasks and hopefully returns control of the computer back to the ROM BIOS so it
can continue with the booting process.
The ROM BIOS routines then look for a disk drive at A: or an option ROM
(usually a hard disk) at absolute address C:800h. If no floppy drive or option
ROM is found, the BIOS calls int 19h (ROM BASIC if it is an IBM) or displays
an error message.
If a bootable disk is found, the ROM BIOS loads the first sector of information
from the disk and then jumps into the RAM location holding that code. This code
normally is a routine to load the rest of the code off the disk, or to "boot"
the system.
The following actions occur after a system initialization:
1. The boot record is read into memory and given control.
2. The boot record then checks the root directory to assure that the first
two files are IBMBIO.COM and IBMDOS.COM or their OEM equivalents. These
must be the first two files, and they must be in that order (IBMBIO.COM
first, with its sectors in contiguous order).
NOTE: IBMDOS.COM need not be contiguous in version 3.x+.
3. The boot record loads IBMBIO.COM into memory.
4. The initialization code in IBMBIO.COM loads IBMDOS.COM, determines
equipment status, resets the disk system, initializes the attached
devices, sets the system parameters and loads any installable device
drivers according to the CONFIG.SYS file in the root directory (if
present), sets the low-numbered interrupt vectors, relocates IBMDOS.COM
downward, and calls the first byte of DOS.
NOTE: CONFIG.SYS may be a hidden file.
5. DOS initializes its internal working tables, initializes the interrupt
vectors for interrupts 20h through 27h, and builds a Program Segment
Prefix for COMMAND.COM at the lowest available segment. For DOS versions
3.10 up, DOS also initializes the vectors for interrupts 0Fh through 3Fh.
An initialization routine is included in the resident portion and assumes
control during startup. This routine contains the AUTOEXEC.BAT file
handler and determines the segment address where user application programs
may be loaded. The initialization routine is then no longer needed and is
overlaid by the first program COMMAND.COM loads.
NOTE: AUTOEXEC.BAT may be a hidden file.
6. IBMDOS.COM uses the EXEC function call to load and start the top-level
command processor. The default command processor is COMMAND.COM in the
root directory of the boot drive. If COMMAND.COM is in a subdirectory
or another command processor is to be used, it must be specified by a
SHELL= statement in the CONFIG.SYS file.
A transient portion is loaded at the high end of memory. This is the
command processor itself, containing all of the internal command
processors and the batch file processor. For DOS 2.x, this portion also
contains a routine to load and execute external commands, such as files
with extensions of COM or EXE.
This portion of COMMAND.COM also produces the DOS prompt (such as "A>"),
reads the command from the standard input device (usually the keyboard or
a batch file), and executes the command. For external commands, it builds
a command line and issues an EXEC function call to load and transfer
control to the program.
note 1) COMMAND.COM may be a hidden file.
2) For IBM DOS 2.x, the transient portion of the command processor
contains the EXEC routine that loads and executes external commands.
For MSDOS 2.x+ and IBM DOS 3.x+, the resident portion of the command
processor contains the EXEC routine.
3) IBMDOS only checks for a file named "COMMAND.COM". It will load
any file of that name if no SHELL= command is used.
That pretty much covers the bootup process. After the command processor is
loaded, it runs the AUTOEXEC.BAT file and then the user gets their prompt to
begin working.
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
C H A P T E R T W O
CPU Port Assignments, System Memory Map, BIOS Data Area, Interrupts 00h to 09h
C O N T E N T S
Introduction .......................................................... 2**1
System Memory Map ..................................................... 2**2
A Brief Guide to Current Memory Terminology ........................... 2**3
PC Port Assignment .................................................... 2**4
Reserved Memory Locations ............................................. 2**5
Absolute Addresses .................................................... 2**6
The IBM PC System Interrupts (Overview) ............................... 2**7
Quick Chart of Interrupts 00h-0FFh .................................... 2**8
The IBM-PC System Interrupts 00h-0Fh (in detail) ...................... 2**9
Introduction .......................................................... 2**1
For consistency in this reference, all locations and offsets are in
hexadecimal unless otherwise specified. All hex numbers are prefaced with a
leading zero if they begin with an alphabetic character, and are terminated
with a lowercase H (h). The formats vary according to common usage.
System Memory Map ..................................................... 2**2
The IBM PC handles its address space in 64k segments, divided into 16k
fractions and then further as necessary.
旼컴컴컫컴컴컫컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
퀂tart 퀂tart쿮nd � �
쿪ddr. 쿪ddr.쿪ddr.� usage �
�(dec) � (hex) � �
쳐컴컴컨컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� *640k RAM Area* �
쳐컴컴컫컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0k � � start of RAM, first K is interrupt vector table �
� 16k �00000-03FFF� PC-0 system board RAM ends �
� 32k �04000-07FFF� �
� 48k �08000-0BFFF� �
쳐컴컴컵컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 64k �10000-13FFF� PC-1 system board RAM ends �
� 80k �14000-17FFF� �
� 96k �18000-1BFFF� �
� 112k �1C000-1FFFF� �
쳐컴컴컵컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 128k �20000-23FFF� �
� 144k �24000-27FFF� �
� 160k �28000-2BFFF� �
� 176k �2C000-2FFFF� �
쳐컴컴컵컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 192k �30000-33FFF� �
� 208k �34000-37FFF� �
� 224k �38000-3BFFF� �
� 240k �3C000-3FFFF� �
쳐컴컴컵컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 256k �40000-43FFF� PC-2 system board RAM ends �
� 272k �44000-47FFF� �
� 288k �48000-4BFFF� �
� 304k �4C000-4FFFF� �
쳐컴컴컵컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 320k �50000-53FFF� �
� 336k �54000-57FFF� �
� 352k �58000-5BFFF� �
� 368k �5C000-5FFFF� �
쳐컴컴컵컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 384k �60000-63FFF� �
� 400k �64000-67FFF� �
� 416k �68000-6BFFF� �
� 432k �6C000-6FFFF� �
쳐컴컴컵컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 448k �70000-73FFF� �
� 464k �74000-77FFF� �
� 480k �78000-7BFFF� �
� 496k �7C000-7FFFF� �
쳐컴컴컵컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 512k �80000-83FFF� �
� 528k �84000-87FFF� �
� 544k �88000-8BFFF� the original IBM PC-1 BIOS limited memory to 544k �
� 560k �8C000-8FFFF� �
쳐컴컴컵컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 576k �90000-93FFF� �
� 592k �94000-97FFF� �
� 609k �98000-9BFFF� �
� 624k �9C000-9FFFF� to 640k (top of RAM address space) �
쳐컴컴컨컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿌0000 ***** 64k ***** EGA/VGA starting address �
쿌0000 ***** 64k ***** Toshiba 1000 DOS ROM (MS-DOS 2.11V) �
쳐컴컴컫컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 640k 쿌0000-A95B0� MCGA 320x200 256 color video buffer �
� � -AF8C0� MCGA 640x480 2 color video buffer �
� � -A3FFF� �
� 656k 쿌4000-A7FFF� �
� 672k 쿌8000-ABFFF� this 64k segment may be used for contiguous DOS �
� 688k 쿌C000-AFFFF� RAM with appropriate hardware and software �
쳐컴컴컨컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿍0000 ***** 64k ***** mono and CGA address �
쳐컴컴컫컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 704k 쿍0000-B3FFF� 4k monochrome display | The PCjr and early Tandy 1000�
� 720k 쿍4000-B7FFF� | BIOS revector direct write to�
� 736k 쿍8000-BBFFF� 16k CGA uses | the B8 area to the Video Gate�
� 756k 쿍C000-BFFFF� | Array and reserved system RAM�
쳐컴컴컨컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿎0000 ***** 64k *************** expansion ROM �
쳐컴컴컫컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 768k 쿎0000-C3FFF� 16k EGA BIOS C000:001E EGA BIOS signature (letters IBM �
� 784k 쿎4000-C5FFF� �
� 쿎6000-C63FF� 256 bytes Professional Graphics Display comm. area �
� 쿎6400-C7FFF� �
� 800k 쿎8000-CBFFF� 16k hard disk controller BIOS, drive 0 default �
� 쿎A000 � some 2nd floppy (high density) controller BIOS �
� 816k 쿎C000-CDFFF� 8k IBM PC Network NETBIOS �
� 쿎E000-CFFFF� �
쳐컴컴컨컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿏0000 ***** 64k ***** expansion ROM �
쳐컴컴컫컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 832k 쿏0000-D7FFF� 32k IBM Cluster Adapter | PCjr first ROM cartridge �
� � DA000� voice communications | address area. �
� 848k 쿏4000-D7FFF� | Common expanded memory board �
� 864k 쿏8000-DBFFF� | paging area. �
� 880k 쿏C000-DFFFF� | �
� 쿏E000 � TI Pro default video buffer, 4k in length �
쳐컴컴컨컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿐0000 ***** 64k ***** expansion ROM �
쳐컴컴컫컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 896k 쿐0000-E3FFF� | PCjr second ROM cartridge �
� 912k 쿐4000-E7FFF� | address area �
� 928k 쿐8000-EBFFF� | �
� 944k 쿐C000-EFFFF� | spare ROM sockets on AT �
쳐컴컴컨컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿑0000 ***** 64k ***** system �
쳐컴컴컫컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 960k 쿑0000-F3FFF� reserved by IBM | cartridge address �
� 976k 쿑4000- � | area (PCjr cartridge �
� 쿑6000 � ROM BASIC Begins | BASIC) �
� 992k 쿑8000-FB000� | �
� 1008k쿑C000-FFFFF� ROM BASIC and original | �
� � � BIOS (Compatibility BIOS | �
� � � in PS/2) | �
� 1024k� FFFFF� end of memory (1024k) for 8088 machines �
쳐컴컴컵컴컴컴컴컴컨컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 384k �100000-15FFFF� 80286/AT extended memory area, 1Mb motherboard �
� 15Mb �100000-FFFFFF� 80286/AT extended memory address space �
� 15Mb �160000-FDFFFF� Micro Channel RAM expansion (15Mb extended memory) �
� 128k 쿑E0000-FFFFFF� system board ROM (PS/2 Advanced BIOS) �
쳐컴컴컵컴컴컴컴컴컴컨컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 64k 쿎0000000-C000FFFF� Weitek "Abacus" math coprocessor memory-mapped I/O �
읕컴컴컨컴컴컴컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
Note that the ROM BIOS has a duplicated address space which causes it to
"appear" both at the end of the 1 megabyte real mode space and at the end of
the 16 megabyte protected mode space. The addresses from 0E0000 to 0FFFFF are
equal to 0FE0000 to 0FFFFFF. This is necessary due to differences in the memory
addressing between Real and Protected Modes.
A Brief Guide to Current Memory Terminology ........................... 2**3
LOW MEMORY - 0000h to around 0:5(something), comprising the 80x8x interrupt
vector table, the BIOS Data Area, DOS Data Area, etc.
CONVENTIONAL MEMORY - from the end of low memory to the beginning of the
"reserved by IBM" A000 segment (640k).
HIGH MEMORY - originally noncontiguous RAM stuffed into the "reserved for
ROM expansion" areas, typically segments D000 and E000. DOS
normally can't access this memory without a driver of some
sort, but it's easy to put RAMdisks and stuff in there.
CONVENTIONAL MEMORY - extra RAM stuck at A000, assuming the machine already
has 640k, appears as conventional memory accessible to DOS
and applications. IBM clones can typically add 64k before
bumping into a mono card or 96k before hitting a color card.
This address is part of the EGA/VGA video RAM area and most
EGA cards don't like system memory at A000.
EXPANDED MEMORY - LIM 3.2, LIM 4.0, or EEMS 3.2 bank switched memory. A
RAM "window" allows an app to save a block of RAM to an expansion
board. The window size and location varies according to the
EMS standard being used.
EXTENDED MEMORY - this is the "native mode" address space of the 80286 and
later chips. The "real mode", or 8088 addressing scheme,
sees RAM as a collection of segments and offsets with a limit
on segment size. "Protected mode" addressing uses a flat linear
addressing scheme. 8088 and 80188 chips do not have extended
memory.
HIGH MEMORY - by fiddling a bit with the segment/offset stuff, you can
get an extra block of addressable 8088-mode memory just over
the 1 meg address space. Microsoft issued their "HMA" (High
Memory Area) standard to try to standardize use of this block.
Though it really is "high" memory, "high" had for many years
referred to memory between 640k and 1mb. This creates more
confusion for new programmers.
EMS - this is expanded memory as described above
XMS - Microsoft is pushing an "Extended Memory Standard" which defines
a page-switching scheme much like EMS. The only real difference is
that XMS uses protected-mode RAM instead of a special paged RAM board.
XMS - some severely brain-damaged jerk at IBM issued documentation for some
IBM *EMS* boards referring to the boards as *XMS*. This was a classic
blunder, and now some IBM-followers are picking up the aberrant
terminology. This is guaranteed to confuse some people. To make it
simple, if it needs an expansion board, it is EMS no matter what the
vendor calls it.
PC Port Assignment .................................................... 2**4
These are functions common across the IBM range. The PCjr, PC-AT, PC
Convertible and PS/2 (both buses) have enhancements. In some cases, the
AT and PS/2 series ignore, duplicate, or reassign ports arbitrarily. If
your code incorporates specific port addresses for video or system board
control it would be wise to have your application determine the machine
type and video adapter and address the ports as required.
hex address Function Models
PCjr|PC|XT|AT|CVT|M30|PS2
0000-000F 8237 DMA controller PC
0010-001F 8237 DMA controller AT PS2
0020-0027 8259A interrupt controller
0020-002F IOSGA interrupt function PS2
0020-003F 8259A interrupt controller (AT)
0020-0021 interrupt controller 1, 8259A PC AT PS2
0040-0043 programmable timer 8253 PC
0040-0047 programmable timers PS2
0040-005F 8253-5 programmable timers AT
note 1) 0041 was memory refresh in PCs. Not used in PS/2.
2) A few early 80386 machines used static RAM and did
not use refresh at all. The PCjr refreshes by the
video vertical retrace signal.
0060-0063 keyboard controller 8255A PC
0060-006F 8042 keyboard controller AT
0060 IOSGA keyboard input port PS2
0061 speaker PCjr PC XT AT CVT
0061 IOSGA speaker control M30 PS2
0061 On some clones, setting or clearing bit 2 controls Turbo mode
0061 Toshiba 1000 - system command
0062 IOSGA configuration control M30 PS2
0062 Toshiba 1000 - System Status, port C
0063 SSGA, undocumented PS2
0063 Toshiba 1000 - mode set
0064 keyboard auxiliary device PS2
0065-006A SSGA, undocumented PS2
006B SSGA, RAM enable/remap PS2
006C-006F SSGA, undocumented PS2
0070 AT CMOS write internal register
0071 AT CMOS read internal register
0070-0071 CMOS real-time clock, NMI mask PS2
0070-007F CMOS real-time clock, NMI mask AT
0074-0076 reserved PS2
0800-008F SSGA DMA page registers PS2
0080-009F DMA page registers, 74LS612 AT
0090 central arbitration control port (Micro Channel)
0091 card selected feedback (Micro Channel)
0092 system control port A (Micro Channel)
0093 reserved (Micro Channel)
0094 system board setup (Micro Channel)
0096 POS "CD SETUP" selector (Micro Channel)
00A0-00A1 Interrupt controller 2, 8259A AT PS2
00A0-00AF IOSGA NMI mask register PS2
00B0-00BF realtime clock/calendar, (undocumented) PS2
00C0-00DF reserved PCjr PC XT AT CVT M30
00C0-00CF DOS ROM register, Toshiba 1000
00D0-00EF "special" register, Toshiba 1000
00C0 0C1 key register, Toshiba 1000
00C1 keyboard transfer register, Toshiba 1000
00C2 keyboard receive register, Toshiba 1000
00C3 keyboard status register, Toshiba 1000
00C8 DOS ROM page register, Toshiba 1000
00E0 CPU speed control, Toshiba 1000
00E1 keyboard status/0E2 key register, Toshiba 1000
00E2 work register, Toshiba 1000
00E3 0E4 key register, Toshiba 1000
00E4 system control register 0, Toshiba 1000
00E4 Weitek ABACUS NDP - bit 0=1, ABACUS is present
00E5 0E6 key register, Toshiba 1000
00E6 system control register 1, Toshiba 1000
00EE EMS unit index, Toshiba 1000
00EF EMS unit data, Toshiba 1000
00C0-00DF DMA controller 2, 8237A-5 AT PS2
00E0-00EF realtime clock/calendar (undocumented) M30 PS2
00F0-00FF PS/2 math coprocessor I/O (Model 50+) (diskette IO on PCjr)
0100-0101 PS/2 POS adapter ID response (Micro Channel)
0102-0107 PS/2 POS adapter configuration response (Micro Channel)
01F0-01F8 hard disk AT PS2
0200-0201 game-control adapter (joystick)
0200-020F game controller PC AT
0208-0209 Chips & Technology CS8221 chipset default EMS ports
alternate addresses: 218h, 258h, 268h, 2A8h, 2B8h, 2E8h
0208-020F Toshiba 1000 - EMS unit I/O #1
020C-020D reserved by IBM
0210-0217 expansion box (PC, XT)
0218-021F Toshiba 1000 - EMS unit I/O #2
021F reserved by IBM
0258-025F Toshiba 1000 - EMS unit I/O #3
0258-0259 LIM EMS 3.1 (not defined in 3.2+)
0268-026F Toshiba 1000 - EMS unit I/O #4
0278-027F parallel printer port 2 AT
0278-027B parallel printer port 3 PS2
02A2 clock chip in early Sperry PCs
02A8-02AF Toshiba 1000 - EMS unit I/O #5
02B8-02BF Toshiba 1000 - EMS unit I/O #6
02B0-02DF EGA (alternate) PC AT
02C0-02DF Toshiba 1000 - realtime clock
02E1 GPIB (adapter 0) AT
02E2-02E3 data acquisition (adapter 0) AT
02E8 "industry standard" COM4
02E8-02EF Toshiba 1000 - EMS unit I/O #7
02F8-02FF serial communications (COM2) PC AT PS2
0300-031F prototype card PC AT
0300-031F Leading Edge Model D clock -------------------
0320-032F hard disk controller PC
0320 Perstor HD controller, primary -------------------
0324 Perstor HD controller, secondary -------------------
0340 Sony CD-ROM -------------------
0348-0357 DCA 3278
0360-0367 PC Network (low address)
0368-036F PC Network (high address) AT
0370 Colorado Memory external tape backup control port -------
some "second controller" floppy cards -------------------
0378-037F parallel printer port PC AT
0378-037B parallel printer port PS2
0380-038F Eicon Technology Network Adapter (X.25) board (default)
0380-038F SDLC, bi-synchronous 2 PC AT
0380-0389 BSC communications (alternate) PC
0390-039F Eicon Technology Network Adapter (X.25) board (alternate)
0390-0393 cluster (adapter 0) PC AT
03A0-03A9 BSC communications (primary) PC AT
03B0-03BF monochrome/parallel printer adapter PC AT
03B4-03B5 video subsystem PS2
03BA video subsystem PS2
03BC-03BF parallel printer port 1 PS2
03C0-03CF Enhanced Graphics Adapter
03C0-03DA video subsystem and DAC PS2
03DA video status register AT&T 6300, Olivetti PC
03D0-03DF CGA, MCGA, VGA adapter control
03DE video mode selector register AT&T 6300, Olivetti PC
03E8h "industry standard" COM3
03F0-03F7 floppy disk controller PC AT PS2
03F0 Colorado Memory internal tape backup control port -------
03F2 DTK high-density XT floppy controller (output only)
03F5 DTK high-density XT floppy controller
03F8-03FF serial communications (COM1) PC AT PS2
06E2-06E3 data acquisition (adapter 1) AT
0790-0793 cluster (adapter 1) PC AT
0878 Compaq 386SX VGA BIOS relocation AT
0AE2-0AE3 data acquisition (adapter 2) AT
0B90-0B93 cluster (adapter 2) PC AT
0EE2-0EE3 data acquisition (adapter 3) AT
1390-1393 cluster (adapter 3) PC AT
22E1 GPIB (adapter 1)
2390-2393 cluster (adapter 4) PC AT
4258 LIM EMS 3.1 (not defined in 3.2+) -------------------
42E1 GPIB (adapter 2) AT
62E1 GPIB (adapter 3) AT
8258 LIM EMS 3.1 (not defined in 3.2+) -------------------
82E1 GPIB (adapter 4) AT
A2E1 GPIB (adapter 5) AT
C258 LIM EMS 3.1 (not defined in 3.2+) -------------------
C2E1 GPIB (adapter 6) AT
E2E1 GPIB (adapter 7) AT
note 1) IOSGA = I/O Support Gate Array
SSGA = System Support Gate Array
2) I/O Addresses, hex 000 to 0FF, are reserved for the system board I/O.
Hex 100 to 3FF are available on the I/O channel.
3) These are the addresses decoded by the current set of adapter cards.
IBM may use any of the unlisted addresses for future use.
4) SDLC Communication and Secondary Binary Synchronous Communications
cannot be used together because their port addresses overlap.
Reserved Memory Locations ............................................. 2**5
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 000-3FF - 1k DOS interrupt vector table, 4 byte vectors for ints 00h-0FFh.
� 30:00 - used as a stack area during POST and bootstrap routines. This
퀃o 3F:FF stack area may be revectored by an application program.
쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� ** The BIOS Data Area ** addresses from 400h to 4FFh
쳐컴컴쩡컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿪ddr.� size � description
쳐컴컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
�40:00� word � COM1 port address | These addresses are zeroed out in the
�40:02� word � COM2 port address | OS/2 DOS Compatibility Box if any of
�40:04� word � COM3 port address | the OS/2 COMxx.SYS drivers are loaded.
�40:06� word � COM4 port address |
�40:08� word � LPT1 port address
�40:0A� word � LPT2 port address
�40:0C� word � LPT3 port address
�40:0E� word � LPT4 port address (not valid in PS/2 machines)
�40:0E� word � PS/2 pointer to 1k extended BIOS Data Area at top of RAM
�40:10� word � equipment flag (see int 11h)
읕컴컴좔컴컴컴� bits:
� 0 0 no floppy drive present
� 1 if floppy drive present (see bits 6&7)
� 1 0 no math coprocessor installed
� 1 if 80x87 installed (not valid in PCjr)
� 2,3 system board RAM (not used on AT or PS/2)
� 0,0 16k 0,1 32k
� 1,0 48k 1,1 64k
� 4,5 initial video mode
� 0,0 no video adapter
� 0,1 40 column color (PCjr default)
� 1,0 80 column color
� 1,1 MDA
� 6,7 number of diskette drives
� 0,0 1 drive 0,1 2 drives
� 1,0 3 drives 1,1 4 drives
� 8 0 DMA present
� 1 DMA not present (PCjr, Tandy 1400, Sanyo 55x)
� 9,A,B number of RS232 serial ports
� C game adapter (joystick)
� 0 no game adapter
� 1 if game adapter
� D serial printer (PCjr only)
� 0 no printer
� 1 serial printer present
旼컴컴켸 E,F number of parallel printers installed
쿻ote 1) The IBM PC and AT store the settings of the system board
읕컴� switches or CMOS RAM setup information (as obtained by the BIOS
� in the Power-On Self Test (POST)) at addresses 40:10h and
� 40:13h. 00000001b indicates "on", 00000000b is "off".
旼컴컴쩡컴컨컴�
�40:12� byte � reserved (PC, AT)
읕컴컴좔컴컴컴� number of errors detected by infrared keyboard link (PCjr)
旼컴컴쩡컴컴컴� POST status (Convertible)
�40:13� word � availible memory size in Kbytes (less display RAM in PCjr)
쳐컴컴탠컴컴컴� this is the value returned by int 12h
�40:15� word � reserved
�40:17� byte � keyboard flag byte 0 (see int 9h)
읕컴컴좔컴컴컴� bit 7 insert mode on 3 alt pressed
� 6 capslock on 2 ctrl pressed
� 5 numlock on 1 left shift pressed
旼컴컴쩡컴컴컴� 4 scrollock on 0 right shift pressed
�40:18� byte � keyboard flag byte 1 (see int 9h)
읕컴컴좔컴컴컴� bit 7 insert pressed 3 ctrl-numlock (pause) toggled
� 6 capslock pressed 2 PCjr keyboard click active
� 5 numlock pressed 1 PCjr ctrl-alt-capslock held
旼컴컴쩡컴컴컴� 4 scrollock pressed 0
�40:19� byte � storage for alternate keypad entry (not normally used)
�40:1A� word � pointer to keyboard buffer head character
�40:1C� word � pointer to keyboard buffer tail character
�40:1E�32bytes� 16 2-byte entries for keyboard circular buffer, read by int 16h
�40:3E� byte � drive seek status - if bit=0, next seek will recalibrate by
읕컴컴좔컴컴컴� repositioning to Track 0.
� bit 3 drive D bit 2 drive C
旼컴컴쩡컴컴컴� 1 drive B 0 drive A
�40:3F� byte � diskette motor status (bit set to indicate condition)
읕컴컴좔컴컴컴� bit 7 write in progress 3 motor on (floppy 3)
� 6 2 motor on (floppy 2)
� 5 1 B: motor on (floppy 1)
旼컴컴쩡컴컴컴� 4 0 A: motor on (floppy 0)
�40:40� byte � motor off counter
� � � starts at 37 and is decremented 1 by each system clock tick.
� � � motor is shut off when count = 0.
�40:41� byte � status of last diskette operation where:
읕컴컴좔컴컴컴� bit 7 timeout failure 3 DMA overrun
� 6 seek failure 2 sector not found
� 5 controller failure 1 address not found
旼컴컴쩡컴컴컴� 4 CRC failure 0 bad command
�40:42�7 bytes� NEC floppy controller chip status
�40:49� byte � Video Control Data Area 1 from 0040:0049 through 0040:0066
읕컴컴좔컴컴컴� current CRT mode (hex value)
� 00h 40x25 BW (CGA) 01h 40x25 color (CGA)
� 02h 80x25 BW (CGA) 03h 80x25 color (CGA)
� 04h 320x200 color (CGA) 05h 320x200 BW (CGA)
� 06h 640x200 BW (CGA) 07h monochrome (MDA)
쿮xtended video modes (EGA/MCGA/VGA or other)
� 08h lores,16 color 09h med res,16 color
� 0Ah hires,4 color 0Bh n/a
� 0Ch med res,16 color 0Dh hires,16 color
旼컴컴쩡컴컴컴� 0Eh hires,4 color 0Fh hires,64 color
�40:4A� word � number of columns on screen, coded as hex number of columns
읕컴컴좔컴컴컴� 20 col = 14h (video mode 8, low res 160x200 CGA graphics)
� 40 col = 28h
旼컴컴쩡컴컴컴� 80 col = 46h
�40:4C� word � screen buffer length in bytes
쳐컴컴탠컴컴컴�(number of bytes used per screen page, varies with video mode)
�40:4E� word � current screen buffer starting offset (active page)
�40:50�8 words� cursor position pages 1-8
읕컴컴좔컴컴컴� the first byte of each word gives the column (0-19, 39, or 79)
旼컴컴쩡컴컴컴� the second byte gives the row (0-24)
�40:60� byte � end line for cursor (normally 1)
�40:61� byte � start line for cursor (normally 0)
�40:62� byte � current video page being displayed (0-7)
�40:63� word � base port address of 6845 CRT controller or equivalent
쳐컴컴탠컴컴컴� for active display 3B4h=mono, 3D4h=color
�40:65� byte � current setting of the CRT mode register
�40:66� byte � current palette mask setting (CGA)
�40:67�5 bytes� temporary storage for SS:SP during shutdown (cassette interface)
�40:6C� word � timer counter low word
�40:6E� word � timer counter high word
�40:69� byte � HD_INSTALL (Columbia PCs) (not valid on most clone computers)
읕컴컴좔컴컴컴� bit 0 0 8 inch external floppy drives
� 1 5-1/4 external floppy drives
� 1,2 highest drive address which int 13 will accept
� (since the floppy drives are assigned 0-3,subtract
� 3 to obtain the number of hard disks installed)
� 4,5 # of hard disks connected to expansion controller
� 6,7 # of hard disks on motherboard controller
� (if bit 6 or 7 = 1, no A: floppy is present and
旼컴컴쩡컴컴컴� the maximum number of floppies from int 11 is 3)
�40:70� byte � 24 hour timer overflow 1 if timer went past midnight
쳐컴컴탠컴컴컴� it is reset to 0 each time it is read by int 1Ah
�40:71� byte � BIOS break flag (bit 7 = 1 means break key hit)
�40:72� word � reset flag
읕컴컴좔컴컴컴� PCjr keeps 1234h here for softboot when a cartridge is installed
� bits 1234h = soft reset, memory check will be bypassed
� 4321h = preserve memory (PS/2 only)
� 5678h = system suspended (Convertible)
� 9ABCh = manufacturing test mode (Convertible)
旼컴컴쩡컴컴컴� ABCDh = system POST loop mode (Convertible)
�40:74� byte � status of last hard disk operation ; PCjr special disk control
�40:75� byte � # of hard disks attached (0-2) ; PCjr special disk control
�40:76� byte � HD control byte; temp holding area for 6th param table entry
�40:77� byte � port offset to current hd adapter ; PCjr special disk control
�40:78�4 bytes� timeout value for LPT1,LPT2,LPT3,LPT4
�40:7C�4 bytes� timeout value for COM1,COM2,COM3,COM4 (0-0FFh secs, default 1)
�40:80� word � pointer to start of circular keyboard buffer, default 03:1E
�40:82� word � pointer to end of circular keyboard buffer, default 03:3E
읕컴컴좔컴컴컴� note: early Zenith Z183 BIOS set these pointers to zero and
旼컴컴쩡컴컴컴� ignored them.
�40:84� .... � Video Control Data Area 2, 0040:0084 through 0040:008A
�40:84� byte � rows on the screen minus 1 (EGA only)
�40:84� byte � PCjr interrupt flag; timer channel 0 (used by POST)
�40:85� word � bytes per character (EGA only)
�40:85�2 bytes� (PCjr only) typamatic character to repeat
�40:86�2 bytes� (PCjr only) typamatic initial delay
�40:87� byte � mode options (EGA only)
읕컴컴좔컴컴컴� bit 0 0 cursor emulation in effect
� 1 no cursor emulation
� 1 0 EGA is connected to a color display
� 1 EGA is connected to monochrome TTL display
� 2 0 wait for vertical retrace (CGA active)
� 1 don't wait for vertical retrace (EGA or MDA active)
� 3 0 EGA is the active display,
� 1 "other" display is active.
� 4 reserved
� 5,6 EGA memory size
� 0,0 64k
� 0,1 128k
� 1,0 192k
� 1,1 256k
� 7 0 don't clear screen on mode changes
� 1 if the last "set mode" specified not to clear the
� video buffer
� mode combinations:
� bit3 bit1 Meaning
� 0 0 EGA is active display and is color
� 0 1 EGA is active display and is monochrome
� 1 0 EGA is not active, a mono card is active
旼컴컴쩡컴컴컴� 1 1 EGA is not active, a CGA is active
�40:87� byte � (PCjr only) current Fn key code
쳐컴컴탠컴컴컴� 80h bit indicates make/break key code?
�40:88� byte � feature bits and switches (EGA only) 0=on, 1=off
읕컴컴좔컴컴컴� bit 0 switch 1
� 1 switch 2
� 2 switch 3
� 3 switch 4
旼컴컴쩡컴컴컴� 4-7 feature bits
�40:88� byte � (PCjr only) special keyboard status byte
읕컴컴좔컴컴컴� bit 7 function flag 3 typamatic (0=enable,1=disable)
� 6 Fn-B break 2 typamatic speed (0=slow,1=fast)
� 5 Fn pressed 1 extra delay bef.typamatic (0=enable)
旼컴컴쩡컴컴컴� 4 Fn lock 0 write char, typamatic delay elapsed
�40:89� byte � (PCjr) current value of 6845 reg 2 (horizontal synch) used by
읕컴컴좔컴컴컴� ctrl-alt-cursor screen positioning routine in ROM
� (VGA)
� bit 0 reserved
� 1 video summing enabled
� 2 0 for color monitor attached
� 1 for mono monitor
� 3 0 for default palette loading enabled
� 4 0 for 8x8 text font
� 1 for 8x16 text font
旼컴컴쩡컴컴컴� 5-7 reserved
�40:8A� byte � (PCjr) CRT/CPU Page Register Image, default 3Fh
읕컴컴좔컴컴컴� (VGA) Display Combination Code Index. This is the value
� set/returned by function 1Ah of the Video BIOS. This byte
� contains an index into the ROM BIOS Display Combination Code
� table, which is a list of byte pairs that specify valid
� combinations of one or two video subsystems. Video subsystems
� are designated by the following values:
� 00h no display
� 01h MDA with monochrome display
� 02h CGA with color display
� 03h reserved
� 04h EGA with color display
� 05h EGA with monochrome display
� 06h Professional Graphics Adapter
� 07h VGA with analog monochrome display
� 08h VGA with analog color display
� 09h reserved
� 0Ah MCGA with digital color display
� 0Bh MCGA with analog monochrome display
� 0Ch MCGA with analog color display
旼컴컴쩡컴컴컴� 0FFh unrecognized video subsystem
�40:8B� byte � last diskette data rate selected
읕컴컴좔컴컴컴� bit 7,6 starting data transfer rate to use
� 0,0 500 kb/sec
� 0,1 300 kb/sec
� 1,0 250 kb/sec
� 1,1 reserved
� 5,4 last step rate selected
� 3 ending data transfer rate to use
� 2 reserved
� 1 reserved
� 0 1 combination floppy/fixed disk controller detected
� 0 XT floppy only controller (for 360kb drive) detected
� Data Transfer Rates
� Kbits/sec Media Drive Sectors/Track
� 250 360k 360k 9
� 300 360k 1.2M 9
� 500 1.2M 1.2M 15
� 250 720k 720k 9
� 250 720k 1.4M 9
旼컴컴쩡컴컴컴� 500 1.4M 1.4M 18
�40:8C� byte � hard disk status returned by controller
�40:8D� byte � hard disk error returned by controller
�40:8E� byte � hard disk interrupt (bit 7=working interrupt)
�40:8F� byte � combo_card - status of drives 0 and 1
읕컴컴좔컴컴컴� bit 7 reserved
� 6 drive type determined for drive 1
� 5 drive multiple data rate capability for drive 1
� 0 no multiple data rate
� 1 multiple data rate
� 4 1 then drive 1 has 80 tracks
� 0 then drive 1 has 40 tracks
� 3 reserved
� 2 drive type determined for drive 0
� 1 drive multiple data rate capability for drive 0
� 0 no multiple data rate
� 1 multiple data rate
� 0 1 the drive 0 has 80 tracks
旼컴컴쩡컴컴컴� 0 the drive 0 has 40 tracks
�40:90�4 bytes� media state drive 0, 1, 2, 3
읕컴컴좔컴컴컴� floppy_media_state
� bit 7,6 Data transfer rate
� 00 - 500 K/sec
� 01 - 300 K/sec
� 10 - 250 K/sec
� 11 - reserved
� 5 double stepping required
� 4 media/drive determined
� 3 reserved
� 2-0 present state
� 000 360k in 360k unestablished
� 001 360k in 1.2M unestablished
� 010 1.2M in 1.2M unestablished
� 011 360k in 360k established
� 100 360k in 1.2M established
� 101 1.2M in 1.2M established
� 110 reserved
旼컴컴쩡컴컴컴� 111 none of the above
�40:94�2 bytes� track currently seeked to drive 0, 1
�40:96� byte � keyboard flag byte 3 (see int 9h)
�40:97� byte � keyboard flag byte 2 (see int 9h)
�40:98� dword � segment:offset pointer to users wait flag
�40:9C� dword � users timeout value in microseconds
�40:A0� byte � real time clock wait function in use
읕컴컴좔컴컴컴� bits 7 wait time elapsed and posted flag
� 6-1 reserved
旼컴컴쩡컴컴컴� 0 int 15h, function 86h (WAIT) has occurred
�40:A1� byte � LAN A DMA channel flags
�40:A2�2 bytes� status LAN A 0,1
�40:A4� dword � saved hard disk interrupt vector
�40:A8� dword � SAVE_PTR: EGA pointer to table of 7 parameters in segment:
읕컴컴좔컴컴컴� offset format. Format of table:
� D_1 dword pointer to 1472 byte table of 64 video parameters
� D_2 dword reserved
� D_3 dword reserved
� D_4 dword reserved
� D_5 dword reserved for future use
� D_6 dword reserved for future use
旼컴컴쩡컴컴컴� D_7 dword reserved for future use
�40:B0�2 words� international support (Tandy 1000 TX)
�40:B4� byte � keyboard NMI control flags (Convertible)
�40:B4� byte � monochrome monitor hookup detect (Tandy 1000 TX)
� � � 00h not present 0FFh present
�40:B5� dword � keyboard break pending flags (Convertible)
�40:B5� byte � extended equipment detect (5 bits) (Tandy 1000 TX)
읕컴컴좔컴컴컴� bit 0 = 0 drive A is 5�
� 1 drive A is 3�
� 1 = 0 drive A is 5�
� 1 drive A is 3�
� 2 = 0 Tandy 1000 keyboard layout
� 1 IBM keyboard layout
� 3 = 0 CPU slow mode
� 1 CPU fast mode
� 4 = 0 internal color video support enabled
� 1 internal color video support disabled, external
� video enabled (chg from mb'd to expansion card)
� 5 = 0 no external monochrome video installed
旼컴컴쩡컴컴컴� 1 external monochrome video installed
�40:B6� byte � extended equipment detect (1 bit) (Tandy 1000 TX)
읕컴컴좔컴컴컴� bit 0 = 0 drive C is 5�
旼컴컴쩡컴컴컴� 1 drive C is 3�
�40:B9� byte � port 60 single byte queue (Convertible)
�40:BA� byte � scan code of last key (Convertible)
�40:BB� byte � pointer to NMI buffer head (Convertible)
�40:BC� byte � pointer to NMI buffer tail (Convertible)
�40:BD�16bytes� NMI scan code buffer (Convertible)
�40:CE� word � day counter (Convertible and after)
� to � -04:8F� end of BIOS Data Area
쳐컴컴좔컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� ** End of BIOS Data Area **
쳐컴컴쩡컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
�40:90�-40:EF � reserved by IBM
�40:F0�16bytes� Inter-Application Communications Area (for use by applications
�40:FF� � to transfer data or parameters to each other)
읕컴컴좔컴컴컴� 1) Used by Turbo Power's FMARK (mark memory for TSRs).
� 2) Used by Norton Utilities' TimeMark to store the time.
� 3) Used by BRIEF editor.
旼컴컴쩡컴컴컴�
�50:00� byte � DOS print screen status flag
읕컴컴좔컴컴컴� 00h not active or successful completion
� 01h print screen in progress
旼컴컴쩡컴컴컴� 0FFh error during print screen operation
�50:01� � Used by BASIC
�50:02-03 � PCjr POST and diagnostics work area
�50:04� byte � Single drive mode status byte - not used by AT&T DOS 2.11!
읕컴컴좔컴컴컴� 00 logical drive A was last active
旼컴컴컴컴컴컴� 01 logical drive B was last active
�50:05-0E � PCjr POST and diagnostics work area
�50:0F� � BASIC: SHELL flag (set to 02h if there is a current SHELL)
�50:10� word � BASIC: segment address storage (set with DEF SEG)
�50:12�4 bytes� BASIC: int 1Ch clock interrupt vector segment:offset storage
�50:16�4 bytes� BASIC: int 23h ctrl-break interrupt segment:offset storage
�50:1A�4 bytes� BASIC: int 24h disk error int vector segment:offset storage
�50:1B-1F � Used by BASIC for dynamic storage
�50:20-21 � Used by DOS for dynamic storage
�50:22-2C � Used by DOS for diskette parameter table. See int 1Eh for values
읕컴컴좔컴컴컴� In DOS 1.0 this is located in the ROM BIOS, but in DOS 1.1 and
� subsequent it is a part of DOS located at 05:22. The first byte
� (out of eleven) of the Disk Parameter contains the hexadecimal
� value CF in DOS 1.0 and DF in DOS 1.1 and later.
� DOS 1.0 24ms
旼컴컴컴컴컴컴� DOS 1.1 26ms
�50:30-33 � Used by MODE command
�50:81� � number of floppies installed in the system?
�50:82� � first hard disk drive?
�50:83� � last hard disk drive?
�50:34-FF � Unknown - Reserved for DOS
읕컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
Absolute Addresses .................................................... 2**6
0008:0047 IO.SYS or IBMBIO.COM IRET instruction. This is the dummy routine that
interrupts 01h, 03h, and 0Fh are initialized to during POST.
C000:001E EGA BIOS signature (the letters IBM)
F000:FA6E table of characters 00h-7Fh used by int 10h video BIOS
The first 128 characters are stored here and each occupies 8 bytes.
The high bit ones are somewhere on the video adapter card.
F000:FFF5 BIOS release date
F000:FFFE PC model identification
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� ROM BIOS � model byte �
� copyright � � submodel byte machine �
� date � � � revision �
쳐컴컴컴컴컵컴컴탠컴컵컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � 00 � 00 � 00 � AT&T 6300, Olivetti PC �
� 09/02/86 � FA � 00 � 00 � PS/2 Model 30 �
� 01/10/86 � FB � 00 � 00 � XT-2 (early) �
� 01/10/86 � FB � 00 � 01 � XT Model 089 �
� 05/09/86 � FB � 01 � 02 � XT-2 (revised) �
� 01/10/84 � FC � -- � -- � AT Model 099 (original) �
� 06/10/85 � FC � 00 � 01 � AT Model 239 6mHz (6.6 max governor) �
� 11/15/85 � FC � 01 � 00 � AT Model 339, 339 8mHz (8.6 max governor) �
� � FC � 01 � 00 � Compaq 386/16 �
� � FC � 01 � 03 � some Phoenix 386 BIOS �
� � FC � 01 � 81 � some Phoenix 386 BIOS �
� 04/21/86 � FC � 02 � 00 � XT/286 �
� 02/13/87 � FC � 04 � 00 � PS/2 Model 50 �
� 02/13/87 � FC � 05 � 00 � PS/2 Model 60 �
� � FC � 00 � � 7531/2 Industrial AT �
� � FC � 06 � � 7552 "Gearbox" �
� 04/18/88 � FC � 04 � 03 � PS/2 50Z �
� 01/24/90 � FC � 01 � 00 � Compaq Deskpro 80386/25e �
� 10/02/89 � FC � 02 � 00 � Compaq Deskpro 386s, 386SX, 16mHz �
� 06/01/83 � FD � -- � -- � PCjr �
� 11/08/82 � FE � -- � -- � XT, Portable PC, XT/370, 3270PC �
� 04/24/81 � FF � -- � -- � PC-0 (16k motherboard) �
� 10/19/81 � FF � -- � -- � PC-1 (64k motherboard) �
� 08/16/82 � FF � -- � -- � PC, XT, XT/370 (256k motherboard) �
� 10/27/82 � FF � -- � -- � PC, XT, XT/370 (256k motherboard) �
� ? 1987 � F8 � 00 � 00 � PS/2 Model 80 �
� 3/30/87 � F8 � 00 � 00 � PS/2 Model 80-041 16mHz �
� 08/28/87 � F8 � ?? � ?? � PS/2 Model 80-071 16mHz �
� ? 1987 � F8 � 01 � 00 � PS/2 Model 80 20mHz �
� 09/17/87 � F8 � 01 � 01 � PS/2 Model 80-111 20mHz �
� ? � F8 � 04 � ? � PS/2 Model 70-121 �
� 01/18/89 � F8 � 0B � 00 � PS/2 Model 70 Portable �
� 04/11/88 � F8 � 09 � 02 � PS/2 Model 70 desktop �
� 02/20/89 � F8 � 0D � � PS/2 Model 70-A21 �
� 09/13/85 � F9 � 00 � 00 � Convertible �
� � 2D � -- � -- � Compaq PC (4.77mHz original) �
� � 9A � -- � -- � Compaq Plus (XT compatible) �
읕컴컴컴컴컨컴컴좔컴컨컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The IBM PC System Interrupts (Overview) ............................... 2**7
The interrupt table is stored in the very lowest location in memory, starting
at 0000:0000h. The locations are offset from segment 0, i.e. location 0000h has
the address for int 0, etc. The table is 1024 bytes in length and contains 256
four byte vectors from 00h to 0FFh. Each address' location in memory can be
found by multiplying the interrupt number by 4. For example, int 7 could be
found by (7x4=28) or 1Bh (0000:001Bh).
These interrupt vectors normally point to ROM tables or are taken over by DOS
when an application is run. Some applications revector these interrupts to
their own code to change the way the system responds to the user. DOS provides
int 21h function 25h to change interrupts from a high level; altering the
interrupt vector table directly is not recommended, nor would it really get
you anywhere.
Quick Chart of Interrupts 00h-0FFh .................................... 2**8
旼컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커
� Interrupt Address � �
쳐컴컴컴쩡컴컴컴쩡컴컴� Function �
� Number� (Hex) � Type �
쳐컴컴컴탠컴컴컴탠컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0 � 00-03 � CPU � Divide by Zero �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 1 � 04-07 � CPU � Single Step �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 2 � 08-0B � CPU � Nonmaskable �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 3 � 0C-0F � CPU � Breakpoint �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 4 � 10-13 � CPU � Overflow �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 5 � 14-17 � BIOS� Print Screen �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 6 � 18-1B � hdw � Reserved �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 7 � 1C-1F � hdw � Reserved �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 8 � 20-23 � hdw � Time of Day �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 9 � 24-27 � hdw � Keyboard �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� A � 28-2B � hdw � Reserved �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� B � 2C-2F � hdw � Communications (8259) �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� C � 30-33 � hdw � Communications �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� D � 34-37 � hdw � Disk �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� E � 38-3B � hdw � Diskette �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� F � 3C-3F � hdw � Printer �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 10 � 40-43 � BIOS� Video �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 11 � 44-47 � BIOS� Equipment Check �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 12 � 48-4B � BIOS� Memory �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 13 � 4C-4F � BIOS� Diskette/Disk �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 14 � 50-53 � BIOS� Serial Communications �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 15 � 54-57 � BIOS� Cassette, System Services �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 16 � 58-5B � BIOS� Keyboard �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 17 � 5C-5F � BIOS� Parallel Printer �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 18 � 60-63 � BIOS� ROM BASIC Loader �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 19 � 64-67 � BIOS� Bootstrap Loader �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 1A � 68-6B � BIOS� Time of Day �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 1B � 6C-6F � BIOS� Keyboard Break �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 1C � 70-73 � BIOS� Timer Tick �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 1D � 74-77 � BIOS� Video Initialization �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 1E � 78-7B � BIOS� Diskette Parameters �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 1F � 7C-7F � BIOS� Video Graphics Characters, second set �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 20 � 80-83 � DOS � General Program Termination �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 21 � 84-87 � DOS � DOS Services Function Request �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 22 � 88-8B � DOS � Called Program Termination Address �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 23 � 8C-8F � DOS � Control Break Termination Address �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 24 � 90-93 � DOS � Critical Error Handler �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 25 � 94-97 � DOS � Absolute Disk Read �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 26 � 98-9B � DOS � Absolute Disk Write �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 27 � 9C-9F � DOS � Terminate and Stay Resident �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 28-3F � A0-FF � DOS � Reserved for DOS �
읕컴컴컴좔컴컴컴좔컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� *29h Fast Screen Write �
� *2Ah Microsoft Networks - Session Layer Interrupt �
� 2Fh Multiplex Interrupt �
� *30h Far jump instruction for CP/M-style calls �
� 33h Used by Microsoft Mouse Driver �
旼컴컴컴쩡컴컴컴쩡컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 40-43 �100-115� BIOS� Reserved for BIOS �
읕컴컴컴좔컴컴컴좔컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 40h Hard Disk BIOS �
� 41h Hard Disk Parameters (except PC1) �
� 42h Pointer to screen BIOS entry (EGA, VGA, PS/2) �
� 43h Pointer to EGA initialization parameter table �
旼컴컴컴쩡컴컴컴쩡컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 44 �116-119� BIOS� First 128 Graphics Characters �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 45-47 �120-131� BIOS� Reserved for BIOS �
읕컴컴컴좔컴컴컴좔컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 45h Reserved by IBM (not initialized) �
� 46h Pointer to hard disk 2 params (AT, PS/2) �
� 47h Reserved by IBM (not initialized) �
旼컴컴컴쩡컴컴컴쩡컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 48 �132-135� BIOS� PCjr Cordless Keyboard Translation �
쳐컴컴컴탠컴컴컴탠컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 49 �136-139� BIOS� PCjr Non-Keyboard Scancode Translation Table �
읕컴컴컴좔컴컴컴좔컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 4Ah Real-Time Clock Alarm (Convertible, PS/2) �
旼컴컴컴쩡컴컴컴쩡컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 50-5F �140-17F� BIOS� Reserved for BIOS �
읕컴컴컴좔컴컴컴좔컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 5Ah Cluster Adapter BIOS entry address �
� *5Bh IBM (cluster adapter?) �
� 5Ch NETBIOS interface entry port �
旼컴컴컴쩡컴컴컴쩡컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 60-67 �180-19F� User Program Interrupts (availible for general use) �
읕컴컴컴좔컴컴컴좔컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 60h 10-Net Network �
� 67h Used by LIM & AQA EMS, EEMS �
旼컴컴컴쩡컴컴컴쩡컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 68-7F �1A0-1FF� Reserved by IBM �
읕컴컴컴좔컴컴컴좔컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 6Ch System Resume Vector (Convertible) �
� 6Fh some Novell and 10-Net API functions �
� 70h IRQ 8, Real Time Clock Interrupt (AT, PS/2) �
� 71h IRQ 9, LAN Adapter 1 �
� 72h IRQ 10 (AT, XT/286, PS/2) Reserved �
� 73h IRQ 11 (AT, XT/286, PS/2) Reserved �
� 74h IRQ 12 Mouse Interrupt (PS/2) �
� 75h IRQ 13, Coprocessor Error �
� 76h IRQ 14, Hard Disk Controller (AT, PS/2) �
� 77h IRQ 15 (AT, XT/286, PS/2) Reserved �
� 7Ch IBM REXX88PC command language �
旼컴컴컴쩡컴컴컴쩡컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 80-85 �200-217� ROM BASIC �
쳐컴컴컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 86-F0 �218-3C3� Used by BASIC Interpreter When BASIC is running �
쳐컴컴컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� F1-FF �3C4-3FF� Reserved by IBM �
읕컴컴컴좔컴컴컴좔컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� *0F8h Set Shell Interrupt (OEM) �
� *0F9h OEM SHELL service codes �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The IBM-PC System Interrupts (in detail) .............................. 2**9
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 00h Divide by Zero �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0000h) (processor error). Automatically called at end of DIV or IDIV
operation that results in error. Normally set by DOS to display an
error message and abort the program.
note On an 8086/8088, the return address points to the following instruction
On an 80286/80386, the return address points to the divide instruction
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 01h Single step �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0004h) Taken after every instruction when CPU Trap Flag indicates
single-step mode (bit 8 of FLAGS is 1). This is what makes the "T"
command of DEBUG work for single stepping. Is not generated after MOV
to segment register or POP of segment register. (unless you have a
very early 8088 with the microcode bug).
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쿔nterrupt 02h Non-maskable interrupt �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0008h) Vector not disabled via CLI. Generated by NMI signal in
hardware. This function is called in the event of a memory
parity error or may occur in the event of other hardware
problems or failures depending on the specific manufacturer's
hardware. Displays the appropriate error message and halts the
processor.
Some AT chip sets apparently use int 02h to signal I/O errors
as well as parity errors.
This signal has various uses:
POST parity error: all except PCjr and Convertible
80x87 coprocessor interrupt: all except PCjr and Convertible
Keyboard interrupt: PCjr, Convertible
I/O channel check: Convertible, PS/2 50+
Disk controller power-on request: Convertible
System suspend: Convertible
Realtime clock: Convertible
System watchdog timer: PS/2 50+
Timeout interrupt: PS/2 50+
DMA timer time-out interrupt: PS/2 50+
Infrared keyboard link: PCjr
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쿔nterrupt 03h Breakpoint �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:000Ch) Taken when CPU executes the 1-byte int 3 (0CCh). Similar to 8080's
(internal) RST instruction. Generally used to set breakpoints for DEBUG.
note 1) Also used by Turbo Pascal versions 1,2,3 when {$U+} specified.
2) Int 3s are sometimes inserted by the Microsoft Linker in response to
an unresolved symbol.
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쿔nterrupt 04h Divide overflow �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0010h) Generated by INTO instruction if OF flag is set. If flag is not set,
(internal) INTO is effectively a NOP. Used to trap any arithmetic errors when
program is ready to handle them rather than immediately when they
occur.
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쿔nterrupt 05h Print Screen �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0014h) Service dumps the screen to the printer. Invoked by int 9 for shifted
key 55 (PrtSc). Automatically called by keyboard scan when PrtSc key
is pressed. Normally executes a routine to print the screen, but may
call any routine that can safely be executed from inside the keyboard
handler. Status and result byte are at address 0050:0000.
(internal) BOUND Check Failed (80286+)
Generated by BOUND instruction when the value to be tested is less
than the indicated lower bound or greater than the indicated upper
bound.
entry AH 05h
return absolute address 50:0
00h print screen has not been called, or upon return from a call
there were no errors
01h print screen is already in progress
0FFh error encountered during printing
note 1) Uses BIOS services to read the screen.
2) Output is directed to LPT1.
3) Revectored into GRAPHICS.COM if GRAPHICS.COM is loaded.
4) On the Tandy 1000TX this interrupt can be enabled or disabled across
the expansion slots via a DIP switch.
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쿔nterrupt 06h Reserved by IBM �
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(0:0018h)
On the Tandy 1000TX this interrupt can be enabled or disabled across
the expansion slots via a DIP switch.
(internal) Undefined Opcode (80286+)
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쿔nterrupt 07h Reserved by IBM �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:00C0h)
On the Tandy 1000TX this interrupt can be enabled or disabled across
the expansion slots via a DIP switch.
(internal) No Math Unit Available (80286+)
note The 80286 and later can be programmed to generate an int 7 whenever
an ESC instruction is encountered. This could be used to emulate an
80x87 series coprocessor in software and be transparent to the
application software. It could also be used to make a non-Intel
floating point processor emulate an 80x87.
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쿔nterrupt 08h Timer �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0020h) 55ms timer "tick" issued 18.2 times per second.
(IRQ0) 8259-1 Interrupt Controller
Updates the system time at [0040:006C] (low word) and [0040:006E]
(high word) and issues an int 1Ch (timer). (int 1Ch points to an
IRET instruction unless changed by a resident program). The timer
interrupt is given the highest maskable interrupt priority upon
power up.
(internal) Double Fault (80286+ protected mode) Called when multiple exceptions
occur on one instruction, or an exception occurs in an exception
handler. If an exception occurs in the double fault handler, the CPU
goes into SHUTDOWN mode (which circuitry in the PC/AT converts to a
reset).
entry AH 08h
return absolute addresses:
40:6C number of interrupts since power on (4 bytes)
40:70 number of days since power on (1 byte)
40:67 day counter on all products after AT
40:40 motor control count - gets decremented and shuts off diskette
motor if zero
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쿔nterrupt 09h Keyboard �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0024h) Taken whenever a key is pressed or released. This is normally a scan
(IRQ1) code, but may also be an ACK or NAK of a command on AT-type
keyboards. The hardware provides the key pressed in a non-ASCII scan
code format read at I/O port 60h. The servicer acknowledges receipt
of the key by toggling bit 7 of port 61h. (Port 61h should be read
first, then bit 7 ORed on, output to port 61h, then ANDed off, and
resent to port 61h).
The read key is decoded to yield an ASCII character, special
function key (such as F1) or a control function like Left Shift Key.
The converted ASCII character is placed into the next available
position in the circular queue keyboard. It is put in the position
indicated by queue tail when it will not cause the loss of earlier
entered data. The queue head points to the oldest key pressed in the
buffer which has not been removed from the queue (the normal process
uses int 16h to remove keys from the queue and return the key value
to the int 16h caller).
The 16 word queue holds up to 16 keys. If the queue head equals the
queue tail, the queue is empty. Valid keys in the queue comprise
the upper byte scan code and the lower byte ASCII character. If the
key pressed has no ASCII equivalent (i.e F1 to F12), the lower byte
is zero.
Toggle and shift keys are not placed in the buffer, but appear in
the two status bytes at absolute addr. [0040:0017,18].
Special key combinations will cause other events to occur:
a) Ctrl-Alt_Del - Reset computer by jumping to power_on_reset
b) Print screen - Call int_5_prn_scrn to print the current screen
c) Ctrl-Break - Call int_1Bh control break key processor (DOS)
d) Pause - Wait until an ASCII key is pressed, without
placing the key in the queue
(internal) Math Unit Protection Fault (80286+ protected mode)
entry AH 09h
return at absolute memory addresses:
40:17 bit
0 right shift key depressed
1 left shift key depressed
2 control key depressed
3 alt key depressed
4 ScrollLock state has been toggled
5 NumLock state has been toggled
6 CapsLock state has been toggled
7 insert state is active
40:18 bit
0 left control key depressed
1 left alt key depressed
2 SysReq key depressed
3 Pause key has been toggled
4 ScrollLock key is depressed
5 NumLock key is depressed
6 CapsLock key is depressed
7 Insert key is depressed
40:96 bit
0 last code was the E1h hidden code
1 last code was the E0h hidden code
2 right control key down
3 right alt key down
4 101 key Enhanced keyboard installed
5 force NumLock if rd ID & kbx
6 last character was first ID character
7 doing a read ID (must be bit 0)
40:97 bit
0 ScrollLock indicator
1 NumLock indicator
2 CapsLock indicator
3 circus system indicator
4 ACK received
5 resend received flag
6 mode indicator update
7 keyboard transmit error flag
40:1E keyboard buffer (20h bytes)
40:1C buffer tail pointer
40:72 1234h if ctrl-alt-del pressed on keyboard
AL scan code
note 1) Int 05h invoked if PrtSc key pressed.
2) Int 1Bh invoked if Ctrl-Break key sequence pressed.
3) Int 15h, AH=85h invoked on AT and after if SysReq key is pressed.
4) Int 15h, AH=4Fh invoked on machines after AT.
5) Int 16h, BIOS keyboard functions, uses this interrupt.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 0Ah EGA Vertical Retrace �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0028h) used by EGA vertical retrace
(IRQ2) 8259-1 Interrupt Controller
note 1) The TOPS and PCnet adapters use this IRQ line by default.
2) On systems equipped with 2 interrupt controller chips (8259), IRQ 2
is used to support the second interrupt controller. In this case,
int 71h (IRQ 9) is used to replace IRQ 2. Hardware calls to int 71h
are redirected to this interrupt to maintain compatibility.
3) Many VGA boards to not use this interrupt.
(internal) Invalid Task State Segment (80286+ protected mode)
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쿔nterrupt 0Bh Communications Controller (serial port) hdw. entry �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:002Ch) Serial Port 2 (COM2) 8259-1
(IRQ3)
note 1) IRQ 3 may be used by SDLC (synchronous data-link control) or
bisynchronous communications cards instead of a serial port.
2) The TOPS and PCnet adapters use this interrupt request line as an
alternate.
3) On PS/2s, COM2 through COM8 share this IRQ.
4) For most serial boards, COM4 shares this IRQ.
5) On the Commodore Amiga 2000 with the PC Bridge Board, this interrupt
is used for communication between the Amiga system board and the
Bridge Board. This was probably the lowest IRQ level they felt safe
using, but limits the A2000's use of network cards, etc.
6) This interrupt is used by part of the stack-switching code added
to DOS 3.2 for use with Local Area Network adapters.
7) The PS/2 puts COM3 through COM8 at port addresses above 3FFh (not
properly decoded by older PCs) and has all of them sharing IRQ3.
(internal) Not Present (80286+ protected mode)
Generated when loading a segment register if the segment descriptor
indicates that the segment is not currently in memory. May be used
to implement virtual memory.
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쿔nterrupt 0Ch Communications Controller (serial port) Hardware Entry �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0030h) Serial Port 1 (COM1) or internal modem in PCjr or Convertible
(IRQ4) 8259-1
note 1) IRQ 4 may be used by SDLC (synchronous data-link control) or
bisynchronous communications cards instead of a serial port.
2) On some PCs, this interrupt is shared by COM3.
3) Tandy computers use IRQ4 instead of IRQ5 for the hard disk interrupt.
4) Best performance of mice sometimes happens when they are configured
for IRQ4 instead of IRQ3, since some mouse drivers may lock system
interrupts for long periods.
(internal) Stack Fault (80286+ protected mode)
Generated on stack overflow/underflow. Note that the 80286 will shut
down in real mode if SP=1 before a push.
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쿔nterrupt 0Dh Hard Disk �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0034h) Miscelleneous uses
(IRQ5) 8259-1
note 1) Various Tandy 1000 models may use this line for the 60Hhz RAM refresh
or as "optional bus interrupt."
2) Used by hard disk on IBM XT and most compatibles.
3) LPT2 on AT, XT/286, and PS/2
4) Dummy CRT vertical retrace on PCjr
(internal) General Protection Violation (80286+)
Called in real mode when an instruction attempts to access a word
operand located at offset 0FFFFh or a PUSH MEM or POP MEM
instruction contains an invalid bit code in the second byte, or
when an instruction exceeds the maximum length allowed (10 bytes
for 80286, 15 bytes for 80386)
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쿔nterrupt 0Eh Diskette Interrupt �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0038h) Generated by floppy controller on completion of an operation
(IRQ6) (sets bit 8 of 40:3E)
(internal) Page Fault (80386+ native mode)
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쿔nterrupt 0Fh Reserved by IBM �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:003Ch) IRQ7 used by 8259 PPI interrupt (LPT1, LPT2)
(IRQ7)
note 1) Generated by the LPT1 printer adapter when printer becomes ready. Many
printer adapters do not reliably generate this interrupt.
2) This interrupt is normally avoided. If a bad interrupt occurs, it will
vector to this spot (when caused by a misprogrammed 8259 PIC)
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
C H A P T E R T H R E E
THE PC ROM BIOS
C O N T E N T S
Calling the ROM BIOS .................................................. 3**1
Interrupt 10h Video Services ......................................... 3**2
Interrupt 11h Equipment Check ........................................ 3**3
Interrupt 12h Memory Size ............................................ 3**4
Interrupt 13h Disk Functions ......................................... 3**5
Interrupt 14h Initialize and Access Serial Port ...................... 3**6
FOSSIL Drivers ......................................... 3**7
Interrupt 15h Cassette I/O ........................................... 3**8
Interrupt 16h Keyboard I/O ........................................... 3**9
Interrupt 17h Printer ................................................ 3**10
Interrupt 18h ROM BASIC .............................................. 3**11
Interrupt 19h Bootstrap Loader ....................................... 3**12
Interrupt 1Ah Time of Day ............................................ 3**13
Interrupt 1Bh Control-Break .......................................... 3**14
Interrupt 1Ch Timer Tick ............................................. 3**15
Interrupt 1Dh Vector of Video Initialization Parameters .............. 3**16
Interrupt 1Eh Vector of Diskette Controller Parameters ............... 3**17
Interrupt 1Fh Ptr to Graphics Character Extensions (Graphics Set 2) .. 3**18
The ROM BIOS is the lowest level of software access. It contains the
following routines:
(all)
power-on self-test (POST)
boostrap loader
clock
floppy disk I/O
video I/O
keyboard
serial ports
parallel ports
print screen
equipment check
report memory size
(AT)
hard disk I/O
report memory size (extended memory)
extended memory block moves
enhanced video and keyboard I/O
high resolution timer
alarm
Machines such as the PC Convertible, PCjr, and non-IBM machines add
additional functions.
Calling the ROM BIOS .................................................. 3**1
The BIOS services are invoked by placing the number of the desired function in
register AH, subfunction in AL, setting the other registers to any specific
requirements of the function, and invoking any of ints 10h through int 1Fh.
The original IBM PC Technical Reference gave the absolute addresses of the
ROM routines. Some early software jumped directly to these addresses, with
mixed results on non-IBM BIOSes. This practice was common on machines
predating the PC, but there is no practical use for it now. The OS/2
Compatibility Box also does not support jumping directly into the ROM.
When the interrupt is called, all register and flag values are pushed into the
stack. The interrupt address contains a pointer into an absolute address in the
ROM BIOS chip address space. This location may be further vectored into the
IBMBIO.COM (or equivalent) file or user file.
The address vector points to a particular BIOS command handler. The handler
pops the register values, compares them to its list of functions, and executes
the function if valid. When the function is complete, it may pass values back
to the command handler. The handler will push the values into the stack and
then return control to the calling program.
Most functions will return an error code; some return more information.
Details are contained in the listings for the individual functions.
Register settings listed are the ones used by the BIOS. Some functions will
return with garbage values in unused registers. Do not test for values in
unspecified registers; your program may exhibit odd behavior.
Three sets of BIOS routines are available: PC BIOS, AT BIOS (also called
CBIOS or "Old compatibility BIOS", and the PS/2 ABIOS "Advanced BIOS".
The Advanced BIOS is contained in PS/2 ROMs. It is primarily intended for OS
use rather than application use. OS/2 can take advantage of ABIOS routines to
reduce RAM use on PS/2 systems. The ABIOS can be replaced by disk and RAM based
ABIOS code if desired. There is a new BIOS Data Area defined in high memory
that occupies one K of RAM. In OS/2 systems, parts of the ABIOS are replaced
by OS/2 drivers.
While the CBIOS must be addressed via pointers, the routines in the ABIOS are
fixed in absolute locations so they can be referenced directly by OS/2.
The ABIOS can run in protected mode, and is fully reentrant. It supports three
types of function requests - single staged, discrete multistaged, or continuous
multistaged. A single-staged request does its job immediately and returns
control to the caller. A discrete multistaged request may happen in two or more
stages with pauses between the stages. The caller may regain control during the
pauses. A continuous multistaged request starts a staged operation that never
ends. (sometimes called a daemon).
Unlike the CBIOS which is called with software interrupts, ABIOS is accessed
with FAR calls. ABIOS calls are completely reentrant in both real and
protected modes. To call an ABIOS function, the calling program must pass
pointers to two data structures - a request block and a common data area. The
request block specifies the desired function number and the common data area is
a table that contains pointers to all the ABIOS' other tables and data areas.
The common data area's internal structure contains the function transfer
tables which have the addresses of the BIOS routines.
ABIOS stack frame and calling conventions:
bytes stack contents
2 common data area pointer (segment/selector only) required
4 request block pointer - required
4 function transfer table pointer - furnished by ABIOS or caller
4 device block pointer - furnished by ABIOS or caller
4 return address
In ABIOS Transfer Convention, only the first two items are required. ABIOS
assigns the second two. In Operating System Transfer Convention, the caller
provides the second two. Since the parameters are not removed from the stack
on return to the caller, the operating system may save the function transfer
table and device addresses after they have been furnished by the ABIOS by a
call.
ABIOS does no interrupt arbitration. It assumes all interrupts are handled by
the caller or the OS and it is called only for service. If more than one
device is sharing a hardware interrupt, the OS must determine which interrupt
is valid for the ABIOS.
OS/2 may use the ABIOS if found, but otherwise duplicates the BIOS calls for
the DOS Compatibility Box by vectoring BIOS calls into its own device drivers.
This makes it rather difficult for DOS drivers for mass storage, high
resolution video boards, multitasking APIs using int 15h, etc. If your
software needs to manipulate hardware directly you might want to check if your
code is running under OS/2. The simplest method is to check for DOS version 10
or higher.
note Some references list an "XT/2" machine, which was reputedly an 8mHz
8088 with 640k and a clock on the motherboard. IBM doesn't list such
a machine, and I have a late '86 XT, one of the last made. It is
pretty much like the older ones.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 10h Video Services 3**2 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0040h) The BIOS Video Services may be found in Chapter 16.
(internal) Coprocessor Error (80286+)
Generated by the CPU when the -ERROR pin is asserted by the coprocessor
(usually 80x87, but may be any multimaster CPU or alternate NDP such
as Weitek, etc.). ATs and clones usually wire the coprocessor to use
IRQ13, but not all get it right.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 11h Equipment Check 3**3 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0044h) Reads the BIOS Data Area and returns two bytes of setup info.
entry no parameters are required
return AX Equipment listing word. Bits are:
0 number of floppy drives
0 no drives
1 bootable (IPL) diskette drive installed
1 math chip
0 no math coprocessor (80x87) present
1 math coprocessor (80x87) present
(PS/2) 2 0 mouse not installed
1 mouse installed
(PC) 2,3 system board RAM
0,0 16k (PC-0, PC-1)
0,1 32k
1,0 48k
1,1 64k (PC-2, XT)
note 1) not commonly used. Set both bits to 1
2) both bits always 1 in AT
4,5 initial video mode
0,0 no video installed (use with dumb terminal)
0,1 40x25 color (CGA)
1,0 80x25 color (CGA, EGA, PGA, MCGA, VGA)
1,1 80x25 monochrome (MDA or Hercules, most super-
hires mono systems)
6,7 number of diskette drives (only if bit 0 is 1)
0,0 1 drives
0,1 2 drives
1,0 3 drives
1,1 4 drives
8 0 DMA present
1 no DMA (PCjr, some Tandy 1000s, 1400LT)
9,A,B number of RS232 serial ports (0-3)
0,0,0 none
0,0,1 1
0,1,0 2
0,1,1 3
1,0,0 4
C 0 no game I/O attached
1 game I/O attached (default for PCjr)
D serial accessory installation
0 no serial accessories installed
1 Convertible - internal modem installed
or PCjr - serial printer attached
E,F number of parallel printers
0,0 none
0,1 one (LPT1, PRN)
1,0 two (LPT2)
1,1 three (LPT3)
note Models before PS/2 would allow a fourth
parallel printer. Remapping of the BIOS in the
PS/2s does not allow the use of LPT4.
(386 extended AX)
23d 0 Weitek ABACUS - virtual '86 EMS page tables
not correctly initialized
1 Weitek ABACUS - virtual '86 EMS page tables OK
24d 0 Weitek ABACUS NDP not present
1 Weitek ABACUS NDP present
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 12h Memory Size 3**4 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0048h) get system memory
entry no parameters required
return AX number of contiguous 1K RAM blocks available for DOS
note 1) This is the same value stored in absolute address 04:13h.
2) For some early PC models, the amount of memory returned by this call is
determined by the settings of the dip switches on the motherboard and
may not reflect all the memory that is physically present.
3) For the PC/AT, the value returned is the amount of functional memory
found during the power-on self-test, regardless of the memory size
configuration information stored in CMOS RAM.
4) The value returned does not reflect any extended memory (above the 1 Mb
boundary) that may be present on 80286 or 80386 machines.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 13h Disk Functions 3**5 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0049h) The service calls for BIOS disk functions are located in
Chapter 8.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 14h Initialize and Access Serial Port For Int 14 3**6 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
Note: Some IBM PS/2 Model 50Z machines were delivered with serial ports
that did not meet specification. Some cheap clone serial ports may
also be troublesome.
(0:0050h) the following status is defined:
serial status byte:
bits 0 delta clear to send
1 delta data set ready
2 trailing edge ring detector
3 delta receive line signal detect
4 clear to send
5 data set ready
6 ring indicator
7 receive line signal detect
line status byte:
bits 0 data ready
1 overrun error
2 parity error
3 framing error
4 break detect
5 transmit holding register empty
6 transmit shift register empty
7 time out note: if bit 7 set then other bits are invalid
Though present on the IBM PS/2s, COM3 and COM4 are not widely
standardized across the industry. The most common definitions are:
port addr. IRQ interrupt
COM1 3F8 IRQ4 int 0Ch
COM2 2F8 IRQ3 int 0Bh
COM3 3E8 IRQ4 int 0Ch
COM4 2E8 IRQ3 int 0Bh
As you can see, COM1/COM3 and COM2/COM4 are siamesed. Since the ISA
bus does not support shared interrupts, simultaneous access of two of
a pair may cause conflict. For example, a mouse and a modem would not
coexist well on paired ports.
All routines have AH=function number and DX=RS232 card number (0 based).
AL=character to send or received character on exit, unless otherwise noted.
entry AH 00h Initialize And Access Serial Communications Port
bit pattern: BBBPPSLL
BBB = baud rate: 110,150,300,600,1200,2400,4800,9600
PP = parity: 01 = odd, 11 = even
S = stop bits: 0 = 1, 1 = 2
LL = word length: 10 = 7-bits, 11 = 8-bits
AL parms for initialization:
bit pattern:
0 word length
1 word length
2 stop bits
3 parity
4 parity
5 baud rate
6 baud rate
7 baud rate
word length 10 7 bits
11 8 bits
stop bits 0 1 stop bit
1 2 stop bits
parity 00 none
01 odd
11 even
baud rate 000 110 baud
001 150 baud
010 300 baud
011 600 baud
100 1200 baud
101 2400 baud
110 4800 baud
111 9600 baud (4800 on PCjr)
DX port number (0=COM1, 1=COM2, etc.)
return AH line status
AL modem status
note To initialize the serial port to > 9600 baud on PS/2 machines, see
fns 04h and 05h.
Function 01h Send Character in AL to Comm Port
entry AH 01h
AL character
DX port number (0 - 3)
return AH RS232 status code
bit 0 data ready
1 overrun error
2 parity error
3 framing error
4 break detected
5 transmission buffer register empty
6 transmission shift register empty
7 timeout
AL modem status
bit
0 delta clear-to-send
1 delta data-set-ready
2 trailing edge ring detected
3 change, receive line signal detected
4 clear-to-send
5 data-set-ready
6 ring received
7 receive line signal detected
Function 02h Wait For A Character From Comm Port DX
entry AH 02h
DX port number (0-3)
return AL character received
AH error code (see above)(00h for no error)
Function 03h Fetch the Status of Comm Port DX (0 or 1)
entry AH 03h
DX port (0-3)
return AH set bits (01h) indicate comm-line status
bit 7 timeout
bit 6 empty transmit shift register
bit 5 empty transmit holding register
bit 4 break detected ("long-space")
bit 3 framing error
bit 2 parity error
bit 1 overrun error
bit 0 data ready
AL set bits indicate modem status
bit 7 received line signal detect
bit 6 ring indicator
bit 5 data set ready
bit 4 clear to send
bit 3 delta receive line signal detect
bit 2 trailing edge ring detector
bit 1 delta data set ready
bit 0 delta clear to send
Function 04h Extended Initialize (Convertible, PS/2)
entry AH 04h
AL break status
01h if break
00h if no break
BH parity
00h no parity
01h odd parity
02h even parity
03h stick parity odd
04h stick parity even
BL number of stop bits
00h one stop bit
01h 2 stop bits (1� if 5 bit word length)
CH word length
00h 5 bits
01h 6 bits
02h 7 bits
03h 8 bits
CL baud rate
00h 110
01h 150
02h 300
03h 600
04h 1200
05h 2400
06h 4800
07h 9600
08h 19200
DX comm port (0-3)
return AH line control status
AL modem status
note Provides a superset of fn 00h capabilities for PS/2 machines.
Function 05h Extended Communication Port Control (Convertible, PS/2)
entry AH 05h
AL 00h read modem control register
01h write modem control register
BL modem control register
bits 0 DTR data terminal ready
1 RTS request to send
2 out1
3 out2
4 loop
5,6,7 reserved
DX port number (0=COM1, 1=COM2, etc.)
return AH port status (see 00h above)
AL modem status (see 00h above)
BL modem control register (see 01h above)
FOSSIL Drivers ........................................................ 3**7
Interrupt 14h FOSSIL (Fido/Opus/Seadog Standard Interface Level) drivers
A FOSSIL is a device driver for handling the IBM PC serial
com?232 status code (see AH=00h above)
AL ASCII value of character received from serial port
note Will timeout if DSR is not asserted, even if function 03h returns
data ready.
entry AH 03h FOSSIL: Request status
DX port number (NOP if DX=00FFh)
return AX status bit mask
AH bit 0 set RDA input data is available in buffer
1 set OVRN input buffer overrun
2 N/A
3 N/A
4 N/A
5 set THRE room is available in output buffer
6 set TSRE output buffer is empty
7 N/A
AL bit 0 N/A
1 N/A
2 N/A
3 set this bit is always set
4 N/A
5 N/A
6 N/A
7 set DCD carrier detect
note Bit 3 of AL is always returned set to enable programs to use it as a
carrier detect bit on hardwired (null modem) links.
entry AH 04h Initialize FOSSIL driver
BX 4F50h (optional)
DX port number (DX=00FFh special)
ES:CX pointer to ^C flag address (optional)
return AX 1954h if successful
BL maximum function number supported (excluding 7Eh-0BFh)
BH revision of FOSSIL supported
note 1) DTR is raised when FOSSIL inits.
2) Existing baudrate is preserved.
3) If BX contains 4F50h, the address specified in ES:CX is that of a ^C
flag byte in the application program, to be incremented when ^C is
detected in the keyboard service routines. This is an optional service
and only need be supported on machines where the keyboard service can't
(or won't) perform an int 1Bh or int 23h when a control-C is entered.
entry AH 05h Deinitialize FOSSIL driver
DX port number (DX=00FFh special)
return none
note 1) DTR is not affected.
2) Disengages driver from comm port. Should be done when operations on the
port are complete.
3) If DX=00FFh, the initialization that was performed when FOSSIL function
04h with DX=00FFh should be undone.
entry AH 06h FOSSIL: Raise/lower DTR
AL DTR state to be set
00h lower DTR
01h raise DTR
DX comm port (NOP if DX=00FFh)
return none
entry AH 07h FOSSIL: Return timer tick parameters
return AH ticks per second on interrupt number shown in AL
AL timer tick interrupt number (not vector!)
DX milliseconds per tick (approximate)
entry AH 08h FOSSIL: Flush output buffer
DX port number (NOP if DX=00FFh)
return none
note Waits until all output is done.
entry AH 09h FOSSIL: Purge output buffer
DX port number (NOP if DX=00FFh)
return none
note Returns to caller immediately.
entry AH 0Ah FOSSIL: Purge input buffer
DX port number (NOP if DX=00FFh)
return none
note 1) If any flow control restraint has been employed (dropping RTS or
transmitting XOFF) the port will be "released" by doing the reverse,
raising RTS or sending XON.
2) Returns to caller immediately.
entry AH 0Bh FOSSIL: Transmit no wait
AL ASCII character value to be sent
DX port number (NOP if DX=00FFh)
return AX 0000h character not accepted
0001h character accepted
note This is exactly the same as the "regular" transmit call except that if
there is no space available in the output buffer a value of zero is
returned in AX, if room is available a value 1 (one) is returned.
entry AH 0Ch FOSSIL: Nondestructive Read no Wait
DX port number (NOP if DX=00FFh)
return AH character
0FFFFh character not available
note 1) Reads async buffer.
2) Does not remove keycode from buffer.
entry AH 0Dh FOSSIL: Keyboard read no wait
return AX IBM keyboard scan code or
0FFFFh if no keyboard character available
note 1) Use IBM-style function key mapping in the high order byte.
2) Scan codes for non function keys are not specifically required but may
be included.
3) Does not remove keycode from buffer.
entry AH 0Eh FOSSIL: Keyboard input with wait
return AX IBM keyboard scan code
note Returns the next character from the keyboard or waits if no character
is available.
entry AH 0Fh Enable or Disable flow control
AL bit mask describing requested flow control
bits 0 XON/XOFF on transmit (watch for XOFF while sending)
1 CTS/RTS (CTS on transmit/RTS on receive)
2 reserved
3 XON/XOFF on receive (send XOFF when buffer near full)
4-7 not used, FOSSIL spec calls for setting to 1
DX port number (NOP if DX=00FFh)
return none
note 1) Bit 2 is reserved for DSR/DTR, but is not currently supported in any
implementation.
2) TRANSMIT flow control allows the other end to restrain the transmitter
when you are overrunning it. RECEIVE flow control tells the FOSSIL to
attempt to do just that if it is being overwhelmed.
3) Enabling transmit Xon/Xoff will cause the FOSSIL to stop transmitting
upon receiving an Xoff. The FOSSIL will resume transmitting when an Xon
is received.
4) Enabling CTS/RTS will cause the FOSSIL to cease transmitting when CTS
is lowered. Transmission will resume when CTS is raised. The FOSSIL
will drop RTS when the receive buffer reaches a predetermined
percentage full. The FOSSIL will raise RTS when the receive buffer
empties below the predetermined percentage full. The point(s) at which
this occurs is left to the individual FOSSIL implementor.
5) Enabling receive Xon/Xoff will cause the FOSSIL to send a Xoff when the
receive buffer reaches a pre-determined percentage full. An Xon will be
sent when the receive buffer empties below the predetermined percentage
full. The point(s) at which this occurs is left to the individual
FOSSIL implementor.
6) Applications using this function should set all bits ON in the high
nibble of AL as well. There is a compatible (but not identical) FOSSIL
driver implementation that uses the high nibble as a control mask. If
your application sets the high nibble to all ones, it will always work,
regardless of the method used by any given driver.
entry AH 10h Extended Ctrl-C/Ctrl-K checking and transmit on/off
AL flags bit mask byte (bit set if activated)
bits 0 enable/disable Ctrl-C/Ctrl-K checking
1 disable/enable the transmitter
2-7 not used
DX port number (NOP if DX=00FFh)
return AX status byte
0000h control-C/K has not been received
0001h control-C/K has been received
note This is used primarily for programs that can't trust XON/XOFF at FOSSIL
level (such as BBS software).
entry AH 11h FOSSIL: Set current cursor location.
DH row (line) 0-24
DL column 0-79
return none
note 1) This function looks exactly like the int 10h, fn 02h on the IBM PC.
The cursor location is passed in DX: row in DH and column in DL. This
function treats the screen as a coordinate system whose origin (0,0) is
the upper left hand corner of the screen.
2) Row and column start at 0.
entry AH 12h FOSSIL: Read current cursor location.
return DH row (line)
DL column
note 1) Looks exactly like int 10h/fn 03h in the IBM PC BIOS. The current
cursor location (same coordinate system as function 16h) is passed back
in DX.
2) Row and column start at 0.
entry AH 13h FOSSIL: Single character ANSI write to screen.
AL value of character to display
return none
note This call might not be reentrant since ANSI processing may be through
DOS.
entry AH 14h FOSSIL: Enable or disable watchdog processing
AL 00h to disable watchdog
01h to enable watchdog
DX port number (NOP if DX=00FFh)
return none
note 1) This call will cause the FOSSIL to reboot the system if Carrier Detect
for the specified port drops while watchdog is turned on.
2) The port need not be active for this function to work.
entry AH 15h Write character to screen using BIOS support routines
AL ASCII code of character to display
return none
note 1) This function is reentrant.
2) ANSI processing may not be assumed.
entry AH 16h Insert or Delete a function from the timer tick chain
AL 00h to delete a function
01h to add a function
ES:DX address of function
return AX 0000h successful
0FFFFh unsuccessful
entry AH 17h FOSSIL: Reboot system
AL boot type
00h cold boot
01h warm boot
return none
entry AH 18h FOSSIL: Read block
CX maximum number of characters to transfer
DX port number (NOP if DX=00FFh)
ES:DI pointer to user buffer
return AX number of characters transferred
note 1) This function does not wait for more characters to become available if
the value in CX exceeds the number of characters currently stored.
2) ES:DI are left unchanged by the call; the count of bytes actually
transferred will be returned in AX.
entry AH 19h FOSSIL: Write block
CX maximum number of characters to transfer
DX port number (NOP if DX=00FFh)
ES:DI pointer to user buffer
return AX number of characters transfered
note ES and DI are not modified by this call.
entry AH 1Ah FOSSIL: Break signal begin or end
AL 00h stop sending 'break'
01h start sending 'break'
DX port number (NOP if DX=00FFh)
return none
note 1) Resets all transmit flow control restraints such as an XOFF received
from remote.
2) Init (fn 04h) or UnInit (fn 05h) will stop an in-progress break.
3) The application must determine the "length" of the break.
entry AH 1Bh FOSSIL: Return information about the driver
CX size of user buffer in bytes
DX port number (if DX=00FFh, port data will not be valid)
ES:DI pointer to user buffer
return AX number of characters transferred
ES:DI user buffer structure:
00h word size of structure in bytes
02h byte FOSSIL driver version
03h byte revision level of this specific driver
04h dword FAR pointer to ASCII ID string
08h word size of the input buffer in bytes
0Ah word number of bytes in input buffer
0Ch word size of the output buffer in bytes
0Eh word number of bytes in output buffer
10h byte width of screen in characters
11h byte screen height in characters
12h byte actual baud rate, computer to modem
(see mask in function 00h
note 1) The baud rate byte contains the bits that fn 00h would use to set the
port to that speed.
2) The fields related to a particular port (buffer size, space left in the
buffer, baud rate) will be undefined if port=0FFh or an invalid port is
contained in DX.
3) Additional information will always be passed after these, so that the
fields will never change with FOSSIL revision changes.
entry AH 7Eh FOSSIL: Install an external application function
AL code assigned to external application
ES:DX pointer to entry point
return AX 1954h FOSSIL driver present
not 1954h FOSSIL driver not present
BH 00h failed
01h successful
BL code assigned to application (same as input AL)
note 1) Application codes 80h-0BFh are supported. Codes 80h-83h are reserved.
2) An error code of BH=00h with AX=1954h should mean that another external
application has already been installed with the code specified in AL.
3) Applications are entered via a FAR call and should make a FAR return.
entry AH 7Fh FOSSIL: Remove an external application function
AL code assigned to external application
ES:DX pointer to entry point
return AX 1954h
BH 00h failed
01h successful
BL code assigned to application (same as input AL)
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 15h Cassette I/O 3**8 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0054h) 1) Renamed "System Services" on PS/2 line.
2) Issuing int 15h on an XT may cause a system crash.
On AT and after, interrupts are disabled with CLI when the
interrupt service routine is called, but most ROM versions do
not restore interrupts with STI.
3) For the original IBM PC, int 15h returns AH=80h and CF set for
all calls with AH not 0,1, or 2.
4) For the PC/XT int 15h returns AH=86h, CF set if called at all.
(the PC/XT ROM BIOS does not support int 15h)
5) For the AT/339, int 15h returns AH=86h, CF set if called with
an invalid function code.
Function 00h Turn Cassette Motor On (PC, PCjr only)
entry AH 00h
return CF set on error
AH error code
00h no errors
01h CRC error
02h bad tape signals
no data transitions (PCjr)
03h no data found on tape
not used (PCjr)
04h no data
no leader (PCjr)
80h invalid command
86h no cassette present
not valid in PCjr
note NOP for systems where cassette not supported.
Function 01h Turn Cassette Motor Off (PC, PCjr only)
entry AH 01h
return CF set on error
AH error code (86h)
note NOP for systems where cassette not supported.
Function 02h Read Blocks From Cassette (PC, PCjr only)
entry AH 02h
CX number of bytes to read
ES:BX segment:offset + 1 of last byte read
return CF set on error
AH error code (01h, 02h, 04h, 80h, 86h)
DX count of bytes actually read
ES:BX pointer past last byte written
note 1) NOP for systems where cassette not supported.
2) Cassette operations normally read 256 byte blocks.
Function 03h Write Data Blocks to Cassette (PC, PCjr only)
entry AH 03h
CX count of bytes to write
ES:BX pointer to data buffer
return CF set on error
AH error code (80h, 86h)
CX 00h
ES:BX pointer to last byte written+1
note 1) NOP for systems where cassette not supported.
2) The last block is padded to 256 bytes with zeroes if needed.
3) No errors are returned by this service.
Function 0Fh ESDI Format Unit Periodic Interrupt (PS/2 50+)
entry AH 0Fh
AL phase code
00h reserved
01h surface analysis
02h formatting
return CF clear if formatting should continue
set if it should terminate
note 1) Called the BIOS on the ESDI Fixed Disk Drive Adapter/A during a format
or surface analysis operation after each cylinder is completed.
2) This function call can be captured by a program so that it will be
notified as each cylinder is formatted or analyzed. The program can
count interrupts for each phase to determine the current cylinder
number.
3) The BIOS default handler for this function returns with CF set.
Function 10h TopView API Function Calls (TopView)
see Chapter 17
Function 20h PRINT.COM (DOS 3.1+ internal) (AT, XT/286, PS/2 50+)
entry AH 20h
AL subfunction
00h disable critical region flag
01h set critical region flag
ES:BX pointer to flag byte set while inside DOS calls
10h set up SysReq routine
11h completion of SysReq routine (software only)
Function 21h Read Power-On Self Test (POST) Error Log (PS/2 50+)
entry AH 21h
AL 00h read POST log
01h write POST log
BH device ID
BL device error code
return CF set on error
AH status
00h successful read
BX number of POST error codes stored
ES:DI pointer to error log
01h list full
80h invalid command
86h function unsupported
note The log is a series of words, the first byte of which identifies the
error code and the second is the device ID.
Function 40h Read/Modify Profiles (Convertible)
entry AH 40h
AL 00h read system profile in CX,BX
01h write system profile from CX, BX
02h read internal modem profile in BX
03h write internal modem profile from BX
BX profile info
return BX internal modem profile (from 02h)
CX,BX system profile (from 00h)
Function 41h Wait On External Event (Convertible)
entry AH 41h
AL condition type
bits 0-2 condition to wait for
0,0,0 any external event
0,0,1 compare and return if equal
0,1,0 compare and return if not equal
0,1,1 test and return if not zero
1,0,0 test and return if zero
3 reserved
4 0 user byte
1 port address
5-7 reserved
BH condition compare or mask value
condition codes:
00h any external event
01h compare and return if equal
02h compare and return if not equal
03h test and return if not zero
04h test and return if zero
BL timeout value times 55 milliseconds
00h if no time limit
DX I/O port address (if AL bit 4=1)
ES:DI pointer to user byte (if AL bit 4=0)
Function 42h Request System Power Off (Convertible)
entry AH 42h
AL 00h to use system profile
01h to force suspend regardless of profile
return unknown
Function 43h Read System Status (Convertible)
entry AH 43h
return AL status byte
bit 0 LCD detached
1 reserved
2 RS232/parallel powered on
3 internal modem powered on
4 power activated by alarm
5 bad time
6 external power in use
7 battery low
Function 44h (De)activate Internal Modem Power (Convertible)
entry AH 44h
AL 00h to power off
01h to power on
return unknown
Function 4Fh OS Hook - Keyboard Intercept (except PC, PCjr, and XT)
entry AH 4Fh
AL scan code, CF set
return AL scan code
CF set processing desired
clear scan code should not be used
note 1) Called by int 9 handler for each keystroke to translate scan codes.
2) An OS or a TSR can capture this function to filter the raw keyboard
data stream. The new handler can substitute a new scan code, return the
same scan code, or return the carry flag clear causing the keystroke to
be discarded. The BIOS default routine simply returns the scan code
unchanged.
3) A program can call int 15h/fn0C0h to determine whether the host
machine's BIOS supports keyboard intercept.
4) Used internally by PC-MOS/386 v4.00+ for keyboard input.
5) Some BIOSes do not properly support this call. However, some versions
of KEYB.COM provide additional 4Fh support.
Function 52h MicroSoft RAM-Resident Software Specification 1.0
This standard was proposed by MicroSoft in 1986 as a common
interface for TSR programs. It appears to have been largely
unknown or disregarded.
Function 0: Get Program Information by Name
entry DS:BX The Program ID of the memory-resident program to look for
return AL 0FFh if the program we are looking for is installed
00h if it is not installed
CX The number of this program. The first program installed is
number 0, with the second program being number 1, etc. By using
a dynamic numbering system, we avoid conflicts between programs
that might otherwise choose the same ID. We also provide a good
way to scan all the resident programs using function 1.
ES:DX pointer to the Program ID Record (PIDR)
note This function tests to see if a program is memory resident and returns
a pointer to its program information if it is resident. To use this
function, set DS:BX to point to the program ID. Each installed program
will check to see if this program ID agrees with its own internal
program ID.
Function 1: Get Program Information by Number
entry CX Number of the program we want the information for
return AL 0FFh if the program we are looking for is installed
00h if it is not installed
ES:DX pointer to the Program ID Record (PIDR)
note This function returns exactly the same information as function 0. The
only difference is how we identify the program we want, which is
determined by its position in the interrupt chain; program 0 is the
last program in the chain, and the first program in the chain (usually
the most recently installed) has the highest number.
Function 2: Activate Program
entry CX The number of the program we want to activate
DS:BX Activation Record. This record will give program information on
how and what it should activate within the program
return none
note This function activates one of the installed programs. It is useful
if you want to control many desk accessories with a single control
panel like the one used in SideKick. You can also use it with a
program like ProKey to run a named macro under program control, or
with SideKick to bring up one of the desk accessories from within a
program or batch file.
Function 3: Deactivate Program
entry CX The number of the program we want to deactivate
DS:BX Deactivation Record. This record will give program information
on how and what it should deactivate within the program
return none
note This function is the opposite of function 2 (activate program).
Function 4: Enable Program
entry CX The number of the program we want to enable
DS:BX Enable mask record. This mask describes what features we want
to enable. A null record enables all the features.
return none
note This function is the opposite of function 5 (disable program).
Function 5: Disable Program
entry CX The number of the program we want to disable
DS:BX Disable mask record. This mask describes what features we want
to disable. A null record disables all the features.
return none
note Sometimes it becomes necessary to disable a program to prevent it from
conflicting with another program, this function is designed to do that.
This function is the opposite of function 4 (Enable Program).
Function 70h EEROM handler (Tandy 1000HX)
entry AH 00h read from EEROM
BL 00h
01h write to EEROM
BL word number to write (0-15)
DX word value to write
return DX (AH=00h) word value
CF set on error (system is not a Tandy 1000 HX)
Function 80h OS Hook - Device Open (AT, XT/286, PS/2)
entry AH 80h
BX device ID
CX process ID
return CF set on error
AH status
note 1) Acquires ownership of a logical device for a process.
2) This call, along with fns 81h and 82h, defines a simple protocol that
can be used to arbitrate usage of devices by multiple processes. A
multitasking program manager would be expected to capture int 15h and
provide the appropriate service.
3) The default BIOS routine for this function simply returns with CF clear
and AH=00h.
Function 81h Device Close (AT, XT/286, PS/2)
entry AH 81h
BX device ID
CX process ID
return CF set on error
AH status
note 1) Releases ownership of a logical device for a process.
2) A multitasking program manager would be expected to capture int 15h and
provide the appropriate service.
3) The BIOS default routine for this function simply returns with the CF
clear and AH=00h.
Function 82h Program Termination (AT, XT/286, PS/2)
AH 82h
BX device ID
return CF set on error
AH status
note 1) Closes all logical devices opened with function 80h.
2) A multitasking program manager would be expected to capture int 15h and
provide the appropriate service.
3) The BIOS default routine for this function simply returns with CF clear
and AH=00h.
Function 83h Event Wait (AT, XT/286, Convertible, PS/2 50+)
entry AH 83h
AL 00h to set interval
01h to cancel
CX:DX number of microseconds to wait (granularity is 976 microseconds)
ES:BX pointer to semaphore flag (bit 7 is set when interval expires)
(pointer is to caller's memory) (some sources list bit 15 set)
return CF clear OK
set function already busy
note 1) Requests setting of a semaphore after a specified interval or cancels a
previous request.
2) The calling program is responsible for clearing the semaphore before
requesting this function.
3) The actual duration of an event wait is always an integral multiple of
976 microseconds. The CMOS date/clock chip interrupts are used to
implement this function.
4) Use of this function allows programmed, hardware-independent delays at
a finer resolution than can be obtained through use of the MS-DOS Get
Time function (int 21h/fn 2Ch) which returns time in hundredths of a
second.
5) CX:DX is a four-byte integer.
7) This function is called by int 70h and is not the normal Int 08h/1Ch
clock tick. It is generated by the MC146818A Real Time Clock chip.
This is the battery backed up CMOS clock chip.
Function 84h Read Joystick Input Settings (AT, XT/286, PS/2)
entry AH 84h
DX 00h to read the current switch settings (return in AL)
01h to read the resistive inputs
return CF set on error
(fn 00h)
AL switch settings (bits 7-4)
(fn 01h)
AX stick A (X) value
BX stick A (Y) value
CX stick B (X) value
DX stick B (Y) value
note 1) An error is returned if DX does not contain a valid subfunction number.
2) If no game adapter is installed, all returned values are 00h.
3) Using a 250K Ohm joystick, the potentiometer values usually lie within
the range 0-416 (0000h-01A0h).
Function 85h System Request (SysReq) Key Pressed (except PC, PCjr, XT)
entry AH 85h
AL 00h key pressed
01h key released
return CF set on error
AH error code
note 1) Called by BIOS keyboard decode routine when the SysReq key is detected.
2) The BIOS handler for this call is a dummy routine that always returns a
success status unless called with an invalid subfunction number in AL.
3) A multitasking program manager would be expected to capture int 15h so
that it can be notified when the user strikes the SysReq key.
Function 86h Delay (except PC, PCjr, XT)
AH 86h
CX:DX 4-byte integer, number of microseconds to wait
CX high word, DX low word
return CF clear after wait elapses
CF set immediately due to error
note 1) Suspends the calling program for a specified interval in microseconds.
2) The actual duration of the wait is always an integral multiple of 976
microseconds.
3) Use of this function allows programmed, hardware-independent delays at
a finer resolution than can be obtained through use of the MS-DOS Get
Time function (int 21h fn 2Ch) which returns time in hundredths of a
second).
4) This function calls int 70h and is not the normal Int 08h/1Ch
clock tick. It is generated by the MC146818A Real Time Clock chip.
This is the battery backed up CMOS clock chip.
Function 87h Memory Block Move (2-3-486 machines only)
AH 87h
CX number of words to move
ES:SI pointer to Global Descriptor Table (GDT)
offset 00h-0Fh reserved, set to zero
00h null descriptor
08h uninitialized, will be made into GDT descriptor
10h-11h source segment length in bytes
(2*CX-1 or greater)
12h-14h 24-bit linear source address
15h access rights byte (always 93h)
16h-17h reserved, set to zero
18h-19h destination segment length in bytes
(2*CX-1 or greater)
1Ah-1Ch 24-bit linear destination address
1Dh access rights byte (always 93h)
1Eh-1Fh reserved, set to zero
20h *uninitialized, used by BIOS
28h *uninitialized, will be made into SS descriptor
(*) some sources say initialized to zero
return CF set on error
AH status
00h success - source copied into destination
01h RAM parity error
02h exception interrupt error
03h address line 20 gating failed
note 1) The GDT table is composed of six 8-byte descriptors to be used by the
CPU in protected mode. The four descriptors in offsets 00h-0Fh and
20h-2Fh are filled in by the BIOS before the CPU mode switch.
2) The addresses used in the descriptor table are linear (physical)
24-bit addresses in the range 000000h-0FFFFFFh - not segments and
offsets - with the least significant byte at the lowest address and the
most significant byte at the highest address.
3) Interrupts are disabled during this call; use may interfere with the
operation of comm programs, network drivers, or other software that
relies on prompt servicing of hardware interrupts.
4) This call is not valid in the OS/2 Compatibility Box.
5) This call will move a memory block from any real or protected mode
address to any other real or protected mode address.
6) DESQview does not intercept function 87, but QEXT and QEMM do, thereby
allowing function 87 to work correctly inside DV. VDISK, which uses
function 87, works inside DV. If VDISK is sitting at the 1 MB mark,
then the int 19h vector will have a VDISK signature in it. The normal
way to check for VDISK presence is by checking for the string "VDISK"
at offset 12h of the segment of the int 19h vector. If the string
matches, then you can determine how much extended memory is reserved
for VDISK by looking at offset 2Ch is the 3-byte address of the lowest
extended memory address NOT in use by VDISK (i.e. if you see at 2Ch
"00 00 14" then that means that VDISK is using memory up to 1 MB +
256K).
Function 88h Get Extended Memory Size (AT, XT/286, PS/2)
entry AH 88h
return AX number of contiguous 1K blocks of extended memory starting at
address 1024k
note 1) This call will not work in the OS/2 Compatibility Box.
2) Some BIOSes and software manipulate the Carry Flag when this function
is called. When tested on a vanilla 386 with AMI BIOS the machine
returned with the carry flag set. When 386-to-the-Max was loaded, the
flag was not set.
3) Used by IBM VDISK 4.0.
Function 89h Switch Processor to Protected Mode (AT, XT/286, PS/2)
entry AH 89h
BH interrupt number for IRQ0, written to ICW2 of 8259 PIC #1
(must be evenly divisible by 8, determines IRQ0-IRQ7)
BL interrupt number for IRQ8, written to ICW2 of 8259 PIC #2
(must be evenly divisible by 8, determines IRQ8-IRQ15)
ES:SI pointer to 8-entry Global Descriptor Table for protected mode:
offset 00h null descriptor, initialized to zero
08h GDT descriptor
10h IDT (Interrupt Descriptor Table) descriptor
18h DS, user's data segment
20h ES, user's extra segment
28h SS, user's stack segment
30h CS, user's code segment
38h uninitialized, used to build descriptor for
BIOS code segment
return CF set on error
AH 0FFh error enabling address line 20
CF clear function successful (CPU is in protected mode)
AH 00h
CS user-defined selector
DS user-defined selector
ES user-defined selector
SS user-defined selector
note 1) The user must initialize the first seven descriptors; the eighth is
filled in by the BIOS to provide addressability for its own execution.
The calling program may modify and use the eighth descriptor for any
purpose after return from this function call.
2) Intercepted by Microsoft's HIMEM.SYS and Quarterdeck's QEMM.SYS.
Function 90h Device Busy Loop (except PC, PCjr, XT)
entry AH 90h
AL predefined device type code:
00h disk (may timeout)
01h diskette (may timeout)
02h keyboard (no timeout)
03h PS/2 pointing device (may timeout)
80h network
(no timeout)
0FCh hard disk reset (PS/2) (may timeout)
0FDh diskette motor start (may timeout)
0FEh printer (may timeout)
ES:BX pointer to request block for type codes 80h through 0FFh
(for network adapters ES:BX is a pointer to network control
block)
return CF set if wait time satisfied
clear if driver must perform wait
note 1) Used by NETBIOS, TOPS Network, Tom Wagner's CTASK multitasker.
2) Generic type codes are allocated as follows:
00h-7Fh non-reentrant devices; OS must arbitrate access
serially reusable devices
80h-0BFh reentrant devices; ES:BX points to a unique control block
0C0h-0FFh wait-only calls, no complementary POST int 15/fn 91h call
3) Invoked by the BIOS disk, printer, network, and keyboard handlers prior
to performing a programmed wait for I/O completion.
4) A multitasking program manager would be expected to capture int 15h/
fn 90h so that it can dispatch other tasks while I/O is in progress.
5) The default BIOS routine for this function simply returns with the CF
clear and AH=00h.
Function 91h Interrupt Completed (AT, XT/286, PS/2 50+)
entry AH 91h
AL type code (see AH=90h above)
00h-7Fh serially reusable devices
80h-0BFh reentrant devices
ES:BX pointer to request block for type codes 80h through 0BFh
return AH 00h
note 1) Used by NETBIOS and TOPS network, Tom Wagner's CTASK multitasker.
2) Invoked by the BIOS disk network, and keyboard handlers to signal that
I/O is complete and/or the device is ready.
3) Predefined device types that may use Device POST are:
00H disk (may timeout)
01H floppy disk (may timeout)
02H keyboard (no timeout)
03H PS/2 pointing device (may timeout)
80H network (no timeout)
4) The BIOS printer routine does not invoke this function because printer
output is not interrupt driven.
5) A multitasking program manager would be expected to capture int 15h/
fn 91h so that it can be notified when I/O is completed and awaken the
requesting task.
6) The default BIOS routine for this function simply returns with the CF
flag clear and AH=00h.
Function 0C0h Get System Configuration (XT after 1/10/86, PC Convertible,
XT/286, AT, PS/2)
entry AH 0C0h
return CF set if BIOS doesn't support call
ES:BX pointer to ROM system descriptor table
bytes 00h-01h number of bytes in the following table (norm. 16 bytes)
02h system ID byte; see Chapter 2 for interpretation
03h secondary ID distingushes between AT and XT/286, etc.
04h BIOS revision level, 0 for 1st release, 1 for 2nd, etc.
05h feature information byte
bits 0 reserved
1 Micro Channel bus (instead of ISA or EISA)
2 extended BIOS area allocated at 640k
3 wait for external event supported (int 15fn41)
used on Convertible; reserved on PS/2 systems
4 kbd intrcpt:int 15h, fn 04h called upon int 09h
5 realtime clock installed
6 second 8259 installed (cascaded IRQ2)
7 DMA channel 3 - used by hard disk BIOS
06h unknown (set to 0) (reserved by IBM)
07h unknown (set to 0) (reserved by IBM)
08h unknown (set to 0)
09h unknown (set to 0) (Award BIOS copyright here)
note 1) Int 15h is also used for the Multitask Hook on PS/2 machines. No
register settings available yet.
2) The 1/10/86 XT BIOS returns an incorrect value for the feature byte.
3) Novell documents some versions of Netware prior to 2.2 as having
problems on PS/2 machines due to a bug which did not return from the
interrupt correctly.
4) Some AMI BIOSes do not support this function. (early Dell machines)
Function 0C1h Return Extended BIOS Data Area Segment Address (PS/2)
entry AH 0C1h
return CF set on error
ES segment of XBIOS data area
note 1) The XBIOS Data Area is allocated at the high end of conventional memory
during the POST (Power-On-Self-Test) sequence.
2) The word at 0040:0013h (memory size) is updated to reflect the reduced
amount of memory available for DOS and application programs.
3) The 1st byte in the XBIOS Data Area is initialized to its length in K.
4) A program can determine whether the XBIOS Data Area exists by using
int 15h/fn 0C0h.
Function 0C2h Pointing Device BIOS Interface (DesQview 2.x) (PS/2)
entry AH 0C2h
AL 00h Enable/Disable Pointing Device
BH 00h disable
01h enable
01h Reset Pointing Device
Resets the system's mouse or other pointing device,
sets the sample rate, resolution, and other
characteristics to their default values.
return BH device ID (0=first)
note 1) After a reset operation, the state of the
pointing device is as follows:
disabled;
sample rate at 100 reports per second;
resolution at 4 counts per millimeter;
scaling at 1 to 1.
2) The data package size is unchanged by this fn.
3) Apps can use the fn 0C2h subfunctions to
initialize the pointing device to other parms,
then enable the device with fn 00h.
4) BL is altered on return.
02h Set Sampling Rate
BH 00h 10/second
01h 20/second
02h 40/second
03h 60/second
04h 80/second
05h 100/second (default)
06h 200/second
03h Set Pointing Device Resolution
BH 00h one count per mm
01h two counts per mm
02h four counts per mm (default)
03h eight counts per mm
04h Get Pointing Device Type
return BH ID code for the mouse or other pointing
device
05h Initialize Pointing Device Interface
Sets the data package size for the system's mouse or
other pointing device, and initializes the resolution,
sampling rate, and scaling to their default values.
BH data package size (1 - 8 bytes)
note After this operation, the state of the pointing
device is as follows:
a) disabled;
b) sample rate at 100 reports per second;
c) resolution at 4 counts per millimeter;
d) scaling set at 1 to 1.
06h Get Status or Set Scaling Factor
Returns the current status of the system's mouse or
other pointing device or sets the device's scaling
factor.
BH 00h return device status
return BL status byte
bits 0 set if right button pressed
1 reserved
2 set if left button pressed
3 reserved
4 0 1:1 scaling
1 2:1 scaling
5 0 device disabled
1 device enabled
6 0 stream mode
1 remote mode
7 reserved
CL resolution
00h 1 count per millimeter
01h 2 counts per millimeter
02h 4 counts per millimeter
03h 8 counts per millimeter
DL sample rate (hex count)
0Ah 10 reports per second
14h 20 reports per second
28h 40 reports per second
3Ch 60 reports per second
50h 80 reports per second
64h 100 reports per second
0C8h 200 reports per second
01h set scaling to 1:1
02h set scaling to 2:1
07h Set Pointing Device Handler Address
Notifies BIOS pointing device driver of the address
for a routine to be called each time pointing device
data is available.
ES:BX address of user device handler
return AL 00h
return CF set on error
AH status
00h successful
01h invalid function
02h invalid input
03h interface error
04h need to resend
05h no device handler installed
note 1) The values in BH for those functions that take it as input are stored
in different locations for each subfunction.
2) The user's handler for pointing device data is entered via a far call
with four parameters on the stack:
SS:SP+0Ah status
SS:SP+08h x coordinate
SS:SP+06h y coordinate
SS:SP+04h z coordinate (always 0)
The handler must exit via a far return without removing the parameters
from the stack.
3) The status parameter word passed to the user's handler is interpreted
as follows:
bits 0 left button pressed
1 right button pressed
2-3 reserved
4 sign of x data is negative
5 sign of y data is negative
6 x data has overflowed
7 y data has overflowed
8-0Fh reserved
Function 0C3h Enable/Disable Watchdog Timeout (PS/2 50+)
entry AH 0C3h
AL 00h disable watchdog
01h enable watchdog
BX timer counter
return CF set on error
note 1) The watchdog timer generates an NMI.
2) This would be subject to protection with a real OS so temporary masters
would not be able to seize the bus forever.
Function 0C4h Programmable Option Select (PS/2 50+)
entry AH 0C4h
AL 00h return base POS register address
01h enable slot
BL slot number
02h enable adapter
return CF set on error
DX base POS register address (if function 00h)
note 1) Fn 00h returns the base Programmable Option Select register address,
enables a slot for setup, or enables an adapter.
2) Valid on machines with Micro Channel Architecture (MCA) bus only.
3) After a slot is enabled with fn 01h, specific information can be
obtained for the adapter in that slot by performing port input
operations:
Port Function
100h MCA ID (low byte)
101h MCA ID (high byte)
102h Option Select Byte 1
bit 0 0 if disabled
1 if enabled
103h Option Select Byte 2
104h Option Select Byte 3
105h Option Select Byte 4
bits 6-7 are channel check indicators
106h Subaddress Extension (low byte)
107h Subaddress Extension (high byte)
Function 0C5h Used by PS/2 Model 50+ and Olivetti MCA machines
Used by Desqview 2.2
Used by Lotus 123 Release 2.2
Used by Microsoft Word 5.0
note Functions unknown. Reported by InfoWorld Nov 13 1989's Micro Channel
386 test as a conflict between the above software packages. InfoWorld
said that Quarterdeck (Desqview) was working on a fix for their
product. No other information.
Function 0DEh DesQview Services (DesQview)
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(0:0058h) Access the keyboard. Scancodes are found in Appendix 1. ASCII
codes are found in Appendix 2.
IBM's original keyboard layout is referred to as the 84-key
or "old style". It has the function keys on the left and an
embedded cursor/numeric keypad on the right. The 101-key "new
style" or "enhanced" keyboard (such as used on the PS/2s) adds
several keys. The early BIOS will not detect the new scancodes
and the new BIOS for some reason added new function calls for
this purpose instead of enhancing the old ones. This causes
some hassle when writing programs which need to support both
keyboards fully. Most programs limit themselves to the 84-key
functions in the interest of backward compatibility.
The SWITCHES CONFIG.SYS command forces DOS 4.0 to use the
standard int 16h requests for keyboard I/O rather than the
extended int 16h requests.
The DOS KEYB command does not hook into the BIOS. It is a total
replacement for the BIOS int9 driver. The only good thing about
this is that you can use 101-key keyboards on old ATs without
support for enhanced keyboards. KEYB is very peculiar in its
handling of the keyboard, causing some programs to break. It
also tends to disable interrupts for a long time while process-
ing each scan code.
There are machines such as the Toshiba 5200 which have 84-key
layouts but "simulate" being 101-key, at least as far as int 16
goes. (always good for confusing your software...)
Function 00h Get Keyboard Input - read the next character in keyboard buffer,
if no key ready, wait for one.
entry AH 00h
return AH scan code
AL ASCII character
note 1) Removes keystroke from buffer (destructive read).
2) Does not work with the extra keys on the 101-key "enhanced" keyboard.
Function 01h Check Keystroke Buffer - Do Not Clear
entry AH 01h
return ZF 0 (clear) if character in buffer
1 (set) if no character in buffer
AH scan code of character (if ZF=0)
AL ASCII character if applicable
note 1) Keystroke is not removed from buffer. The same character and scan code
will be returned by the next call to Int 16h/fn 00h.
2) This call flushes the 101-key codes from the buffer if they precede
an 84-key code.
Function 02h Shift Status - fetch bit flags indicating shift status
entry AH 02h
return AL status byte (same as [0040:0017])
bits 7 Insert on
6 CapsLock on
5 NumLock on
4 ScrollLock on
3 Alt key down
2 Control key down
1 Left shift (left caps-shift key) down
0 Right shift (right caps-shift key) down
note The Keyboard Flags Byte is stored in the BIOS Data Area at 0000:0417h.
Function 03h Keyboard - Set Repeat Rate (PCjr, AT, XT/286, PS/2)
entry AH 03h
AL 00h reset typematic defaults (PCjr)
01h increase initial delay (PCjr)
02h decrease repeat rate by 1/2 (PCjr)
03h increase both delays by 1/2 (PCjr)
04h turn off typematic (PCjr)
05h set typematic rate (AT, PS/2)
BH 00h-03h for delays of 250ms, 500ms, 750ms, or 1 second
0,0 250ms
0,1 500ms
1,0 750ms
1,1 1 second
BL 00h-1Fh for typematic rates of 30cps down to 2cps
00000 30 01011 10.9 10101 4.5
00001 26.7 01100 10 10110 4.3
00010 24 01101 9.2 10111 4
00011 21.8 01110 8.6 11000 3.7
00100 20 01111 8 11001 3.3
00101 18.5 10000 7.5 11010 3
00110 17.1 10001 6.7 11011 2.7
00111 16 10010 6 11100 2.5
01000 15 10011 5.5 11101 2.3
01001 13.3 10011 5.5 11110 2.1
01010 12 10100 5 11111 2
return nothing
note 1) Subfunction 05h is available on ATs with ROM BIOS dated 11/15/85 and
later, the XT/286, and the PS/2.
2) Subfunction 0 (Return to Default Keyboard State) restores the keyboard
to its original state. The original state at power-on is typematic on,
normal initial delay and normal typematic rate.
3) Subfunction 1 (Increase Initial Delay) increases the delay between the
first character typed and the burst of typematic characters.
4) For Subfunctions 0 through 4, each time the typematic rate is changed,
all previous states are removed.
5) Some clone keyboards (Northgate Omnikey and Focus) have much higher
repeat rates for the same bit values.
Function 04h Keyboard Click Toggle (PCjr and Convertible)
entry AH 04h
AL 00h for click off
01h for click on
return nothing
Function 05h Load Keyboard Buffer (AT or PS/2 with enhanced kbd)
entry AH 05h
CH scan code
CL ASCII character
return CF set on error
AL 00h success
01h if buffer full
note Places a character and scan code at the end of the keyboard type-ahead
buffer.
Function 06h Keyboard Buffer Write (Fansi-Console to 2.00)
entry AH 06h
BX extended key value to place in typeahead buffer
return unknown
note This call may be dropped since it now duplicates function 05h.
Function 07h Change Shift Key Status (Fansi-Console to 2.00)
entry AH 07h
AL shift key status value
return unknown
note Status byte is same as function 02h.
Function 10h Get Enhanced Keystroke And Read (F11, F12 Enhanced Keyb'd)
(XT/286, PS/2, AT with "Enhanced" keyboard)
entry AH 10h
return AH scan code
AL ASCII character if applicable
note 1) Reads a character and scan code from the keyboard type-ahead buffer.
2) Use this function for the enhanced keyboard instead of int 16h fn 00h.
It allows applications to obtain the scan codes for the additional F11,
F12, and cursor control keys.
3) This is the enhanced version of function 00h.
Function 11h Check Enhanced Keystroke (F11-F12 on enhanced keyboard)
(XT/286, PS/2, AT with "Enhanced" keyboard)
entry AH 11h
return ZF 0 (clear) if key pressed
AH scan code
AL ASCII character if applicable
1 if buffer is empty
note 1) Keystroke is not removed from buffer. The same char and scan code will
be returned by the next call to Int 16h/fn 10h.
2) Use this function for the enhanced keyboard instead of int 16h/fn 00h.
It allows applications to test for the additional F11, F12, and cursor
control keys.
Function 12h Extended Get Shift Status (F11, F12 Enhanced keyboard)
entry AH 12h
return AX status word
AL bit 0 right Shift key depressed
1 left Shift key depressed
2 Control key depressed
3 Alt key depressed
4 ScrollLock state active
5 NumLock state active
6 CapsLock state active
7 insert state is active
AH bit 0 left Control key pressed
1 left Alt key depressed
2 right Control key pressed
3 right Alt key depressed
4 Scroll Lock key depressed
5 NumLock key depressed
6 CapsLock key depressed
7 SysReq key depressed
note Use this function for the enhanced keyboard instead of int 16h/fn 02h.
Function 70h, 71h, 72h Internal Functions (SEAware's FAKEY.COM)
note FAKEY.COM is a TSR keyboard utility distributed to registered users
of SEAware products.
Function 75h Set Tick Count for Scanning (pcAnywhere 2.00)
entry AH 75h
AL tick count
return none
note 1) Sets count of 55ms timer ticks between checks for new screen changes.
2) pcAnywhere is a program that allows operation of a remote machine
over a serial link.
Function 76h Set Error Checking Mode (pcAnywhere 2.00)
entry AH 76h
AL error checking type
00h none
01h fast
02h slow
return none
Function 77h reserved (pcAnywhere 2.00)
pcAnywhere API - reserved
Function 78h Log Off (pcAnywhere 2.00)
entry AL 00h wait for another call
01h exit but remain TSR
02h automatic mode - watches DTR
0FFh leave in current operating mode (pcAnywhere 2.1)
return none
Function 79h Installation Check (pcAnywhere 2.00)
entry AH 79h
AL 00h installation check
return AX 0FFFFh resident and active
0FFFEh resident but not active
0FFFDh resident TSR
0FFFCh automatic mode
any other value - not resident
Function 7Ah Cancel pcAnywhere Session (pcAnywhere 2.00)
entry AH 7Ah
return none
note Leaves pcAnywhere resident but unable to answer another call.
Function 7Bh Enable/Disable Operation (pcAnywhere 2.00)
entry AH 7Bh
AL state
00h disabled
01h enabled
return none
note Remote screen is automatically refreshed when session is enabled.
Function 7Ch Get Port Configuration (pcAnywhere 2.00)
entry AH 7Ch
return AH port number in binary (0-15)
AL baud rate
00h 50
01h 75
02h 110
03h 134.5
04h 150
05h 300
06h 600
07h 1200
08h 1800
09h 2000
0Ah 2400
0Bh 4800
0Ch 7200
0Dh 9600
0Fh 19,200
Function 7Dh Get/Set Terminal Parameters (pcAnywhere 2.00)
entry AH 7Dh
AL 00h set parameters
01h get parameters
02h get configuration header and terminal parameters
CX:DS address of Terminal Parameter Block
return AL 00h nothing
01h current Terminal Parameter Block in CX:DS
02h configuration header and Terminal Parameter Block
in CX:DS
note Terminal Parameter Block format: (1152 bytes) (decimal)
384 bytes CRT Control Information
bytes function
1-8 cursor up
9-16 cursor down
17-24 cursor left
25-32 cursor right
33-40 cursor home
41-48 clear screen
49-56 clear to end of line
57-64 clear to end of page
65-72 insert line
73-80 delete line
81-88 insert character
89-96 delete character
97-104 cursor position lead in
105-112 between row and column
113-120 after cursor position
121-128 CRT initialization
256 bytes Character Translation Table
translates ASCII characters from host. Normally changes IBM
graphics characters to other displayable symbols
512 bytes keyboard sequences
641-644 cursor up
645-648 cursor down
649-652 cursor left
653-656 cursor right
657-660 home
661-664 end
665-668 PgUp
669-672 PgDn
673-676 insert
677-680 delete
681-684 control-home
685-688 control-end
689-692 control-PgUp
693-696 control-PgDn
697-700 escape
701-740 F1...F10
741-780 sF1...sF10
781-820 ^F1...^F10
821-860 aF1...aF10
861-964 alt A-Z
965-1004 alt 0-9
1005-1008 alt =
1009-1012 alt -
1013-1016 print screen
1017-1020 ctrl-left arrow
1021-1024 ctrl-right arrow
1025-1120 reserved
1121-1124 begin conv. mode
1125-1128 remote printing off
1129-1132 remote printing on
1133-1136 backspace
1137-1140 refresh screen
1141-1144 send next code
1145-1148 display top 24 lines
1149-1152 display bottom 24 lines
Function 7Eh Serial I/O Through pcAnywhere Port (pcAnywhere 2.00)
entry AH 7Eh
AL I/O function
01h get port input status
02h get port input character
03h output character
04h hang up phone
CX ASCII character to output (fn 03h)
return (if AL=01h)
AX 00h no character ready
01h character is available
(if AL=02h)
AL ASCII code received
Function 7Fh Set Keyboard/Screen Mode (pcAnywhere 2.00)
entry AH 7Fh
AL parameters
00h enable remote keyboard only |
01h enable host keyboard only | keyboard group
02h enable both keyboards |
08h display top 24 lines | screen group
09h display bottom 24 lines |
10h Hayes modem |
11h other modems | modem group
12h direct connect |
Function 0EDh Borland Turbo Lightning API (partial)
entry AH 0EDh
BH 0EDh
BL function
00h installation check
02h pointer to Lightning internal data structure lobyte
03h pointer to Lightning internal data structure hibyte
04h load auxiliary dictionary
06h autoproof mode
0Fh get number of substitutions (segment)
DS:DI pointer to string to be processed
return AX error code (unknown)
note I've made several attempts to get a copy of the Turbo Lightning API,
which was originally supposed to be available for developers in 1985.
In 1988 Borland sent me a letter saying they were still working on it.
In late 1989 the Borland rep on BIX told me basically that there were
no plans for releasing the API any more. The information here was
dredged from Chris Dunford's LSPELL.PAS interface into Lighting.
Function 0F0h Set CPU speed (Compaq 386)
entry AH 0F0h set speed
AL speed
00h equivalent to 6 mHz 80286 (COMMON)
01h equivalent to 8 mHz 80286 (FAST)
02h full 16 mHz (HIGH)
03h toggles between 8 mHz-equivalent and speed set by
system board switch (AUTO or HIGH)
04h-07h unknown
08h full 16 mHz except 8 mHz-equivalent during floppy disk
access
09h specify speed directly
CX speed value, 1 (slowest) to 50 (full), 3 ~=8088
return none?
note 1) Used by Compaq DOS MODE command.
Function 0F1h Read Current CPU Speed (Compaq 386)
entry AH 0F1h
return AL speed code (see function 0F0h above)
if AL=09h, CX=speed code
Function 0F2h Determine Attached Keyboard Type (Compaq 386)
entry AH 0F2h
return AL type
00h if 11-bit AT keyboard is in use
01h if 9-bit PC keyboard is in use
Function 0FFh PC-Tools API
entry AH 0FFh
other parameters unknown
note PC-Tools is a Swiss-army-knife software package with an editor, DOS
shell, cache, disk optimizer, and several other functions from Central
Point Software.
Function 0FFh 2-The-Max VGA-16 Board
entry AH 0FFh query zoom interrupt
return AL zoom interrupt number
AL+1 old BIOS keyboard handler interrupt number
BX hot key
Function 0FFh Programmer Interface to Carbon Copy Plus (5.0)
entry AH 0FFh
AL 00h check connection between CC and CCHELP
return BL 00h Carbon Copy not connected to CCHELP
01h Carbon Copy is connected to CCHELP
entry AL 01h disconnects and resets the line if the Host or CC
side is connected to CCHELP
entry AL 02h return a pointer to the last phone number dialed by CC
return ES:DI dword pointer to ASCIIZ phone number string
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쿔nterrupt 17h Printer 3**10 �
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(0:005Ch) access the parallel printer(s)
AH is changed. All other registers left alone.
Printer ports vary widely in compatibility, since the original
IBM MDA's parallel port did not match its own spec. Many
parallel ports do not use IRQ7 at all.
The parallel port on a monochrome adapter is at 3BCh. The port
on a parallel printer adapter is at 378h or 278h. At boot time,
the BIOS looks at them in the order 3BCh, 378h, 278h, and
assigns the first port it finds to LPT1, the second to LPT2,
etc. If you have a monochrome adapter, LPT1 is probably 3BCh;
otherwise, it is probably 378h.
Function 00h Print Character/send AL to printer DX (0, 1, or 2)
entry AH 00h
AL ASCII character code
DX printer to be used
00h PRN or LPT1
01h LPT2
02h LPT3
return AH status byte
bits 0 time out
1 unused
2 unused
3 I/O error
4 printer selected
5 out of paper
6 acknowledge
7 not busy
Function 01h Initialize Printer - set init line low, send 0Ch to printer DX
entry AH 01h
DX printer port to be initialized (0,1,2)
return status as below
Function 02h Printer Status - read status of printer DX into AH
entry AH 02h
DX printer port to be used (0,1,2)
return AH status byte
bits 7 0 busy/paused: the printer cannot immediately
take more data because it is in the middle of
accepting a character, printing a line, is
offline, or it is in error status.
1 ready
6 ACKnowledge line toggled: reflects the state of the ACK
line on the printer port at the moment the status was read.
ACK is a strobe: it goes low for a very short time (12
microseconds on an Epson) when the printer is ready for
another character. As far as printer status is concerned,
this is useless; it's only useful for something like an
interrupt-driven interface. Most of the time, you'll see
ACK high (bit 6 on), but occasionally, if you check status
just after sending a character, you might see it low.
ACK is low when the printer is powered off.
5 out-of-paper line toggled
4 printer selected: printer is selected/ready/online. There
is usually a button on the printer to control this.
3 I/O error: offline, out of paper or other error condition
such as out of ribbon.
2 unused
1 unused
0 timeout error: printer failed to send ACK and drop busy
after being sent a character.
note 1) You can expect to see these states in a properly functioning printer:
Normal Offline Power off
====== ======= =========
not busy/paused busy/paused busy/paused
not out of paper not out of paper not out of paper
selected/online not selected/online not selected/online
not I/O error I/O error (usually) I/O error
not timeout error not timeout error not timeout error
2) Not all printers return the status codes properly. That's OK, not all
clone BIOS do it right either. If your program depends on the return
codes, you might want to make the code easily patched or configured
for nonstandard hardware.
Function 03h Versa-Spool print spooler
entry AH 03h Versa-Spool
AL 00h Return Signature
01h Toggle Pause
02h Clear Buffer
03h Request Pause Condition
04h Request Free Buffer Space
05h Request Total Buffer Size
06h Redirect Output to LPT1
07h Redirect Output to LPT2
08h Redirect Output to LPT3
09h Request Output Device
0Ah Request Output Speed
0Bh Request Device Spooled Status
return (AH=00h) AX 1234h if Versa-Spool is installed
undefined if not installed
(AH=01h) AX 0001h if paused
0000h if resumed
(AH=02h) AX 0302h not cleared
0000h cleared
(AH=03h) AX 0001h if paused
0000h if resumed
(AH=04h) AX remaining buffer space (in Kbytes)
(AH=05h) AX total buffer space (in Kbytes)
(AH=06h) AX nothing
(AH=07h) AX nothing
(AH=08h) AX nothing
(AH=09h) AX printer output (0..2)
(AH=0Ah) AX output speed in CPS
(AH=0Bh) AX 0001h is spooled
0000h otherwise
Function 0C0h PC Magazine PCSPOOL - get printer status
entry AH 0C0h
DX printer port to be used (0,1,2)
return ES:BX address of printer control block
note PC Magazine, January 15, 1991. (Vol 10, Number 1)
Function 0C1h PC Magazine PCSPOOL - add pause to spool queue
entry AH 0C1h
DX printer port to be used (0,1,2)
DS:SI pointer to ASCIIZ string to display
return AH printer status
Function 0C2h PC Magazine PCSPOOL - flush queue record
entry AH 0C2h
DX printer port to be used (0,1,2)
return AH printer status
Function 0C3h PC Magazine PCSPOOL - cancel printer queue
entry AH 0C3h
DX printer port to be used (0,1,2)
return AH printer status
Function 0C4h PC Magazine PCSPOOL - determine of spooler is active
entry AH 0C4h
return DI 0B0BFh if PCSPOOL is loaded
SI segment of the PSP of the active PCSPOOL
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 18h ROM BASIC 3**11 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0060h) Execute ROM BASIC at address 0F600h:0000h
entry no parameters used
return jumps into ROM BASIC on IBM systems
note 1) Often reboots a compatible.
2) Used by Turbo C 1.5. 2.0 and later do not use it.
3) On IBM systems, this interrupt is called if disk boot failure occurs.
4) Video interrupt on DEC Rainbow.
5) Digital Research's ROM-based implementation of DR-DOS uses int 18h as
the initial entry vector into the operating system code. Note that
some clone BIOSes may not properly implement int 18h in the ROM and
use of DR-DOS ROMs may not always work.
6) Maxon 286/HD laptop: called by BIOS power management routines to
communicate with applications.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 19h Bootstrap Loader / Extended Memory VDISK ID 3**12 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0064h)
entry no parameters used
return none
note 1) Reads track 0, sector 1 into address 0000h:7C00h, then transfers
control to that address. If no diskette drive available, looks at
absolute address C:800 for a valid hard disk or other ROM. If none,
transfers to ROM-BASIC via int 18h or displays loader error message.
2) Causes reboot of disk system if invoked while running. (no memory test
performed).
3) If location 0000:0472h does not contain the value 1234h, a memory test
(POST) will be performed before reading the boot sector.
4) VDISK from DOS 3.0+ traps this vector to determine when the CPU has
shifted from protected mode to real mode. A detailed discussion can
be found by Ray Duncan in PC Magazine, May 30, 1989.
5) Reportedly, some versions of DOS 2.x and all versions of DOS 3.x+
intercept int 19h in order to restore some interrupt vectors DOS takes
over, in order to put the machine back to a cleaner state for the
reboot, since the POST will not be run on the int 19h. These vectors
are reported to be: 02h, 08h, 09h, 0Ah, 0Bh, 0Ch, 0Dh, 0Eh, 70h, 72h,
73h, 74h, 75h, 76h, and 77h. After restoring these, it restores the
original int 19h vector and calls int 19h.
6) The system checks for installed ROMs by searching memory from 0C000h to
the beginning of the BIOS, in 2k chunks. ROM memory is identified if it
starts with the word 0AA55h. It is followed a one byte field length of
the ROM (divided by 512). If ROM is found, the BIOS will call the ROM
at an offset of 3 from the beginning. This feature was not supported in
the earliest PC machines. The last task turns control over to the
bootstrap loader (assuming the floppy controller is operational).
7) 8255 port 60h bit 0 = 1 if booting from diskette.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 1Ah Time of Day 3**13 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0068h) 1) Accesses the PC internal clock.
2) This interrupt is not supported on some machines, such as
the HP150 PC.
3) Some "turbo" BIOSes run the clock slower than normal in order
to throw off benchmark software, which usually uses int 1Ah
for timekeeping.
4) Counts occur at the rate of 1193180/65536 counts/sec (about
18.2 per second).
Function 00h Read System Timer Tick Counter (except PC)
entry AH 00h
return AL 00h if clock was read or written (via AH=0,1) within the
current 24-hour period.
<>0 midnight was passed since last read
CX:DX 32-bit tick count (high 16 bits in CX)
note 1) The returned value is the cumulative number of clock ticks since
midnight. There are 18.2 clock ticks per second, or one every 54.92ms.
When the counter reaches 1,573,040, it is cleared to zero, and the
rollover flag is set.
2) The rollover flag is cleared by this function call, so the flag will
only be returned nonzero once per day.
3) Int 1Ah/fn 01h can be used to set the counter to an arbitrary 32 bit
value.
4) This function does not return seconds/100 in DL. The best you can do
is set it to zero (or any value <=99). This means that your DOS clock
could be up to 1 second off from the BIOS clock, however the effect is
not cumulative.
Function 01h Set Clock Tick Counter Value (except PC)
entry AH 01h
CX:DX 32-bit high word/low word count of timer ticks
return none
note 1) The clock ticks are incremented by timer interrupt at 18.2065 times
per second or 54.9254 milliseconds/count. Therefore:
counts per second 18 (12h)
counts per minute 1092 (444h)
counts per hour 65543 (10011h)
counts per day 1573040 (1800B0h)
2) The counter is zeroed when system is rebooted.
3) Stores a 32-bit value in the clock tick counter.
4) The rollover flag is cleared by this call.
Function 02h Read Real Time Clock Time (AT and after)
entry AH 02h
return CH hours in BCD
CL minutes in BCD
DH seconds in BCD
DL 00h standard time
01h daylight savings time
CF 0 if clock running
1 if clock not operating
note 1) Reads the current time from the CMOS time/date chip.
2) Also for Leading Edge Model M.
3) According to Phoenix this call will fail if the BIOS is "updating" its
clock value. You should check the carry flag and retry if it is set
following the call.
Function 03h Set Real Time Clock Time (AT and after)
entry AH 03h
CH hours in BCD
CL minutes in BCD
DH seconds in BCD
DL 0 (clear) if standard time
1 (set) if daylight savings time option
return none
note 1) Sets the time in the CMOS time/date chip.
2) Also for Leading Edge Model M.
Function 04h Read Real Time Clock Date (AT and after)
entry AH 04h
return CH century in BCD (19 or 20)
CL year in BCD
DH month in BCD
DL day in BCD
CF 0 (clear) if clock is running
1 (set) if clock is not operating
note 1) Reads the current date from the CMOS time/date chip.
2) Also for Leading Edge Model M.
Function 05h Set Real Time Clock Date (AT and after)
entry AH 05h
CH century in BCD (19 or 20)
CL year in BCD
DH month in BCD
DL day in BCD
return none
note 1) Sets the date in the CMOS time/date chip.
2) Also for Leading Edge Model M.
Function 06h Set Real Time Clock Alarm (AT and after)
entry AH 06h
CH hours in BCD
CL minutes in BCD
DH seconds in BCD
return CF set if alarm already set or clock inoperable
note 1) Sets alarm in the CMOS date/time chip. Int 4Ah occurs at specified
alarm time every 24hrs until reset with Int 1Ah/fn 07h.
2) A side effect of this function is that the clock chip's interrupt
level (IRQ8) is enabled.
3) Only one alarm may be active at any given time.
4) The program using this function must place the address of its interrupt
handler for the alarm in the vector for Int 4Ah.
Function 07h Reset Real Time Clock Alarm (AT and after)
entry AH 07h
return none
note 1) Cancels any pending alarm request on the CMOS date/time chip.
2) This function does not disable the clock chip's interrupt level (IRQ8).
Function 08h Set Real Time Clock Activated Power On Mode (Convertible)
entry AH 08h
CH hours in BCD
CL minutes in BCD
DH seconds in BCD
Function 09h Read Real Time Clock Alarm Time and Status
(Convertible and PS/2 Model 30)
entry AH 09h
return CH hours in BCD
CL minutes in BCD
DH seconds in BCD
DL alarm status:
00h if alarm not enabled
01h if alarm enabled but will not power up system
02h if alarm will power up system
Function 0Ah Read System-Timer Day Counter (PS/2)
entry AH 0Ah
return CF set on error
CX count of days since Jan 1,1980
note Returns the contents of the system's day counter.
Function 0Bh Set System-Timer Day Counter (PS/2)
entry AH 0Bh
CX count of days since Jan 1,1980
return CF set on error
note Stores an arbitrary value in the system's day counter.
Function 80h Set Up Sound Multiplexor (PCjr) (Tandy 1000?)
entry AH 80h
AL sound source
00h source is 8253 timer chip, channel 2
01h source is cassette input
02h source is I/O channel "audio in" line
03h source is TI sound generator chip
return none
note Sets up the source for tones that will appear on the PCjr's Audio Out
bus line or RF modulator.
Function 1Ah Read Time and Date (AT&T 6300)
entry AH 0FEh
return BX days count (1=Jan 1, 1984)
CH hours
CL minutes
DH seconds
DL hundredths
note Day count in BX is unique to AT&T/Olivetti computers.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 1Bh Control-Break 3**14 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:006Ch) This interrupt is called when the keyboard handler of the IBM
machines detects Ctrl and Break pressed at the same time. DOS
normally point this interrupt at its own Ctrl-Break handler.
note 1) If the break occurred while processing an interrupt, one or more
end of interrupt commands must be send to the 8259 Programmable
Interrupt Controller.
2) All I/O devices should be reset in case an operation was underway at
the time.
3) It is normally pointed to an IRET during system initialization so that
it does nothing, but some programs change it to return a Ctrl-C scan
code and thus invoke int 23h.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 1Ch Timer Tick 3**15 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0070h)
note 1) Taken 18.2065 times per second by the int 08h interrupt.
2) Normally vectors to dummy IRET unless PRINT.COM has been installed.
3) If an application moves the interrupt pointer, it is the responsibility
of that application to save and restore all registers that may be
modified.
4) returns values at absolute address 40:6x (BIOS Data Area); number of
ticks since midnight
40:6C word timer counter high word
40:6E word timer counter low word
5) Ventura Publisher 2.0 grabs this interrupt and does not pass subsequent
vector reassignments along. This causes problems with some TSRs and
network software.
6) When installing a user interrupt for int 1Ch, the external interrupts
must be disabled before the vector is altered. If a timer interrupt
occurs between the setting of the offset and segment, an incorrect
address will result.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 1Dh Vector of Video Initialization Parameters 3**16 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0074h) This doubleword address points to 3 sets of 16-bytes containing
data to initialize for video modes for video modes 0 & 1 (40
column), 2 & 3 (80 column), and 4, 5 & 6 (graphics) on the
Motorola 6845 CRT controller chip.
6845 registers:
R0 horizontal total (horizontal sync in characters)
R1 horizontal displayed (characters per line)
R2 horizontal sync position (move display left or right)
R3 sync width (vertical and horizontal pulse: 4-bits each)
R4 vertical total (total character lines)
R5 vertical adjust (adjust for 50 or 60 Hz refresh)
R6 vertical displayed (lines of chars displayed)
R7 vertical sync position (lines shifted up or down)
R8 interlace (bits 4 and 5) and skew (bits 6 and 7)
R9 max scan line addr (scan lines per character row)
R10 cursor start (starting scan line of cursor)
R11 cursor stop (ending scan line of cursor)
R12 video memory start address high byte (6 bits)
R13 video memory start address low byte (8 bits)
R14 cursor address high byte (6 bits)
R15 cursor address low byte (8 bits)
6845 Video Init Tables:
table for modes 0 and 1 \
table for modes 2 and 3 \ each table is 16 bytes long and
table for modes 4,5, and 6 / contains values for 6845 registers
table for mode 7 /
4 words size of video RAM for modes 0/1, 2/3, 4/5, and 6/7
8 bytes number of columns in each mode
8 bytes video controller mode byte for each mode
note 1) There are 4 separate tables, and all 4 must be initialized if all
video modes will be used.
2) The power-on initialization code of the computer points this vector
to the ROM BIOS video routines.
3) IBM recommends that if this table needs to be modified, it should be
copied into RAM and only the necessary changes made.
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쿔nterrupt 1Eh Vector of Diskette Controller Parameters 3**17 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0078h) Dword address points to data base table that is used by BIOS.
Default location is at 0F000:0EFC7h. 11-byte table format:
bytes:
00h 4-bit step rate, 4-bit head unload time
01h 7-bit head load time, 1-bit DMA flag
02h 54.9254 ms ticks - delay til motor off (36-38 typical)
03h sector size:
00h 128 bytes
01h 256 bytes
02h 512 bytes
03h 1024 bytes
04h last sector on track (8 or 9 typical)
05h inter-sector gap on read/write (42 typical)
06h data length for DMA transfers (0FFh typical)
07h gap length between sectors for format (80 typical)
08h sector fill byte for format (0F6h typical)
09h head settle time (in milliseconds) (15 to 25 typical)
DOS 1.0 0
DOS 1.10 0
DOS 2.10 15
DOS 3.1 1
0Ah motor start time (in 1/8 sec intervals) (2-4 typical)
DOS 2.10 2
note 1) This vector is pointed to the ROM BIOS diskette tables on system
initialization
2) IBM recommends that if this table needs to be modified, it should be
copied into RAM and only the necessary changes made.
3) Some versions of DOS 3.2 may contain a bug. DOS 3.2 assumes that the
dword at 0070:0F37 contains the address of the diskette parameter
block and changes values in that block. The location does contain a
copy of the value at 0:78 (int 1Eh, DISK_POINTER) if DOS is booted from
diskette, but when booted from the hard disk, the location contains
0:0. This leads to strange things, especially when running under a
debugger since DOS overwrites parts of the interrupt vectors for
interrupts 1 to 3. The solution to the problem is to either upgrade
to DOS 3.3 or to copy the disk parameter vector to 70:0F37 before
running or at the start of your program.
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쿔nterrupt 1Fh Ptr to Graphics Character Extensions (Graphics Set 2) 3**18 �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:007Ch) This is the pointer to data used by the ROM video routines to
display characters above ASCII 127 while in CGA medium and high
res graphics modes.
note 1) Doubleword address points to 1K table composed of 28 8-byte character
definition bit-patterns. First byte of each entry is top row, last byte
is bottom row.
2) The first 128 character patterns are located in system ROM.
3) This vector is set to 000:0 at system initialization.
4) Used by DOS' external GRAFTABL command.
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
C H A P T E R F O U R
DOS INTERRUPTS AND FUNCTION CALLS
note: The registered version of this chapter is twice this size.
DOS REGISTERS쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
DOS uses the following registers, pointers, and flags when it executes
interrupts and function calls:
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쿒ENERAL REGISTERS � register � definition �
� 쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� � AX � accumulator (16 bit) �
� � AH � accumulator high-order byte (8 bit) �
� � AL � accumulator low order byte (8 bit) �
� � BX � base (16 bit) �
� � BH � base high-order byte (8 bit) �
� � BL � base low-order byte (8 bit) �
� � CX � count (16 bit) �
� � CH � count high order byte (8 bit) �
� � CL � count low order byte (8 bit) �
� � DX � data (16 bit) �
� � DH � date high order byte (8 bit) �
� � DL � data low order byte (8 bit) �
쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
쿞EGMENT REGISTERS � register � definition �
� 쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� � CS � code segment (16 bit) �
� � DS � data segment (16 bit) �
� � SS � stack segment (16 bit) �
� � ES � extra segment (16 bit) �
쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
쿔NDEX REGISTERS � register � definition �
� 쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� � DI � destination index (16 bit) �
� � SI � stack index (16 bit) �
쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
쿞EGMENT REGISTERS � register � definition �
� 쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� � CS � code segment (16 bit) �
� � DS � data segment (16 bit) �
� � SS � stack segment (16 bit) �
� � ES � extra segment (16 bit) �
쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
쿔NDEX REGISTERS � register � definition �
� 쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� � DI � destination index (16 bit) �
� � SI � stack index (16 bit) �
쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
쿛OINTERS � register � definition �
� 쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� � SP � stack pointer (16 bit) �
� � BP � base pointer (16 bit) �
� � IP � instruction pointer (16 bit) �
쳐컴컴컴컴컴컴컴컴컴좔컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
쿑LAGS AF, CF, DF, IF, OF, PF, SF, TF, ZF �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
These registers, pointers, and flags are "lowest common denominator" 8088-8086
CPU oriented. DOS makes no attempt to use any of the special or enhanced
instructions availible on the later CPUs which will execute 8088 code, such as
the 80186, 80286, 80386, or NEV V20, V30, V40, or V50.
When DOS takes control after a function call, it switches to an internal
stack. Registers which are not used to return information (other than AX) are
preserved. The calling program's stack must be large enough to accomodate the
interrupt system - at least 128 bytes in addition to other interrupts.
DOS actually maintains three stacks -
stack 1: 384 bytes (in DOS 3.1)
for functions 00h and for 0Dh and up, and for ints 25h and 26h.
stack 2: 384 bytes (in DOS 3.1)
for function calls 01h through 0Ch.
stack 3: 48 bytes (in DOS 3.1)
for functions 0Dh and above. This stack is the initial stack used by
the int 21h handler before it decides which of the other two to use.
It is also used by function 59h (get extended error), and 01h to 0Ch if
they are called during an int 24h (critical error) handler. Functions
33h (get/set break flag), 50h (set process ID), 51h (get process ID)
and 62h (get PSP address) do not use any DOS stack under DOS 3.x
(under 2.x, 50h and 51h use stack number 2).
IBM and Microsoft made a change back in DOS 3.0 or 3.1 to reduce the size of
DOS. They reduced the space allocated for scratch areas when interrupts are
being processed. The default seems to vary with the DOS version and the
machine, but 8 stack frames seems to ring a bell. That means that if you get
more than 8 interrupts at the same time, clock, disk, printer spooler,
keyboard, com port, etc., the system will crash. It seems to happen usually on
a network. STACKS=16,256 means allow 16 interrupts to interrupt each other and
allow 256 bytes for each for scratch area. Eight is marginal.
DOS 3.2 does some different stack switching than previous versions. The
interrupts which are switched are 02h, 08h, 09h, 0Ah, 0Bh, 0Ch, 0Dh, 0Eh, 70h,
72h, 73h, 74h, 75h, 76h, and 77h. DOS 3.2 has a special check in the
initialization code for a PCjr and don't enable stack switching on that machine.
INTERRUPTS쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
Microsoft recommends that a program wishing to examine or set the contents of
any interrupt vector use the DOS function calls 35h and 25h provided for those
purposes and avoid referencing the interrupt vector locations directly.
DOS reserves interrupt numbers 20h to 3Fh for its own use. This means absolute
memory locations 80h to 0FFh are reserved by DOS. The defined interrupts are as
follows with all values in hexadecimal.
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 21h Function Call Request �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:0084h)
DOS provides a wide variety of function calls for character device I/O, file
management, memory management, date and time functions,execution of other
programs, and more. They are grouped as follows:
call description
00h program terminate
01h-0Ch character device I/O, CP/M compatibility format
0Dh-24h file management, CP/M compatibility format
25h-26h nondevice functions, CP/M compatibility format
27h-29h file management, CP/M compatibility format
2Ah-2Eh nondevice functions, CP/M compatibility format
2Fh-38h extended functions
39h-3Bh directory group
3Ch-46h extended file management
47h directory group
48h-4Bh extended memory management
54h-57h extended functions
5Eh-5Fh networking
60h-62h extended functions
63h-66h enhanced foreign language support
List of DOS services: * = undocumented
00h terminate program
01h get keyboard input
02h display character to STDIO
03h get character from STDAUX
04h output character to STDAUX
05h output character to STDPRN
06h direct console I/O - keyboard to screen
07h get char from std I/O without echo
08h get char from std I/O without echo, checks for ^C
09h display a string to STDOUT
0Ah buffered keyboard input
0Bh check STDIN status
0Ch clear keyboard buffer and invoke keyboard function
0Dh flush all disk buffers
0Eh select disk
0Fh open file with File Control Block
10h close file opened with File Control Block
11h search for first matching file entry
12h search for next matching file entry
13h delete file specified by File Control Block
14h sequential read from file specified by File Control Block
15h sequential write to file specified by File Control Block
16h find or create firectory entry for file
17h rename file specified by file control block
18h* unknown
19h return current disk drive
1Ah set disk transfer area (DTA)
1Bh get current disk drive FAT
1Ch get disk FAT for any drive
1Dh* unknown
1Eh* unknown
1Fh* read DOS disk block, default drive
20h* unknown
21h random read from file specified by FCB
22h random write to file specified by FCB
23h return number of records in file specified by FCB
24h set relative file record size field for file specified by FCB
25h set interrupt vector
26h create new Program Segment Prefix (PSP)
27h random file block read from file specified by FCB
28h random file block write to file specified by FCB
29h parse the command line for file name
2Ah get the system date
2Bh set the system date
2Ch get the system time
2Dh set the system time
2Eh set/clear disk write VERIFY
2Fh get the Disk Transfer Address (DTA)
30h get DOS version number
31h TSR, files opened remain open
32h* read DOS Disk Block
33h get or set Ctrl-Break
34h* INDOS Critical Section Flag
35h get segment and offset address for an interrupt
36h get free disk space
37h* get/set option marking character (SWITCHAR)
38h return country-dependent information
39h create subdirectory
3Ah remove subdirectory
3Bh change current directory
3Ch create and return file handle
3Dh open file and return file handle
3Eh close file referenced by file handle
3Fh read from file referenced by file handle
40h write to file referenced by file handle
41h delete file
42h move file pointer (move read-write pointer for file)
43h set/return file attributes
44h device IOCTL (I/O control) info
45h duplicate file handle
46h force a duplicate file handle
47h get current directory
48h allocate memory
49h release allocated memory
4Ah modify allocated memory
4Bh load or execute a program
4Ch terminate prog and return to DOS
4Dh get return code of subprocess created by 4Bh
4Eh find first matching file
4Fh find next matching file
50h* set new current Program Segment Prefix (PSP)
51h* puts current PSP into BX
52h* pointer to the DOS list of lists
53h* translates BPB (Bios Parameter Block, see below)
54h get disk verification status (VERIFY)
55h* create PSP: similar to function 26h
56h rename a file
57h get/set file date and time
58h get/set allocation strategy (DOS 3.x)
59h get extended error information
5Ah create a unique filename
5Bh create a DOS file
5Ch lock/unlock file contents
5Dh* network
5Eh* network printer
5Fh* network redirection
60h* parse pathname
61h* unknown
62h get program segment prefix (PSP)
63h* get lead byte table (DOS 2.25)
64h* unknown
65h get extended country information (DOS 3.3)
66h get/set global code page table (DOS 3.3)
67h set handle count (DOS 3.3)
68h commit file (DOS 3.3)
69h disk serial number (DOS 4.0)
6Ah unknown
6Bh unknown
6Ch extended open/create (DOS 4.0)
CALLING THE DOS SERVICES쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The DOS services are invoked by placing the number of the desired function in
register AH, subfunction in AL, setting the other registers to any specific
requirements of the function, and invoking int 21h.
On return, the requested service will be performed if possible. Most codes
will return an error; some return more information. Details are contained in
the listings for the individual functions. Extended error return may be
obtained by calling function 59h (see 59h).
Register settings listed are the ones used by DOS. Some functions will return
with garbage values in unused registers. Do not test for values in unspecified
registers; your program may exhibit odd behavior.
DS:DX pointers are the data segment register (DS) indexed to the DH and DL
registers (DX). DX always contains the offset address, DS contains the segment
address.
The File Control Block services (FCB services) were part of DOS 1.0. Since
the release of DOS 2.0, Microsoft has recommended that these services not be
used. A set of considerably more enhanced services (handle services) were
introduced with DOS 2.0. The handle services provide support for wildcards and
subdirectories, and enhanced error detection via function 59h.
The data for the following calls was compiled from various Intel, Microsoft,
IBM, and other publications. There are many subtle differences between MSDOS
and PCDOS and between the individual versions. Differences between the
versions are noted as they occur.
There are various ways of calling the DOS functions. For all methods, the
function number is loaded into register AH, subfunctions and/or parameters are
loaded into AL or other registers, and call int 21 by one of the following
methods:
A) call interrupt 21h directly (the recommended procedure)
B) perform a long call to offset 50h in the program's PSP.
1) This method will not work under DOS 1.x
2) Though recommended by Microsoft for DOS 2.0, this method takes more
time and is no longer recommended.
C) place the function number in CL and perform an intrasegment call to
location 05h in the current code segment. This location contains a long
call to the DOS function dispatcher.
1) IBM recommends this method be used only when using existing programs
written for different calling conventions. (such as converting CP/M
programs). This method should be avoided unless you have some specific
use for it.
2) AX is always destroyed by this method.
3) This method is valid only for functions 00h-24h.
There are also various ways of exiting from a program. (assuming it is not
intended to be a TSR). All methods except call 4Ch must ensure that the
segment register contains the segment address of the PSP.
A) Interrupt 21h, function 4Ch (Terminate with Result Code). This is the
"official" recommended method of returning to DOS.
B) Interrupt 21h, function 00h (Exit Program). This is the early style
int 21 function call. It simply calls int 20h.
C) Interrupt 20h (Exit).
D) A JMP instruction to offset 00h (int 20h vector) in the Program Segment
Prefix. This is just a roundabout method to call int 20h. This method
was set up in DOS 1.0 for ease of conversion for CP/M programs. It is no
longer recommended for use.
E) A JMP instruction to offset 05h (int 21 vector) in the Program Segment
Prefix, with AH set to 00h or 4Ch. This is another CP/M type function.
INT 21H DOS services
Function (hex)
* Indicates Functions not documented in the IBM DOS Technical Reference.
Note some functions have been documented in other Microsoft or licensed OEM
documentation.
Function 00h Terminate Program
Ends program, updates, FAT, flushes buffers, restores registers
entry AH 00h
CS segment address of PSP
return none
note 1) Program must place the segment address of the PSP control block in CS
before calling this function.
2) The terminate, ctrl-break,and critical error exit addresses (0Ah, 0Eh,
12h) are restored to the values they had on entry to the terminating
program, from the values saved in the program segment prefix at
locations PSP:000Ah, PSP:000Eh, and PSP:0012h.
3) All file buffers are flushed and the handles opened by the process are
closed.
4) Any files that have changed in length and are not closed are not
recorded properly in the directory.
5) Control transfers to the terminate address.
6) This call performs exactly the same function as int 20h.
7) All memory used by the program is returned to DOS.
Function 01h Get Keyboard Input
Waits for char at STDIN (if nescessary), echoes to STDOUT
entry AH 01h
return AL ASCII character from STDIN (8 bits)
note 1) Checks char for Ctrl-C, if char is Ctrl-C, executes int 23h.
2) For function call 06h, extended ASCII codes require two function calls.
The first call returns 00h as an indicator that the next call will be an
extended ASCII code.
3) Input and output are redirectable. If redirected, there is no way to
detect EOF.
Function 02h Display Output
Outputs char in DL to STDOUT
entry AH 02h
DL 8 bit data (usually ASCII character)
return none
note 1) If char is 08 (backspace) the cursor is moved 1 char to the left
(nondestructive backspace).
2) If Ctrl-C is detected after input, int 23h is executed.
3) Input and output are redirectable. If redirected, there is no way to
detect disk full.
Function 03h Auxiliary Input
Get (or wait until) character from STDAUX
entry AH 03h
return AL char from auxiliary device
note 1) AUX, COM1, COM2 is unbuffered and not interrupt driven
2) This function call does not return status or error codes. For greater
control it is recommended that you use ROM BIOS routine (int 14h) or
write an AUX device driver and use IOCTL.
3) At startup, PC-DOS initializes the first auxiliary port (COM1) to 2400
baud, no parity, one stop bit, and an 8-bit word. MSDOS may differ.
4) If Ctrl-C is has been entered from STDIN, int 23h is executed.
Function 04h Auxiliary Output
Write character to STDAUX
entry AH 04h
DL char to send to AUX
return none
note 1) This function call does not return status or error codes. For greater
control it is recommended that you use ROM BIOS routine (int 14h) or
write an AUX device driver and use IOCTL.
2) If Ctrl-C is has been entered from STDIN, int 23h is executed.
3) Default is COM1 unless redirected by DOS.
4) If the device is busy, this function will wait until it is ready.
Function 05h Printer Output
Write character to STDPRN
entry AL 05h
DL character to send
return none
note 1) If Ctrl-C is has been entered from STDIN, int 23h is executed.
2) Default is PRN or LPT1 unless redirected with the MODE command.
3) If the printer is busy, this function will wait until it is ready.
Function 06h Direct Console I/O
Get character from STDIN; echo character to STDOUT
entry AH 06h
DL 0FFh for console input, or 00h-0FEh for console output
return ZF set (1) = no character
clear (0) = character recieved
AL character
note 1) Extended ASCII codes require two function calls. The first call returns
00h to indicate the next call will return an extended code.
2) If DL is not 0FFh, DL is assumed to have a valid character that is
output to STDOUT.
3) This function does not check for Ctrl-C or Ctrl-PrtSc.
4) Does not echo input to screen
5) If I/O is redirected, EOF or disk full cannot be detected.
Function 07h Direct Console Input Without Echo (does not check BREAK)
Get or wait for char at STDIN, returns char in AL
entry AH 07h
return AL character from standard input device
note 1) Extended ASCII codes require two function calls. The first call returns
00h to indicate the next call will return an extended code.
2) No checking for Ctrl-C or Ctrl-PrtSc is done.
3) Input is redirectable.
Function 08h Console Input Without Echo (checks BREAK)
Get or Wait for char at STDIN, return char in AL
entry AH 08h
return AL char from standard input device
note 1) Char is checked for ctrl-C. If ctrl-C is detected, executes int 23h.
2) For function call 08h, extended ASCII characters require two function
calls. The first call returns 00h to signify an extended ASCII code.
The next call returns the actual code.
3) Input is redirectable. If redirected, there is no way to check EOF.
Function 09h Print String
Outputs Characters in the Print String to the STDOUT
entry AH 09h
DS:DX pointer to the Character String to be displayed
return none
note 1) The character string in memory must be terminated by a $ (24h)
The $ is not displayed.
2) Output to STDOUT is the same as function call 02h.
Function 0Ah Buffered Keyboard Input
Reads characters from STDIN and places them in the buffer beginning
at the third byte.
entry AH 0Ah
DS:DX pointer to an input buffer
return none
note 1) Min buffer size = 1, max = 255
2) Char is checked for ctrl-C. If ctrl-C is detected, executes int 23h.
3) Format of buffer DX:
byte contents
1 Maximum number of chars the buffer will take, including CR.
Reading STDIN and filling the buffer continues until a carriage
return ( or 0Dh) is read. If the buffer fills to one less
than the maximum number the buffer can hold, each additional
number read is ignored and ASCII 7 (BEL) is output to the
display until a carriage return is read. (you must set this
value)
2 Actual number of characters received, excluding the carriage
return, which is always the last character. (the function sets
this value)
3-n Characters received are placed into the buffer starting here.
Buffer must be at least as long as the number in byte 1.
4) Input is redirectable. If redirected, there is no way to check EOF.
5) The string may be edited with the standard DOS editing commands as it
is being entered.
6) Extended ASCII characters are stored as 2 bytes, the first byte being
zero.
Function 0Bh Check Standard Input (STDIN) status
Checks for character availible at STDIN
entry AH 0Bh
return AL 0FFh if a character is availible from STDIN
00h if no character is availible from STDIN
note 1) Checks for Ctrl-C. If Ctrl-C is detected, int 23h is executed
2) Input can be redirected.
3) Checks for character only, it is not read into the application
4) IBM reports that this call does not work properly under the DOSSHELL
program in DOS 4.00 and 4.01. DOSSHELL will return all zeroes. This
function works correctly from the command line or application.
Function 0Ch Clear Keyboard Buffer & Invoke a Keyboard Function (FCB)
Dumps buffer, executes function in AL (01h,06h,07h,08h,0Ah only)
entry AH 0Ch
AL function number (must be 01h, 06h, 07h, 08h, or 0Ah)
return AL 00h buffer was flushed, no other processing performed
other any other value has no meaning
note 1) Forces system to wait until a character is typed.
2) Flushes all typeahead input, then executes function specified by AL (by
moving it to AH and repeating the int 21 call).
3) If AL contains a value not in the list above, the keyboard buffer is
flushed and no other action is taken.
Function 0Dh Disk Reset
Flushes all currently open file buffers to disk
entry AH 0Dh
return none
note 1) Does not close files. Does not update directory entries; files changed
in size but not closed are not properly recorded in the directory
2) Sets DTA address to DS:0080h
3) Should be used before a disk change, Ctrl-C handlers, and to flush
the buffers to disk.
Function 0Eh Select Disk
Sets the drive specified in DL (if valid) as the default drive
entry AL 0Eh
DL new default drive number (0=A:,1=B:,2=C:,etc.)
return AL total number of logical drives (not nescessarily physical)
note 1) For DOS 1.x and 2.x, the minimum value for AL is 2.
2) For DOS 3.x and 4.x, the minimum value for AL is 5.
3) The drive number returned is not nescessarily a valid drive.
4) For DOS 1.x: 16 logical drives are availible, A-P.
For DOS 2.x: 63 logical drives are availible. (Letters are only used for
the first 26 drives. If more than 26 logical drives are
used, further drive letters will be other ASCII characters
ie {,], etc.
For DOS 3.x: 26 logical drives are availible, A-Z.
For DOS 4.x: 26 logical drives are availible, A-Z.
Function 0Fh Open Disk File (FCB)
Searches current directory for specified filename and opens it
entry AH 0Fh
DS:DX pointer to an unopened FCB
return AL 00h if file found
0FFh if file not not found
note 1) If the drive code was 0 (default drive) it is changed to the actual
drive used (1=A:,2=B:,3=C:, etc). This allows changing the default drive
without interfering with subsequent operations on this file.
2) The current block field (FCB bytes C-D, offset 0Ch) is set to zero.
3) The size of the record to be worked with (FCB bytes E-F, offset 0Eh) is
set to the system default of 80h. The size of the file (offset 10h) and
the date (offset 14h) are set from information obtained in the root
directory. You can change the default value for the record size (FCB
bytes E-F) or set the random record size and/or current record field.
Perform these actions after the open but before any disk operations.
4) The file is opened in compatibility mode.
5) Microsoft recommends handle function call 3Dh be used instead.
6) This call is also used by the APPEND command in DOS 3.2+
7) Before performing a sequential disk operation on the file, you must
set the Current Record field (offset 20h). Before performing a random
disk operation on the file, you must set the Relative Record field
(offset 21h). If the default record size of 128 bytes is incorrect, set
it to the correct value.
Function 10h Close File (FCB)
Closes a File After a File Write
entry AH 10h
DS:DX pointer to an opened FCB
return AL 00h if the file is found and closed
0FFh if the file is not found in the current directory
note 1) This function call must be done on open files that are no longer needed,
and after file writes to insure all directory information is updated.
2) If the file is not found in its correct position in the current
directory, it is assumed that the diskette was changed and AL returns
0FFh. This error return is reportedly not completely reliable with DOS
version 2.x.
3) If found, the directory is updated to reflect the status in the FCB, the
buffers to that file are flushed, and AL returns 00h.
Function 11h Search For First Matching Entry (FCB)
Searches current disk & directory for first matching filename
entry AH 11h
DS:DX pointer to address of FCB
return AL 00h successful match
0FFh no matching filename found
note 1) The FCB may contain the wildcard character ? under Dos 2.x, and ? or *
under 3.x and 4.x.
2) The original FCB at DS:DX contains information to continue the search
with function 12h, and should not be modified.
3) If a matching filename is found, AL returns 00h and the locations at the
Disk Transfer Address are set as follows:
a) If the FCB provided for searching was an extended FCB, then the first
byte at the disk transfer address is set to 0FFh followed by 5 bytes
of zeroes, then the attribute byte from the search FCB, then the
drive number used (1=A, 2=B, etc) then the 32 bytes of the directory
entry. Thus, the disk transfer address contains a valid unopened FCB
with the same search attributes as the search FCB.
b) If the FCB provided for searching was a standard FCB, then the first
byte is set to the drive number used (1=A,2=b,etc), and the next 32
bytes contain the matching directory entry. Thus, the disk transfer
address contains a valid unopened normal FCB.
4) If an extended FCB is used, the following search pattern is used:
a) If the FCB attribute byte is zero, only normal file entries are
found. Entries for volume label, subdirectories, hidden or system
files, are not returned.
b) If the attribute byte is set for hidden or system files, or
subdirectory entries, it is to be considered as an inclusive search.
All normal file entries plus all entries matching the specified
attributes are returned. To look at all directory entries except the
volume label, the attribute byte may be set to hidden + system +
directory (all 3 bits on).
c) If the attribute field is set for the volume label, it is considered
an exclusive search, and ONLY the volume label entry is returned.
5) This call is also used by the APPEND command in DOS 3.2+
Function 12h Search For Next Entry Using FCB (FCB)
Search for next matching filename
entry AH 12h
DS:DX pointer to the unopened FCB specified from the previous Search
First (11h) or Search Next (12h)
return AL 00h if matching filename found
0FFh if matching filename was not found
note 1) After a matching filename has been found using function call 11h,
function 12h may be called to find the next match to an ambiguous
request. For DOS 2.x, ?'s are allowed in the filename. For DOS 3.x
and 4.x, global (*) filename characters are allowed.
2) The DTA contains info from the previous Search First or Search Next.
3) All of the FCB except for the name/extension field is used to keep
information nescessary for continuing the search, so no disk operations
may be performed with this FCB between a previous function 11h or 12h
call and this one.
4) If the file is found, an FCB is created at the DTA address and set up to
open or delete it.
Function 13h Delete File Via FCB (FCB)
Deletes file specified in FCB from current directory
entry AH 13h
DS:DX pointer to address of FCB
return AL 00h file deleted
0FFh if file not found or was read-only
note 1) All matching current directory entries are deleted. The global filename
character "?" is allowed in the filename.
2) Will not delete files with read-only attribute set
3) Close open files before deleting them.
4) Requires Network Access Rights
Function 14h Sequential Disk File Read (FCB)
Reads record sequentially from disk via FCB
entry AH 14h
DS:DX pointer to an opened FCB
return AL 00h successful read
01h end of file (no data read)
02h Data Transfer Area too small for record size specified
or segment overflow
03h partial record read, EOF found
note 1) The record size is set to the value at offset 0Eh in the FCB.
2) The record pointed to by the Current Block (offset 0Ch) and the Current
Record (offset 20h) fields is loaded at the DTA, then the Current Block
and Current Record fields are incremented.
3) The record is read into memory at the current DTA address as specified
by the most recent call to function 1Ah. If the size of the record and
location of the DTA are such that a segment overflow or wraparound would
occur, the error return is set to AL=02h
4) If a partial record is read at the end of the file, it is passed to the
requested size with zeroes and the error return is set to AL=03h.
Function 15h Sequential Disk Write (FCB)
Writes record specified by FCB sequentially to disk
entry AH 15h
DS:DX pointer to address of FCB
return AL 00h successful write
01h diskette full, write canceled
02h disk transfer area (DTA) too small or segment wrap
note 1) The data to write is obtained from the disk transfer area
2) The record size is set to the value at offset 0Eh in the FCB.
3) This service cannot write to files set as read-only
4) The record pointed to by the Current Block (offset 0Ch) and the Current
Record (offset 20h) fields is loaded at the DTA, then the Current Block
and Current Record fields are incremented.
5) If the record size is less than a sector, the data in the DTA is written
to a buffer; the buffer is written to disk when it contains a full
sector of data, the file is closed, or a Reset Disk (function 0Dh) is
issued.
6) The record is written to disk at the current DTA address as specified
by the most recent call to function 1Ah. If the size of the record and
location of the DTA are such that a segment overflow or wraparound would
occur, the error return is set to AL=02h
Function 16h Create A Disk File (FCB)
Search and open or create directory entry for file
entry AH 16h
DS:DX pointer to an FCB
return AL 00h successful creation
0FFh no room in directory
note 1) If a matching directory entry is found, the file is truncated to zero
bytes.
2) If there is no matching filename, a filename is created.
3) This function calls function 0Fh (Open File) after creating or
truncating a file.
4) A hidden file can be created by using an extended FCB with the attribute
byte (offset FCB-1) set to 2.
Function 17h Rename File Specified by File Control Block (FCB)
Renames file in current directory
entry AH 17h
DS:DX pointer to an FCB (see note 4)
return AL 00h successfully renamed
0FFh file not found or filename already exists
note 1) This service cannot rename read-only files
2) The "?" wildcard may be used.
3) If the "?" wildcard is used in the second filename, the corresponding
letters in the filename of the directory entry are not changed.
4) The FCB must have a drive number, filename, and extension in the usual
position, and a second filename starting 6 bytes after the first, at
offset 11h.
5) The two filenames cannot have the same name.
6) FCB contains new name starting at byte 17h.
Function 18h Internal to DOS
* Unknown
entry AH 18h
return AL 0
Function 19h Get Current Disk Drive
Return designation of current default disk drive
entry AH 19h
return AL current default drive (0=A, 1=B,etc.)
note Some other DOS functions use 0 for default, 1=A, 2=B, etc.
Function 1Ah Set Disk Transfer Area Address (DTA)
Sets DTA address to the address specified in DS:DX
entry AH 1Ah
DS:DX pointer to buffer
return none
note 1) The default DTA is 128 bytes at offset 80h in the PSP. DOS uses the
DTA for all file I/O.
2) Registers are unchanged.
3) No error codes are returned.
2) Disk transfers cannot wrap around from the end of the segment to the
beginning or overflow into another segment.
Function 1Bh Get Current Drive File Allocation Table Information
Returns information from the FAT on the current drive
entry AH 1Bh
exit AL number of sectors per allocation unit (cluster)
DS:BX address of the current drive's media descriptor byte
CX number of bytes per sector
DX number of allocation units (clusters) for default drive
note 1) Save DS before calling this function.
2) This call returned a pointer to the FAT in DOS 1.x. Beginning with
DOS 2.00, it returns a pointer only to the table's ID byte.
3) IBM recommends programmers avoid this call and use int 25h instead.
Function 1Ch Get File Allocation Table Information for Specific Device
Returns information on specified drive
entry AH 1Ch
DL drive number (1=A, 2=B, 3=C, etc)
return AL number of sectors per allocation unit (cluster)
DS:BX address of media descriptor byte for drive in DL
CX sector size in bytes
DX number of allocation units (clusters)
note 1) DL = 0 for default.
2) Save DS before calling this function.
3) Format of media-descriptor byte:
bits: 0 0 (clear) not double sided
1 (set) double sided
1 0 (clear) not 8 sector
1 (set) 8 sector
2 0 (clear) nonremovable device
1 (set) removable device
3-7 always set (1)
4) This call returned a pointer to the FAT in DOS 1.x. Beginning with
DOS 2.00, it returns a pointer only to the table's ID byte.
5) IBM recommends programmers avoid this call and use int 25h instead.
Function 1Dh Not Documented by Microsoft
* Unknown
entry AH 1Dh
return AL 0
Function 1Eh Not Documented by Microsoft
* Unknown
entry AH 1Eh
return AL 0
note Apparently does nothing
Function 1Fh Get Default Drive Parameter Block
* Same as function call 32h (below), except that the table is accessed from
the default drive
entry AH 1Fh
other registers unknown
return AL 00h no error
0FFh error
DS:BX points to DOS Disk Parameter Block for default drive.
note 1) Unknown vector returned in ES:BX.
2) For DOS 2.x and 3.x, this just invokes function 32h (undocumented,
Read DOS Disk Block) with DL=0
Function 20h Unknown
* Internal - does nothing?
entry AH 20h
return AL 0
Function 21h Random Read from File Specified by File Control Block (FCB)
Reads one record as specified in the FCB into the current DTA.
entry AH 21h
DS:DX address of the opened FCB
return AL 00h successful read operation
01h end of file (EOF), no data read
02h DTA too small for the record size specified
03h end of file (EOF), partial data read
note 1) The current block and current record fields are set to agree with the
random record field. Then the record addressed by these fields is read
into memory at the current Disk Transfer Address.
2) The current file pointers are NOT incremented this function.
3) If the DTA is larger than the file, the file is padded to the requested
length with zeroes.
Function 22h Random Write to File Specified by FCB (FCB)
Writes one record as specified in the FCB to the current DTA
entry AH 22h
DS:DX address of the opened FCB
return AL 00h successful write operation
01h disk full; no data written (write was canceled)
02h DTA too small for the record size specified (write was
canceled)
note 1) This service cannot write to read-only files.
2) The record pointed to by the Current Block (offset 0Ch) and the Current
Record (offset 20h) fields is loaded at the DTA, then the Current Block
and Current Record fields are incremented.
3) If the record size is less than a sector, the data in the DTA is written
to a buffer; the buffer is written to disk when it contains a full
sector of data, the file is closed, or a Reset Disk (function 0Dh) is
issued.
4) The current file pointers are NOT incremented this function.
5) The record is written to disk at the current DTA address as specified
by the most recent call to function 1Ah. If the size of the record and
location of the DTA are such that a segment overflow or wraparound would
occur, the error return is set to AL=02h
Function 23h Get File Size (FCB)
Searches current subdirectory for matching file, returns size in FCB
entry AH 23h
DS:DX address of an unopened FCB
return AL 00h file found
0FFh file not found
note 1) Record size field (offset 0Eh) must be set before invoking this function
2) The disk directory is searched for the matching entry. If a matching
entry is found, the random record field is set to the number of records
in the file. If the value of the Record Size field is not an even
divisor of the file size, the value set in the relative record field is
rounded up. This gives a returned value larger than the actual file size
3) This call is used by the APPEND command in DOS 3.2+
Function 24h Set Relative Record Field (FCB)
Set random record field specified by an FCB
entry AH 24h
DS:DX address of an opened FCB
return Random Record Field of FCB is set to be same as Current Block
and Current Record.
note 1) You must invoke this function before performing random file access.
2) The relative record field of FCB (offset 21h) is set to be same as the
Current Block (offset 0Ch) and Current Record (offset 20h).
3) No error codes are returned.
4) The FCB must already be opened.
Function 25h Set Interrupt Vector
Sets the address of the code DOS is to perform each time the specified
interrupt is invoked.
entry AH 25h
AL int number to reassign the handler to
DS:DX address of new interrupt vector
return none
note 1) Registers are unchanged.
2) No error codes are returned.
3) The interrupt vector table for the interrupt number specified in AL
is set to the address contained in DS:DX. Use function 35h (Get Vector)
to get the contents of the interrupt vector and save it for later use.
4) When you use function 25 to set an interrupt vector, DOS 3.2 doesn't
point the actual interrupt vector to what you requested. Instead, it
sets the interrupt vector to point to a routine inside DOS, which does
this:
1. Save old stack pointer
2. Switch to new stack pointer allocated from DOS's stack pool
3. Call your routine
4. Restore old stack pointer
The purpose for this was to avoid possible stack overflows when there
are a large number of active interrupts. IBM was concerned (this was an
IBM change, not Microsoft) that on a Token Ring network there would be
a lot of interrupts going on, and applications that hadn't allocated
very much stack space would get clobbered.
Function 26h Create New Program Segment Prefix (PSP)
This service copies the current program-segment prefix to a new memory
location for the creation of a new program or overlay. Once the new PSP is
in place, a DOS program can read a DOS COM or overlay file into the memory
location immediately following the new PSP and pass control to it.
entry AH 26h
DX segment number for the new PSP
return none
note 1) Microsoft recommends you use the newer DOS service 4Bh (EXEC) instead.
2) The entire 100h area at location 0 in the current PSP is copied into
location 0 of the new PSP. The memory size information at location 6
in the new segment is updated and the current termination, ctrl-break,
and critical error addresses from interrupt vector table entries for
ints 22h, 23h, and 24 are saved in the new program segment starting at
0Ah. They are restored from this area when the program terminates.
3) Current PSP is copied to specified segment
Function 27h Random Block Read From File Specified by FCB
Similar to 21h (Random Read) except allows multiple files to be read.
entry AH 27h
CX number of records to be read
DS:DX address of an opened FCB
return AL 00h successful read
01h end of file, no data read
02h DTA too small for record size specified (read canceled)
03h end of file
CX actual number of records read (includes partial if AL=03h)
note 1) The record size is specified in the FCB. The service updates the Current
Block (offset 0Ch) and Current Record (offset 20h) fields to the next
record not read.
2) If CX contained 0 on entry, this is a NOP.
3) If the DTA is larger than the file, the file is padded to the requested
length with zeroes.
4) This function assumes that the FCB record size field (0Eh) is correctly
set. If not set by the user, the default is 128 bytes.
5) The record is written to disk at the current DTA address as specified
by the most recent call to function 1Ah. If the size of the record and
location of the DTA are such that a segment overflow or wraparound would
occur, the error return is set to AL=02h
Function 28h Random Block Write to File Specified in FCB
Similar to 27h (Random Write) except allows multiple files to be read.
entry AH 28h
CX number of records to write
DS:DX address of an opened FCB
return AL 00h successful write
01h disk full, no data written
02h DTA too small for record size specified (write canceled)
CX number of records written
note 1) The record size is specified in the FCB.
2) This service allocates disk clusters as required.
3) This function assumes that the FCB Record Size field (offset 0Eh) is
correctly set. If not set by the user, the default is 128 bytes.
4) The record size is specified in the FCB. The service updates the Current
Block (offset 0Ch) and Current Record (offset 20h) fields to the next
record not read.
5) The record is written to disk at the current DTA address as specified
by the most recent call to function 1Ah. If the size of the record and
location of the DTA are such that a segment overflow or wraparound would
occur, the error return is set to AL=02h
6) If called with CX=0, no records are written, but the FCB's File Size
entry (offset 1Ch) is set to the size specified by the FCB's Relative
Record field (offset 21h).
Function 29h Parse the Command Line for Filename
Parses a text string into the fields of a File Control Block
entry AH 29h
DS:SI pointer to string to parse
ES:DI pointer to memory buffer to fill with unopened FCB
AL bit mask to control parsing
bit 0 = 0: parsing stops if file seperator found
1: causes service to scan past leading chars such as
blanks. Otherwise assumes the filename begins in
the first byte
1 = 0: drive number in FCB set to default (0) if string
contains no drive number
1: drive number in FCB not changed
2 = 0: filename in FCB set to 8 blanks if no filename in
string
1: filename in FCB not changed if string does not
contain a filename
3 = 0: extension in FCB set to 3 blanks if no extension in
string
1: extension left unchanged
4-7 must be zero
return AL 00h no wildcards in name or extension
01h wildcards appeared in name or extension
0FFh invalid drive specifier
DS:SI pointer to the first byte after the parsed string
ES:DI pointer to a buffer filled with the unopened FCB
note 1) If the * wildcard characters are found in the command line, this service
will replace all subsequent chars in the FCB with question marks.
2) This service uses the characters as filename separators
DOS 1 : ; . , + / [ ] = " TAB SPACE
DOS 2,3 : ; . , + = TAB SPACE
3) This service uses the characters
: ; . , + < > | / \ [ ] = " TAB SPACE
or any control characters as valid filename separators
4) A filename cannot contain a filename terminator. If one is encountered,
all processing stops. The handle functions will allow use of some of
these characters.
5) If no valid filename was found on the command line, ES:DI +1 points
to a blank (ASCII 32).
6) This function cannot be used with filespecs which include a path
7) Parsing is in the form D:FILENAME.EXT. If one is found, a corresponding
unopened FCB is built at ES:DI
Function 2Ah Get Date
Returns day of the week, year, month, and date
entry AH 2Ah
return CX year (1980-2099)
DH month (1-12)
DL day (1-31)
AL weekday 00h Sunday
01h Monday
02h Tuesday
03h Wednesday
04h Thursday
05h Friday
06h Saturday
note 1) Date is adjusted automatically if clock rolls over to the next day,
and takes leap years and number of days in each month into account.
2) Although DOS cannot set an invalid date, it can read one, such as
1/32/80, etc.
3) DesQview also accepts CX = 4445h and DX = 5351h, i.e. 'DESQ' as valid
4) DOS will accept CH=0 (midnight) as a valid time, but if a file's time
is set to exactly midnight the time will not be displayed by the DIR
command.
Function 2Bh Set Date
set current system date
entry AH 2Bh
CX year (1980-2099)
DH month (1-12)
DL day (1-31)
return AL 00h no error (valid date)
0FFh invalid date specified
note 1) On entry, CX:DX must have a valid date in the same format as returned
by function call 2Ah
2) DOS 3.3 also sets CMOS clock
Function 2Ch Get Time
Get current system time from CLOCK$ driver
entry AH 2Ch
return CH hours (0-23)
CL minutes (0-59)
DH seconds (0-59)
DL hundredths of a second (0-99)
note 1) Time is updated every 5/100 second.
2) The date and time are in binary format
Function 2Dh Set Time
Sets current system time
entry AH 2Dh
CH hours (0-23)
CL minutes (0-59)
DH seconds (0-59)
DL hundredths of seconds (0-99)
return AL 00h if no error
0FFh if bad value sent to routine
note 1) DOS 3.3 also sets CMOS clock
2) CX and DX must contain a valid time in binary
Function 2Eh Set/Reset Verify Switch
Set verify flag
entry AH 2Eh
AL 00 to turn verify off (default)
01 to turn verify on
return none
note 1) This is the call invoked by the DOS VERIFY command
2) Setting of the verify switch can be obtained by calling call 54h
3) This call is not supported on network drives
4) DOS checks this flag each time it accesses a disk
Function 2Fh Get Disk Transfer Address (DTA)
Returns current disk transfer address used by all DOS read/write operations
entry AH 2Fh
return ES:BX address of DTA
note 1) The DTA is set by function call 1Ah
2) Default DTA address is a 128 byte buffer at offset 80h in that program's
Program Segment Prefix
Function 30h Get DOS Version Number
Return DOS version and/or user number
entry AH 30h
return AH minor version number (i.e., DOS 2.10 returns AX = 0A02h)
AL major version number
BH OEM ID number
00h IBM
16h DEC (others not known)
BL:CX 24-bit user serial number
note 1) If AL returns a major version number of zero, the DOS version is
below 1.28 for MSDOS and below 2.00 for PCDOS.
2) IBM PC-DOS always returns 0000h in BX and CX.
3) OS/2 v1.0 Compatibility Box returns a value of 10 for major version.
4) Due to the OS/2 return and the fact that some European versions of DOS
carry higher version numbers than IBM's DOS, utilities which check
for a DOS version should not abort if a higher version than required
is found unless some specific problems are known.
Function 31h Terminate Process and Stay Resident
KEEP, or TSR
entry AH 31h
AL exit code
DX program memory requirement in 16 byte paragraphs
return AX return code (retrieveable by function 4Dh)
note 1) Files opened by the application are not closed when this call is made
2) Memory can be used more efficiently if the block containing the copy of
the DOS environment is deallocated before terminating. This can be done
by loading ES with the segment contained in 2Ch of the PSP and issuing
function call 49h (Free Allocated Memory).
3) Unlike int 27h, more than 64k may be made resident with this call
Function 32h Read DOS Disk Block
* Retrieve the pointer to the drive parameter block for a drive
entry AH 32h
DL drive (0=default, 1=A:, etc.).
return AL 00h if drive is valid
0FFh if drive is not valid
DS:BX pointer to DOS Drive Parameter Table. Format of block:
Bytes Type Value
00h byte Drive: 0=A:, 1=B:, etc.
01h byte Unit within drive (0, 1, 2, etc.)
02h-03h word Bytes per sector
04h byte Sectors per cluster - 1
05h byte Cluster to sector shift (i.e., how far to shift-
left the bytes/sector to get bytes/cluster)
06h-07h word Number of reserved (boot) sectors
08h byte Number of FATs
09h-0Ah word Number of root directory entries
0Bh-0Ch word Sector # of 1st data. Should be same as # of
sectors/track.
0Dh-0Eh word # of clusters + 1 (=last cluster #)
0Fh byte Sectors for FAT
10h-11h word First sector of root directory
12h-15h dword Address of device driver header for this drive
16h byte Media Descriptor Byte for this drive
17h byte 0FFh indicates block must be rebuilt
(DOS 3.x) 00h indicates block device has
been accessed
18h-1Bh dword address of next DOS Disk Block (0FFFFh means
last in chain)
22h byte Current Working Directory (2.0 only) (64 bytes)
note 1) Use [BX+0D] to find no. of clusters (>1000H, 16-bit FAT; if not, 12-bit
(exact dividing line is probably a little below 1000h to allow for
bad sectors, EOF markers, etc.)
2) Short article by C.Petzold, PC Magazine Vol.5,no.8, and the article
"Finding Disk Parameters" in the May 1986 issue of PC Tech Journal.
3) This call is mostly supported in OS/2 1.0's DOS Compatibility Box. The
dword at 12h will not return the address of the next device driver when
in the Compatibility Box.
4) used by CHKDSK
Function 33h Control-Break Check
Get or set control-break checking at CON
entry AH 33h
AL 00h to test for break checking
01h to set break checking
DL 00h to disable break checking
01h to enable break checking
02h internal, called by PRINT.COM (DOS 3.1)
03h unknown
04h unknown
05h boot drive (DOS 4.0+)
return DL 00h if break=off
01h if break=on
(if AL=05h) boot drive, A=1, B=2, etc)
AL 0FFh error
Function 34h Return INDOS Flag
* Returns ES:BX pointing to Critical Section Flag, byte indicating whether
it is safe to interrupt DOS.
entry AH 34h
return ES:BX points to DOS "critical section flag"
note 1) If byte is 0, it is safe to interrupt DOS. This was mentioned in some
documentation by Microsoft on a TSR standard, and PC Magazine reports
it functions reliably under DOS versions 2.0 through 3.3. Chris
Dunford (of CED fame) and a number of anonymous messages on the BBSs
indicate it may not be totally reliable.
2) The byte at ES:BX+1 is used by the Print program for this same purpose,
so it's probably safer to check the WORD at ES:BX.
3) Reportedly, examination of DOS 2.10 code in this area indicates that the
byte immediately following this "critical section flag" must be 00h to
permit the PRINT.COM interrupt to be called. For DOS 3.0 and 3.1 (except
Compaq DOS 3.0), the byte before the "critical section flag" must be
zero; for Compaq DOS 3.0, the byte 01AAh before it must be zero.
4) In DOS 3.10 this reportedly changed to word value, with preceding byte.
5) This call is supported in OS/2 1.0's DOS Compatibility Box
6) Gordon Letwin of Microsoft discussed this call on ARPAnet in 1984. He
stated:
a) this is not supported under any version of the DOS
b) it usually works under DOS 2, but there may be circumstances
when it doesn't (general disclaimer, don't know of a specific
circumstance)
c) it will usually not work under DOS 3 and DOS 3.1; the DOS is
considerably restructured and this flag takes on additional
meanings and uses
d) it will fail catastrophically under DOS 4.0 and forward.
Obviously this information is incorrect since the call works fine
through DOS 3.3. Microsoft glasnost?
Function 35h Get Vector
Get interrupt vector
entry AH 35h
AL interrupt number (hexadecimal)
return ES:BX address of interrupt vector
note Use function call 25h to set the interrupt vectors
Function 36h Get Disk Free Space
get information on specified drive
entry AH 36h
DL drive number (0=default, 1=A:, 2=B:, etc)
return AX number of sectors per cluster
0FFFFh means drive specified in DL is invalid
BX number of availible clusters
CX bytes per sector
DX clusters per drive
note 1) Mult AX * CX * BX for free space on disk
2) Mult AX * CX * DX for total disk space
3) Function 36h returns an incorrect value after an ASSIGN command. Prior
to ASSIGN, the DX register contains 0943h on return, which is the free
space in clusters on the HC diskette. After ASSIGN, even with no
parameters, 0901h is returned in the DX register; this is an incorrect
value. Similar results occur with DD diskettes on a PC-XT or a PC-AT.
This occurs only when the disk is not the default drive. Results are as
expected when the drive is the default drive. Therefore, the
circumvention is to make the desired drive the default drive prior to
issuing this function call.
4) Int 21h, function call 36h returns an incorrect value after an ASSIGN
command. Prior to ASSIGN, the DX register contains 0943h on return,
which is the free space in clusters on the HC diskette. After ASSIGN,
even with no parameters, 0901h is returned in the DX register; this is
an incorrect value. Similar results occur with DD diskettes on a PC-XT
or a PC-AT. This occurs only when the disk is not the default drive.
Results are as expected when the drive is the default drive. Therefore,
the circumvention is to make the desired drive the default drive prior
to issuing this function call.
5) This function supercedes functions 1Bh and 1Ch.
Function 37h SWITCHAR / AVAILDEV
* Get/set option marking character (is usually "/"), and device type
entry AH 37h
AL 00h read switch character (returns current character in DL)
01h set character in DL as new switch character
(DOS 2.x) 02h read device availability (as set by function AL=3) into
DL. A 0 means devices that devices must be accessed in
file I/O calls by /dev/device. A non-zero value means
that devices are accessible at every level of the
directory tree (e.g., PRN is the printer and not a file
PRN).
AL=2 to return flag in DL, AL=3 to set from DL (0 = set,
1 = not set).
(DOS 2.x) 03h get device availability, where:
DL 00h means /dev/ must precede device names
01h means /dev/ need not precede device names
return DL switch character (if AL=0 or 1)
device availability flag (if AL=2 or 3)
AL 0FFh the value in AL was not in the range 0-3.
note 1) Functions 2 & 3 appear not to be implemented for DOS 3.x.
2) It is documented on page 4.324 of the MS-DOS (version 2) Programmer's
Utility Pack (Microsoft - published by Zenith).
3) Works on all versions of IBM PC-DOS from 2.0 through 3.3.1.
4) The SWITCHAR is the character used for "switches" in DOS command
arguments (defaults to '/', as in "DIR/P"). '-' is popular to make a
system look more like UNIX; if the SWITCHAR is anything other than '/',
then '/' may be used instead of '\' for pathnames
5) Ignored by XCOPY, PKARC, LIST
6) SWITCHAR may not be set to any character used in a filename
7) In DOS 3.x you can still read the "AVAILDEV" byte with subfunction 02h
but it always returns 0FFh even if you try to change it to 0 with
subfunction 03h.
8) AVAILDEV=0 means that devices must be referenced in an imaginary
subdirectory "\dev" (similar to UNIX's /dev/*); a filename "PRN.DAT"
can be created on disk and manipulated like any other. If AVAILDEV != 0
then device names are recognized anywhere (this is the default):
"PRN.DAT" is synonymous with "PRN:".
9) These functions reportedly are not supported in the same fashion in
various implementations of DOS.
10) used by DOS 3.3 CHKDSK, BASIC, DEBUG
Function 38h Return Country Dependent Information
(PCDOS 2.0, 2.1, MSDOS 2.00 only)
entry AH 38h
AL function code (must be 0 in DOS 2.x)
DS:DX pointer to 32 byte memory buffer for returned information
return CF set on error
AX error code (02h)
BX country code
DS:DX pointer to buffer filled with country information:
bytes 0,1 date/time format
0 USA standard H:M:S M/D/Y
1 European standard H:M:S D/M/Y
2 Japanese standard H:M:S D:M:Y
byte2 ASCIIZ string currency symbol
byte3 zeroes
byte4 ASCIIZ string thousands separator
byte5 zeroes
byte6 ASCIIZ string decimal separator
byte7 zeroes
bytes 8,1Fh 24 bytes reserved
Function 38h Get Country Dependent Information
(PCDOS 3.x+, MSDOS 2.01+)
entry AH 38h
AL function code
00h to get current country information
01h-0FEh country code to get information for, for countries
with codes less than 255
0FFh to get country information for countries with a code
greater than 255
BX 16 bit country code if AL=0FFh
DS:DX pointer to the memory buffer where the data will be returned
DX 0FFFFh if setting country code rather than getting info
return CF 0 (clear) function completed
1 (set) error
AX error code
02h invalid country code (no table for it)
(if DX <> 0FFFFh)
BX country code (usually international telephone code)
DS:DX pointer to country data buffer
bytes 0,1 date/time format
0 USA standard H:M:S M/D/Y
1 European standard H:M:S D/M/Y
2 Japanese standard H:M:S D:M:Y
bytes 2-6 currency symbol null terminated
byte 07h thousands separator null terminated
byte 08h zeroes
byte 09h decimal separator null terminated
byte 0Ah zeroes
byte 0Bh date separator null terminated
byte 0Ch zeroes
byte 0Dh time separator null terminated
byte 0Eh zeroes
byte 0Fh bit field currency format
bit 0 = 0 if currency symbol precedes the value
1 if currency symbol is after the value
bit 1 = 0 no spaces between value and currency symbol
1 one space between value and currency symbol
bit 2 = 1 set if currency symbol replaces decimal pt
bits 3-7 not defined by Microsoft
byte 10h number of significant decimal digits in currency
(number of places to right of decimal point)
byte 11h time format
bit 0 = 0 12 hour clock
1 24 hour clock
bits 1-7 unknown, probably not used
bytes 12h-15h address of case map routine (FAR CALL, AL = char)
entry AL ASCII code of character to be converted to
uppercase
return AL ASCII code of the uppercase input character
byte 16h data-list separator character
byte 17h zeroes
bytes 18h-21h 5 words reserved
note 1) When an alternate keyboard handler is invoked, the keyboard routine is
loaded into user memory starting at the lowest portion of availible
user memory. The BIOS interrupt vector that services the keyboard is
redirected to the memory area where the new routine resides. Each new
routine takes up about 1.6K of memory and has lookup tables that return
values unique to each language. (KEYBxx in the DOS book)
Once the keyboard interrupt vector is changed by the DOS keyboard
routine, the new routine services all calls unless the system is
returned to the US format by the ctrl-alt-F1 keystroke combination. This
does not change the interrupt vector back to the BIOS location; it
merely passes the table lookup to the ROM locations.
2) Ctrl-Alt-F1 will only change systems with US ROMS to the US layout.
Some systems are delivered with non-US keyboard handler routines in ROM
3) Case mapping call: the segment/offset of a FAR procedure that performs
country-specific lower-to-upper case mapping on ASCII characters 80h to
0FFh. It is called with the character to be mapped in AL. If there is
an uppercase code for the letter, it is returned in AL, if there is no
code or the function was called with a value of less than 80h AL is
returned unchanged.
4) This call is fully implemented in MS-DOS version 2.01 and higher. It
is in version 2.00 but not fully implemented (according to Microsoft)
Function 38h Set Country Dependent Information
entry AH 38h
AL code country code to set information for, for countries
with codes less than 255
0FFh to set country information for countries with a code
greater than 255
BX 16 bit country code if AL=0FFh
DX 0FFFFh
return CF clear successful
set if error
AX error code (02h)
Function 39h Create Subdirectory (MKDIR)
Makes a subdirectory along the indicated path
entry AH 39h
DS:DX address of ASCIIZ pathname string
return flag CF 0 successful
1 error
AX error code if any (3, 5)
note 1) The ASCIIZ string may contain drive and subdirectory.
2) Drive may be any valid drive (not nescessarily current drive)
3) The pathname cannot exceed 64 characters
Function 3Ah Remove Subdirectory (RMDIR)
entry AH 3Ah
DS:DX address of ASCIIZ pathname string
return CF clear successful
set AX error code if any (3, 5, 16)
note 1) The ASCIIZ string may contain drive and subdirectory.
2) Drive may be any valid drive (not nescessarily current drive)
3) The pathname cannot exceed 64 characters
Function 3Bh Change Current Directory (CHDIR)
entry AH 3Bh
DS:DX address of ASCIIZ string
return flag CF 0 successful
1 error
AX error code if any (3)
note 1) The pathname cannot exceed 64 characters
2) The ASCIIZ string may contain drive and subdirectory.
3) Drive may be any valid drive (not nescessarily current drive)
Function 3Ch Create A File (CREAT)
Create a file with handle
entry AH 3Ch
CX attributes for file
00h normal
01h read only
02h hidden
03h system
DS:DX address of ASCIIZ filename string
return flag CF 0 successful creation
1 error
AX 16 bit file handle
or error code (3, 4, 5)
note 1) The ASCIIZ string may contain drive and subdirectory.
2) Drive may be any valid drive (not nescessarily current drive)
3) If the volume label or subdirectory bits are set in CX, they are ignored
4) The file is opened in read/write mode
5) If the file does not exist, it is created. If one of the same name
exists, it is truncated to a length of 0.
6) Good practice is to attempt to open a file with fn 3Dh and jump to an
error routine if successful, create file if 3Dh fails. That way an
existing file will not be truncated and overwritten.
Function 3Dh Open A File
Open disk file with handle
entry AH 3Dh
AL access code byte
(DOS 2.x) bits 0-2 file attribute
000 read only
001 write only
010 read/write
bits 3-7 should be set to zero
(DOS 3.x) bits 0-2 file attribute
000 read only
001 write only
010 read/write
bit 3 reserved
0 should be set to zero
bits 4-6 sharing mode (network)
000 compatibility mode (the way FCBs open files)
001 read/write access denied (exclusive)
010 write access denied
011 read access denied
100 full access permitted
bit 7 inheritance flag
0 file inherited by child process
1 file private to child process
DS:DX address of ASCIIZ pathname string
return flag CF set on error
AX error code
1 error
AX 16 bit file handle
or error code (1, 2, 4, 5, 0Ch)
note 1) Opens any normal, system, or hidden file
2) Files that end in a colon are not opened
3) The rear/write pointer is set at the first byte of the file and the
record size of the file is 1 byte (the read/write pointer can be changed
through function call 42h). The returned file handle must be used for
all subsequent input and output to the file.
4) If the file handle was inherited from a parent process or was
duplicated by DUP or FORCEDUP, all sharing and access restrictions are
also inherited.
5) A file sharing error (error 1) causes an int 24h to execute with an
error code of 2
Function 3Eh Close A File Handle
Close a file and release handle for reuse
entry AH 3Eh
BX file handle
return flag CF 0 successful close
1 error
AX error code if error (6)
note 1) When executed, the file is closed, the directory is updated, and all
buffers for that file are flushed. If the file was changed, the time
and date stamps are changed to current
2) If called with the handle 00000, it will close STDIN (normally the
keyboard).
Function 3Fh Read From A File Or Device
Read from file with handle
entry AH 3Fh
BX file handle
CX number of bytes to read
DS:DX address of buffer
return flag CF 0 successful read
1 error
AX 0 pointer was already at end of file
or number of bytes read
or error code (5, 6)
note 1) This function attempts to transfer the number of bytes specified in CX
to a buffer location. It is not guaranteed that all bytes will be read.
If AX < CX a partial record was read.
2) If performed from STDIN (file handle 0000), the input can be redirected
3) If used to read the keyboard, it will only read to the first CR
4) The file pointer is incremented to the last byte read.
Function 40h Write To A File Or Device
Write to file with handle
entry AH 40h
BX file handle
CX number of bytes to write
DS:DX address of buffer
return flag CF 0 successful write
1 error
AX number of bytes written
or error code (5, 6)
note 1) This call attempts to transfer the number of bytes indicated in CX
from a buffer to a file. If CX and AX do not match after the write,
an error has taken place; however no error code will be returned for
this problem. This is usually caused by a full disk.
2) If the write is performed to STDOUT (handle 0001), it may be redirected
3) To truncate the file at the current position of the file pointer, set
the number of bytes in CX to zero before calling int 21h. The pointer
can be moved to any desired position with function 42h.
4) This function will not write to a file or device marked read-only.
5) May also be used to display strings to CON instead of fn 09h. This
function will write CX bytes and stop; fn 09h will continue to write
until a $ character is found.
6) This is the call that DOS actually uses to write to the screen in DOS
2.x and above.
Function 41h Delete A File From A Specified Subdirectory (UNLINK)
entry AH 41h
DS:DX pointer to ASCIIZ filespec to delete
return CF 0 successful
1 error
AX error code if any (2, 5)
note 1) This function will not work on a file marked read-only
2) Wildcards are not accepted
Function 42h Move a File Read/Write Pointer (LSEEK)
entry AH 42h
AL method code
00h offset from beginning of file
01h offset from present location
02h offset from end of file
BX file handle
CX most significant half of offset
DX least significant half of offset
return AX low offset of new file pointer
DX high offset of new file pointer
CF 0 successful move
1 error
AX error code (1, 6)
note 1) If pointer is at end of file, reflects file size in bytes.
2) The value in DX:AX is the absolute 32 bit byte offset from the beginning
of the file
Function 43h Get/Set file attributes (CHMOD)
entry AH 43h
AL 00h get file attributes
01h set file attributes
CX file attributes to set
bit 0 read only
1 hidden file
2 system file
3 volume label
4 subdirectory
5 written since backup
DS:DX pointer to full ASCIIZ file name
return CF set if error
AX error code (1, 2, 3, 5)
CX file attributes on get
attributes:
01h read only
02h hidden
04h system
0FFh archive
note 1) This call will not change the volume label or directory bits
Function 44h I/O Control for Devices (IOCTL)
Get or Set Device Information
entry AH 44h
AL 00h Get Device Information (from DX)
BX file or device handle
return DX device info
If bit 7 set: (character device)
bit 0: console input device
1: console output device
2: NUL device
3: CLOCK$ device
4: device is special
5: binary (raw) mode
6: not EOF
12: network device (DOS 3.x)
14: can process IOCTL control
strings (func 2-5)
If bit 7 clear: (file)
bits 0-5: block device number
6: file has not been written
12: Network device (DOS 3.x)
15: file is remote (DOS 3.x)
01h Set Device Information (DH must be zero for this call)
DX bits:
0 1 console input device
1 1 console output device
2 1 null device
3 1 clock device
4 1 reserved
5 0 binary mode - don't check for control chars
1 cooked mode - check for control chars
6 0 EOF - End Of File on input
7 device is character device if set, if not, EOF
is 0 if channel has been written, bits 0-5 are
block device number
12 network device
14 1 can process control strings (AL 2-5, can only be
read, cannot be set)
15 n reserved
02h Read CX bytes to device in DS:DX from BX control chan
03h Write Device Control String
BX device handle
CX number of bytes to write
DS:DX pointer to buffer
return AX number of bytes written
04h Read From Block Device (drive number in BL)
BL drive number (0=default)
CX number of bytes to read
DS:DX pointer to buffer
return AX number of bytes read
05h Write to Block Device (drive number in BL)
AX number of bytes transfered
06h Get Input Handle Status
BX file or device handle
return AL 0FFh device ready
00h device not ready
07h Get Output Handle Status
return AL 00h not ready
0FFh ready
note: for DOS 2.x, files are always ready for output
08h Removable Media Bit (DOS 3.x+)
return AX 00h device is removable
01h device is nonremovable
0Fh invalid drive specification
09h Test whether Local or Network Device in BL (DOS 3.x+)
BL drive number (0=default)
return DX attribute word, bit 12 set if device is
remote
0Ah Is Handle in BX Local or Remote? (DOS 3.x+)
BX file handle
return DX (attribute word) bit 15 set if file is remote
0Bh Change Sharing Retry Count to DX (default=3), (DOS 3.x+)
CX delay (default=1)
DX retry count (default=3)
0Ch General IOCTL (DOS 3.3 [3.2?]) allows a device driver to
prepare, select, refresh, and query Code Pages
0Dh Block Device Request (DOS 3.3+)
BL drive number (0=default)
CH major subfunction
CL minor subfunction
40h set device parameters
41h write logical device track
42h format and verify logical device track
60h get device parameters
61h read logical device track
62h verify logical device track
DS:DX pointer to parameter block
0Eh Get Logical Device (DOS 3.3+)
BL drive number (0=default)
return AL=0 block device has only one logical drive
assigned 1..n the last letter used to reference
the device (1=A:,etc)
0Fh Set Logical Device (DOS 3.3+)
BL drive number: 0=default, 1=A:, 2=B:, etc.
BX file handle
CX number of bytes to read or write
DS:DX data or buffer
DX data
return AX number of bytes transferred
or error code (call function 59h for extended error codes)
or status 00h not ready
0FFh ready
CF set if error
Function 45h Duplicate a File Handle (DUP)
entry AH 45h
BX file handle to duplicate
return CF clear AX duplicate handle
set AX error code (4, 6)
note 1) If you move the pointed of one handle, the pointer of the other will
also be moved.
2) The handle in BX must be open
Function 46h Force Duplicate of a Handle (FORCEDUP or CDUP)
Forces handle in CX to refer to the same file at the same
position as BX
entry AH 46h
BX existing file handle
CX new file handle
return CF clear both handles now refer to existing file
set error
AX error code (4, 6)
note 1) If CX was an open file, it is closed first
2) If you move the read/write pointer of either file, both will move
3) The handle in BX must be open
Function 47h Get Current Directory
Places full pathname of current directory/drive into a buffer
entry AH 47h
DL drive (0=default, 1=A:, etc.)
DS:SI points to 64-byte buffer area
return CF clear DS:DI pointer to ASCIIZ pathname of current directory
set AX error code (0Fh)
note String does not begin with a drive identifier or a backslash
Function 48h Allocate Memory
Allocates requested number of 16-byte paragraphs of memory
entry AH 48h
BX number of 16-byte paragraphs desired
return CF clear AX segment address of allocated space
BX maximum number paragraphs available
set AX error code (7, 8)
note BX indicates maximum memory availible only if allocation fails
Function 49h Free Allocated Memory
Frees specified memory blocks
entry AH 49h
ES segment address of area to be freed
return CF clear successful
set AX error code (7, 9)
note 1) This call is only valid when freeing memory obtained by function 48h.
2) A program should not try to release memory not belonging to it.
Function 4Ah Modify Allocated Memory Blocks (SETBLOCK)
Expand or shrink memory for a program
entry AH 4AH
BX new size in 16 byte paragraphs
ES segment address of block to change
return CF clear nothing
set AX error code (7, 8, 9)
or BX max number paragraphs available
note 1) Max number paragraphs availible is returned only if the call fails
2) Memory can be expanded only if there is memory availible
Function 4Bh Load or Execute a Program (EXEC)
entry AH 4Bh
AL 00h load and execute program. A PSP is built for the program
the ctrl-break and terminate addresses are set to the
new PSP.
*01h load but don't execute (note 1)
*01h load but don't execute (internal, DOS 3.x & DESQview)
*02h load but do not execute (internal, DOS 2.x only)
03h load overlay (do not create PSP, do not begin execution)
DS:DX points to the ASCIIZ string with the drive, path, and filename
to be loaded
ES:BX points to a parameter block for the load
(AL=00h) word segment address of environment string to be
passed
dword pointer to the command line to be placed at
PSP+80h
dword pointer to default FCB to be passed at PSP+5Ch
dword pointer to default FCB to be passed at PSP+6Ch
(*AL=01h) word segment of environment (0 = use current)
dword pointer to command line
dword pointer to FCB 1
dword pointer to FCB 2
dword will hold SS:SP on return
dword will hold program entry point (CS:IP) on return
(*AL=02h) word segment of environment (0 = use current)
dword pointer to command line
dword pointer to FCB 1
dword pointer to FCB 2
(AL=03h) word segment address where file will be loaded
word relocation factor to be applied to the image
return CF set error
AX error code (1, 2, 8, 0Ah, 0Bh)
note 1) If you make this call with AL=1 the program will be loaded as if you
made the call with AL=0 except that the program will not be executed.
Additionally, with AL=1 the stack segment and pointer along with the
program's CS:IP entry point are returned to the program which made the
4B01h call. These values are put in the four words at ES:BX+0Eh. On
entry to the call ES:BX points to the environment address, the command
line and the two default FCBs. This form of EXEC is used by DEBUG.COM.
2) Application programs may invoke a secondary copy of the command
processor (normally COMMAND.COM) by using the EXEC function. Your
program may pass a DOS command as a parameter that the secondary
command processor will execute as though it had been entered from the
standard input device.
The procedure is:
A. Assure that adequate free memory (17k for 2.x and 3.0, 23k for 3.1
up) exists to contain the second copy of the command processor and
the command it is to execute. This is accomplished by executing
function call 4Ah to shrink memory allocated to that of your current
requirements. Next, execute function call 48h with BX=0FFFFh. This
returns the amount of memory availible.
B. Build a parameter string for the secondary command processor in the
form:
1 byte length of parameter string
xx bytes parameter string
1 byte 0Dh (carriage return)
For example, the assembly language statement below would build the
string to cause execution of the command FOO.EXE:
DB 19,"/C C:FOO",13
C. Use the EXEC function call (4Bh), function value 0 to cause execution
of the secondary copy of the command processor. (The drive,
directory, and name of the command processor can be gotten from the
COMSPEC variable in the DOS environment passed to you at PSP+2Ch.)
D. Remember to set offset 2 of the EXEC control block to point to the
string built above.
3) All open files of a process are duplicated in the newly created
process after an EXEC, except for files originally opened with the
inheritance bit set to 1.
4) The environment is a copy of the original command processor's
environment. Changes to the EXECed environment are not passed back to
the original. The environment is followed by a copy of the DS:DX
filename passed to the child process. A zero value will cause the
child process to inherit the environment of the calling process. The
segment address of the environment is placed at offset 2Ch of the
PSP of the program being invoked.
5) This function uses the same resident part of COMMAND.COM, but makes a
duplicate of the transient part.
6) How EXEC knows where to return to: Basically the vector for int 22h
holds the terminate address for the current process. When a process
gets started, the previous contents of int 22h get tucked away in the
PSP for that process, then int 22h gets modified. So if Process A
EXECs process B, while Process B is running, the vector for int 22h
holds the address to return to in Process A, while the save location in
Process B's PSP holds the address that process A will return to when
*it* terminates. When Process B terminates by one of the usual legal
means, the contents of int 22h are (surmising) shoved onto the stack,
the old terminate vector contents are copied back to int 22h vector from
Process B's PSP, then a RETF or equivalent is executed to return control
to process A.
7) To load an overlay file with 4B: first, don't de-allocate the memory
that the overlay will load into. With the other 4Bh functions, the
opposite is true--you have to free the memory first, with function 4Ah.
Second, the "segment address where the file will be loaded" (first item
in the parameter block for sub-function 03) should be a paragraph
boundary within your currently-allocated memory. Third, if the
procedures within the overlay are FAR procs (while they execute, CS will
be equal to the segment address of the overlay area), the relocation
factor should be set to zero. On the other hand, if the CS register
will be different from the overlay area's segment address, the
relocation factor should be set to represent the difference. You
determine where in memory the overlay file will load by using the
segment address mentioned above. Overlay files are .EXEs (containing
header, relocation table, and memory image).
8) When function 00h returns, all registers are changed, including the
stack. You must resore SS, SP, and any other required registers.
Function 4Ch Terminate a Process (EXIT)
Quit with ERRORLEVEL exit code
entry AH 4Ch
AL exit code in AL when called, if any, is passed to next process
return none
note 1) Control passes to DOS or calling program
2) return code from AL can be retrieved by ERRORLEVEL or function 4Dh
3) all files opened by this process are closed, buffers are flushed, and
the disk directory is updated
4) Restores Terminate vector from PSP:000Ah
Ctrl-C vector from PSP:000Eh
Critical Error vector from PSP:0012h
Function 4Dh Get Return Code of a Subprocess (WAIT)
Gets return code from functions 31h and 4Dh (ERRORLEVEL)
entry AH 4Dh
return AL exit code of subprogram (functions 31h or 4Ch)
AH circumstance which caused termination
00h normal termination
01h control-break
02h critical device error
03h terminate and stay resident (function 31h)
note The exit code is only returned once
Function 4Eh Find First Matching File (FIND FIRST)
entry AH 4Eh
CX search attributes
DS:DX pointer to ASCIIZ filename (with attributes)
return CF set AX error code (2, 12h)
clear data block written at current DTA
format of block is: (info from BIX)
documented by Micro- |00h 1 byte attribute byte of search
soft as "reserved for |01h 1 byte drive letter for search
DOS' use on subsquent |02h 11 bytes the search name used
Find Next calls" |0Ch 2 bytes word value of last entry
function 4Fh |0Fh 4 bytes dword pointer to this DTA
|13h 2 bytes word directory start
| PC-DOS 3.10 (from INTERRUP.ARC)
|00h 1 byte drive letter
|01h-0Bh bytes search template
|0Ch 1 byte search attributes
| DOS 2.x (and DOS 3.x except 3.1?) (from INTERRUP.ARC)
|00h 1 byte search attributes
|01h 1 byte drive letter
|02h-0Ch bytes search template
|0Dh-0Eh 2 bytes entry count within directory
|0Fh-12h bytes reserved
|13h-14h 2 bytes cluster number of parent directory
15h 1 byte file attribute
16h 2 bytes file time
18h 2 bytes file date
1Ah 2 bytes low word of file size
1Ch 2 bytes high word of file size
1Eh 13 bytes name and extension of file found, plus
1 byte of 0s. All blanks are removed
from the name and extension, and if an
extension is present it is preceded by a
period.
note 1) Will not find volume label
2) This function does not support network operations
3) Wildcards are allowed in the filespec
4) If the attribute is zero, only ordinary files are found. If the volume
label bit is set, only volume labels will be found. Any other attribute
will return that attribute and all normal files together.
5) To look for everything except the volume label, set the hidden, system,
and subdirectory bits all to 1
Function 4Fh Find Next Matching File (FIND NEXT)
Find next ASCIIZ file
entry AH 4Fh
return CF clear data block written at current DTA
set AX error code (2, 12h)
note 1) If file found, DTA is formatted as in call 4Eh
2) Volume label searches using 4Eh/4Fh reportedly aren't 100% reliable
under DOS 2.x. The calls sometime report there's a volume label and
point to a garbage DTA, and if the volume label is the only item they
often won't find it
3) This function does not support network operations
4) Use of this call assumes that the original filespec contained wildcards
Function 50h "Used Internally by DOS" - Set PSP
* Set new Program Segment Prefix (current Process ID)
entry AH 50h
BX segment address of new PSP
return none - swaps PSP's regarded as current by DOS
note 1) By putting the PSP segment value into BX and issuing call 50h DOS stores
that value into a variable and uses that value whenever a file call is
made.
2) Note that in the PSP (or PDB) is a table of 20 (decimal) open file
handles. The table starts at offset 18h into the PSP. If there is an
0FFh in a byte then that handle is not in use. A number in one of the
bytes is an index into an internal FB table for that handle. For
instance the byte at offset 18h is for handle 0, at offset 19h handle
1, etc. up to 13h. If the high bit is set then the file associated by
the handle is not shared by child processes EXEC'd with call 4Bh.
3) Function 50h is dangerous in background operations prior to DOS 3.x as
it uses the wrong stack for saving registers. (same as functions
0..0Ch in DOS 2.x)
4) Under DOS 2.x, this function cannot be invoked inside an int 28h handler
without setting the Critical Error flag
5) Open File information, etc. is stored in the PSP DOS views as current.
If a program (eg. a resident program) creates a need for a second PSP,
then the second PSP should be set as current to make sure DOS closes
that as opposed to the first when the second application finishes.
6) See PC Mag Vol.5, No 9, p.314 for discussion.
7) Used by DOS 3.3 PRINT & DEBUG, DesQview 2.01, Windows 1.03, SYMDEB
from MASM 4.0
Function 51h "Used Internally by DOS" - Get Program Segment Prefix
* Returns the PSP address of currently executing program
entry AH 51h
return BX address of currently executing program
offset
00h program exit point
02h memory size in paragraphs
04h unused (0)
05h CP/M style entry point (far call to DOS)
0Ah terminate address (old int 22h)
0Ch terminate segment
0Eh break address (old int 23h)
10h break segment
12h error address (old int 24h)
14h error segment
16h parent PSP segment
18h DOS 2.0+ open files, 0FFh = unused
2Ch DOS 2.0+ environment segment
2Eh far ptr to process's SS:SP
32h DOS 3.x max open files
34h DOS 3.x openfile table address
36h DOS 3.x openfile table segment
38h unused by DOS versions <= 3.3
50h DOS function dispatcher (FAR routine)
53h unused
55h FCB #1 extension
5Ch FCB #1
6Ch FCB #2
80h command tail / default DTA buffer
note 1) Used in DOS 2.x, 3.x uses 62h
2) Function 51h is dangerous in background operations prior to DOS 3.x as
it uses the wrong stack for saving registers. (same as functions
0..0Ch in DOS 2.x)
3) 50h and 51h might be used if you have more than one process in a PC.
For instance if you have a resident program that needs to open a file
you could first call 51h to save the current id and then call 50h to set
the ID to your PSP.
4) Under DOS 2.x, this function cannot be invoked inside an int 28h handler
without setting the Critical Error flag
5) Used by DOS 3.3 PRINT, DEBUG
Function 52h "Used Internally by DOS" - IN-VARS
* Returns a pointer to a set of DOS data variables MCB chain,
pointer to first device driver and a pointer to disk parameter
blocks (first one)
entry AH 52h
return ES:BX pointer to the DOS list of lists, for disk information. Does not
access the disk, so information in tables might be incorrect if
disk has been changed. Returns a pointer to the following array
of longword pointers:
Bytes Value
-2h,-1h segment of first memory control block
00h-03h pointer to first DOS disk block (see function 36h)
04h-07h Pointer to list of DOS file tables
dword pointer to next file table
word number of files in this table
35h bytes per file
00h-01h number of file handles referring to
this file
02h-06h unknown
07h-0Ah pointer to device driver header if
character device; pointer to DOS Device
Control Block if block device (see
fn 32h for format)
0Bh-1Fh unknown
20h-2Ah filename in FCB format (no path, no
period, blank-padded)
2Bh-2Ch PSP segment of file's owner
2Dh-30h unknown - 0 always
31h-32h unknown
33h-34h unknown
8h-0Bh pointer to CLOCK$ device driver, whether installable or
resident
0Ch-0Fh pointer to actual CON: device driver, whether
installable or resident
(DOS 2.x)
10 number of logical drives in system
11-12 maximum bytes/block of any block device
13-16 unknown
17 beginning (not a pointer. The real beginning!) of NUL
device driver. This is the first device on DOS's linked
list of device drivers.
(DOS 3.x)
10h-11h maximum bytes/block of any block device (0200h)
12h-15h pointer to first disk buffer
16h-19h partially undefined: Pointer to array of drive info:
51h bytes per drive, starting with A: ...
00h-3Fh current path as ASCIIZ, starting with 'x:\'
40h-43h unknown zeros always
44h unknown flags? Usually 40h, except for
entry after last valid entry = 00h
45h-48h pointer to DOS disk block for this drive
49h-4Ah unknown. Current track or block?
-1 if never accessed
4Bh-4Eh unknown -1 always
4Fh-52h unknown 2 always
1Ah-1Dh pointer to FCB table (if CONFIG.SYS contains FCBS=)
1Eh-1Fh size of FCB table
20h number of block devices
21h value of LASTDRIVE command in CONFIG.SYS (default 5)
22h beginning (not a pointer. The real beginning!) of NUL
device driver. This is the first device on DOS's linked
list of device drivers.
note 1) This call is not supported in OS/2 1.0's DOS Compatibility Box
2) Used by DOS 4.0 MEM.EXE, DOS 3.3 ASSIGN.COM, PRINT.COM, SUBST.EXE
3) IMPORTANT: The structure of this list changes with EVERY version of
DOS. It is only partially supported by DR-DOS, and isn't supported
under PC-MOS, OS/2's DOS box, or Wendin-DOS. Since the information
changes so much, I feel it should be put in the "interesting, but
not real useful" category. If you depend on this stuff in production
code, you're going to regret it.
Function 53h "Used Internally by DOS" - Translate BPB
* Translates BPB (BIOS Parameter Block, see below) into a DOS Disk
Block (see function call 32h).
entry AH 53h
DS:SI pointer to BPB
ES:BP pointer to area for DOS Disk Block.
Layout of Disk Block:
bytes value
00h-01h bytes per sector, get from DDB bytes 02h-03h.
02h sectors per cluster, get from (DDB byte 4) + 1
03h-04h reserved sectors, get from DDB bytes 06h-07h
05h number of FATs, get from DDB byte 08h
06h-07h number of root dir entries, get from DDB bytes 09h-0Ah
08h-09h total number of sectors, get from:
((DDB bytes 0Dh-0Eh) - 1) * (sectors per cluster (BPB
byte 2)) + (DDB bytes 0Bh-0Ch)
0Ah media descriptor byte, get from DDB byte 16h
0Bh-0Ch number of sectors per FAT, get from DDB byte 0Fh
return unknown
Function 54h Get Verify Setting
Get verify flag status
entry AH 54h
return AL 00h if flag off
01h if flag on
note Flag can be set with function 2Eh
Function 55h "Used Internally by DOS" - Create "Child" PSP
* Create PSP: similar to function 26h (which creates a new Program
Segment Prefix at segment in DX) except creates a "child" PSP
rather than copying the existing one.
entry AH 55h
DX segment number at which to create new PSP.
return unknown
note 1) This call is similar to call 26h which creates a PSP except that unlike
call 26h the segment address of the parent process is obtained from the
current process ID rather than from the CS value on the stack (from the
INT 21h call). DX has the new PSP value and SI contains the value to be
placed into PSP:2 (top of memory).
2) Function 55 is merely a substitute for function 26h. It will copy the
current PSP to the segment address DX with the addition that SI is
assumed to hold the new memory top segment. This means that function
26h sets SI to the segment found in the current PSP and then calls
function 55h.
Function 56h Rename a File
entry AH 56h
DS:DX pointer to ASCIIZ old pathname
ES:DI pointer to ASCIIZ new pathname
return CF clear successful rename
set AX error code (2, 3, 5, 11h)
note 1) Works with files in same drive only
2) Global characters not allowed in filename
3) The name of a file is its full pathname. The file's full pathname can
be changed, while leaving the actual FILENAME.EXT unchanged. Changing
the pathname allows the file to be "moved" from subdirectory to
subdirectory on a logical drive without actually copying the file.
4) DOS 3.x allows renaming of directories
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
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C H A P T E R F I V E
Interrupts 22h Through 86h
note: the registered version of this chapter is more than twice this size.
Interrupt 22h Terminate Address
(0:0088h)
This interrupt transfers control to the far (dword) address at this interrupt
location when an application program terminates. The default address for this
interrupt is 0:0088h through 0:008Bh. This address is copied into the program's
Program Segment Prefix at bytes 0Ah through 0Dh at the time the segment is
created and is restored from the PSP when the program terminates. The calling
program is normally COMMAND.COM or an application. Do not issue this interrupt
directly, as the EXEC function call does this for you. If an application
spawns a child process, it must set the Terminate Address prior to issuing the
EXEC function call, otherwise when the second program terminated it would
return to the calling program's Terminate Address rather than its own. This
address may be set with int 21, function 25h.
Interrupt 23h Ctrl-Break Exit Address
(0:008Ch)
If the user enters a Ctrl-Break during STDIN, STDOUT, STDPRN, or STDAUX, int
23h is executed. If BREAK is on, int 23h is checked on MOST function calls
(notably 06h). If the user written Ctrl-Break routine saves all registers, it
may end with a return-from-interrupt instruction (IRET) to continue program
execution. If the user-written interrupt program returns with a long return, the
carry flag is used to determine whether the program will be aborted. If the
carry flag is set, the program is aborted, otherwise execution continues (as
with a return by IRET). If the user-written Ctrl-Break interrupt uses function
calls 09h or 0Ah, (Display String or Buffered Keyboard Input) then a three-byte
string of 03h-0Dh-0Ah (ETX/CR/LF) is sent to STDOUT. If execution is continued
with an IRET, I/O continues from the start of the line. When the interrupt
occurs, all registers are set to the value they had when the original function
call to DOS was made. There are no restrictions on what the Ctrl-Break handler
is allowed to do, including DOS function calls, as long as the registers are
unchanged if an IRET is used. If the program creates a new segment and loads a
second program which itself changes the Ctrl-Break address, the termination of
the second program and return to the first causes the Ctrl-Break address to
be restored from the PSP to the value it had before execution of the second
program.
Interrupt 24h Critical Error Handler
(0:0090h)
When a critical error occurs within DOS, control is transferred to an error
handler with an int 24h. This may be the standard DOS error handler (ABORT,
RETRY, IGNORE) or a user-written routine.
On entry to the error handler, AH will have its bit 7=0 (high order bit)
if the error was a disk error (probably the most common error), bit 7=1 if
not.
BP:SI contains the address of a Device Header Control Block from which
additional information can be retrieved (see below).
The register is set up for a retry operation and an error code is in the
lower half of the DI register with the upper half undefined. These are the
error codes:
The user stack is in effect and contains the following from top to bottom:
IP DOS registers from issuing int 24h
CS int 24h
flags
AX user registers at time of signal
BX int 21h request
CX
DX
SI
DI
BP
DS
ES
IP from original int 21h
CS
flags
To reroute the critical error handler to a user-writen critical error handler,
the following should be done:
Before an int 24h occurs:
1) The user application initialization code should save the int 24h vector and
replace the vector with one pointing to the user error routine.
When the int 24h occurs:
2) When the user error routine received control it should push the flag
registers onto the stack and execute a far call to the original int 24h
vector saved in step 1.
3) DOS gives the appropriate prompt, and waits for user input (Abort, Retry,
Ignore, Fail). After the user input, DOS returns control to the user error
routine instruction following the far call.
4) The user error routine can now do any tasks nescessary. To return to the
original application at the point the error occurred, the error routine needs
to execute an IRET instruction. Otherwise, the user error routine should
remove the IP, CS, and flag registers from the stack. Control can then be
passed to the desired point.
Int 24h provides the following values in registers on entry to the interrupt
handler:
entry AH status byte (bits)
7 0 disk I/O hard error
1 other error - if block device, bad FAT
- if char device, code in DI
6 unused
5 0 if IGNORE is not allowed
1 if IGNORE is allowed
4 0 if RETRY is not allowed
1 if RETRY is allowed
3 0 if FAIL is not allowed
1 if FAIL is allowed
2 \ disk area of error 00 = DOS area 01 = FAT
1 / 10 = root dir 11 = data area
0 0 if read operation
1 if write operation
AL drive number if AH bit 7 = 1, otherwise undefined
If it is as hard error on disk (AH bit 7=0), register AL
contains the failing drive number (0=A:, 1=B:, etc.).
BP:SI address of a Device Header Control Block for which error
occurred block device if high bit of BP:SI+4 = 1
low byte of DI: error code (note: high byte is undefined)
error code description
00h attempt to write on write-protected diskette
01h unknown unit
02h drive not ready
03h unknown command
04h data error (bad CRC)
05h bad request structure length
06h seek error
07h unknown media type
08h sector not found
09h printer out of paper
0Ah write fault
0Bh read fault
0Ch general failure
0Fh invalid disk change (DOS 3.x+)
10h (DOS 3.x) FCB unavailable
11h (DOS 3.x) sharing buffer overflow
The handler must return this information:
The registers are set such that if an IRET is executed, DOS responds according
to (AL) as follows:
AL 00h ignore the error
01h retry the operation
02h terminate via int 22h
03h fail the system call that is in progress (DOS 3.x+)
note 1) Be careful when choosing to ignore a response because this causes DOS to
beleive that an operation has completed successfully when it may not
have.
2) If the error was a character device, the contents of AL are invalid.
OTHER ERRORS
If AH bit 7=1, the error occurred on a character device, or was the result of
a bad memory image of the FAT. The device header passed in BP:SI can be examined
to determine which case exists. If the attribute byte high-order bit indicates
a block device, then the error was a bad FAT. Otherwise, the error is on a
character device.
If a character device is involved, the contents of AL are unpredictable, the
error code is in DI as above.
Notes:
1. Before giving this routine control for disk errors, DOS performs several
retries. The number of retries varies according to the DOS version.
2. For disk errors, this exit is taken only for errors occurring during an
int 21h function call. It is not used for errors during an int 25h or 26h.
3. This routine is entered in a disabled state.
4. All registers must be preserved.
5. This interrupt handler should refrain from using DOS function calls. If
necessary, it may use calls 01h through 12h. Use of any other call destroys
the DOS stack and leaves DOS in an unpredictable state.
6. The interrupt handler must not change the contents of the device header.
7. If the interrupt handler handles errors itself rather than returning to DOS,
it should restore the application program's registers from the stack,
remove all but the last three words on the stack, then issue an IRET. This
will return to the program immediately after the int 21h that experienced
the error. Note that if this is done DOS will be in an unstable state until
a function call higher than 12h is issued, therefore not recommended.
8. For DOS 3.x, IGNORE requests (AL=0) are converted to FAIL for critical
errors that occur on FAT or DIR sectors.
9. For DOS 3.10 up, IGNORE requests (AL=0) are converted to FAIL requests
for network critical errors (50-79).
The device header pointed to by BP:SI is as follows:
DWORD Pointer to next device (0FFFFh if last device)
WORD Attributes:
Bit 15 1 if character device.
If bit 15 is 1:
Bit 0 = 1 if current standard input
Bit 1 = 1 if current standard output
Bit 2 = 1 if current NULL device
Bit 3 = 1 if current CLOCK device
0 if block device
Bit 14 is the IOCTL bit
WORD pointer to device driver strategy entry point
WORD pointer to device driver interrupt entry point
8-BYTE character device named field for block devices. The first byte is the
number of units.
To tell if the error occurred on a block or character device, look at bit 15
in the attribute field (WORD at BP:SI+4).
If the name of the character device is desired, look at the eight bytes
starting at BP:SI+10.
HANDLING OF INVALID RESPONSES (DOS 3.x)
A) If IGNORE (AL=0) is specified by the user and IGNORE is not allowed
(bit 5=0), make the response FAIL (AL=3).
B) If RETRY (AL=1) is specified by the user and RETRY is not allowed
(bit 4=0), make the response FAIL (AL=3).
C) If FAIL (AL=3) is specified by the user and FAIL is not allowed (bit
3=0), make the response ABORT. (AL=2)
Interrupt 25h Absolute Disk Read
Interrupt 26h Absolute Disk Write
(0:0094h, 0:0098h)
These transfer control directly to the device driver. On return, the original
flags are still on the stack (put there by the INT instruction). This is
necessary because return information is passed back in the current flags.
The number of sectors specified is transferred between the given drive and the
transfer address. Logical sector numbers are obtained by numbering each sector
sequentially starting from track 0, head 0, sector 1 (logical sector 0) and
continuing along the same head, then to the next head until the last sector on
the last head of the track is counted. Thus, logical sector 1 is track 0, head
0, sector 2; logical sector 2 is track 0, head 0, sector 3; and so on. Numbering
then continues wih sector 1 on head 0 of the next track. Note that although the
sectors are sequentially numbered (for example, sectors 2 and 3 on track 0 in
the example above), they may not be physically adjacent on disk, due to
interleaving. Note that the mapping is different from that used by DOS 1.10 for
dual-sided diskettes.
The request is as follows:
int 25 for Absolute Disk Read,
int 26 for Absolute Disk Write
entry AL drive number (0=A:, 1=B:, etc)
CX number of sectors to read
DS:BX disk transfer address (buffer)
DX first relative sector to read - beginning logical sector number
return CF set if error
AL error code issued to int 24h in low half of DI
AH 01h bad command
02h bad address mark
03h write-protected disk
04h requested sector not found
08h DMA failure
10h data error (bad CRC)
20h controller failed
40h seek operation failed
80h attachment failed to respond
note 1) Original flags on stack! Be sure to pop the stack to prevent
uncontrolled growth
2) Ints 25 and 26 will try rereading a disk if they get an error the first
time.
3) All registers except the segment registers are destroyed by these calls
Interrupt 25h ABSOLUTE DISK READ
(except DOS 4.0/Compaq DOS 3.31 >32M partition)
entry AL drive number (0=A, 1=B, etc)
DS:BX pointer to Disk Transfer Address (buffer)
CX number of sectors to read
DX first relative sector to read
return CF 1 if error
AL error code issued to int 24h in low half of DI
AH 80h attachment failed to respond
40h seek operation failed
20h controller failed
10h data error (bad CRC)
08h DMA failure
04h requested sector not found
03h write-protected disk
02h bad address mark
01h bad command
note Original flags on stack!
Interrupt 25h DOS 4.0/Compaq DOS 3.31 - ABSOLUTE DISK READ
(>32M hard-disk partition)
entry AL drive number (0=A, 1=B, etc)
CX 0FFFFh
DS:BX Packet address
DWORD sector number
WORD number of sectors to read
DWORD transfer address
return same as above?
note Partition is potentially >32Mb (and requires this form of the call) if
bit 1 of device attribute word in device driver is set
Interrupt 26h ABSOLUTE DISK WRITE
(except DOS 4.0/Compaq DOS 3.31 >32M partition)
entry AL drive number (0=A, 1=B, etc)
DS:BX pointer to Disk Transfer Address (buffer)
CX number of sectors to write
DX first relative sector to write
return CF 1 if error
AL error code issued to int 24h in low half of DI
AH same error codes as for int 25h
note Original flags on stack!
Interrupt 26h DOS 4.0/Compaq DOS 3.31 - ABSOLUTE DISK WRITE
(>32M hard disk partitions)
entry AL drive number (0=A, 1=B, etc)
CX 0FFFFh
DS:BX Packet address
DWORD sector number
WORD number of sectors to write
DWORD transfer address
return same as above?
note Partition is potentially >32M (and requires this form of the call) if
bit 1 of device attribute word in device driver is set
Interrupt 27h Terminate And Stay Resident
(0:009Ch) (obsolete)
This vector is used by programs that are to remain resident when COMMAND.COM
regains control.
After initializing itself, the program must set DX to its last address plus
one relative to the program's initial DS or ES value (the offset at which other
programs can be loaded), then execute interrupt 27h. DOS then considers the
program as an extension of itself, so the program is not overlaid when other
programs are executed. This is useful for loading programs such as utilities
and interrupt handlers that must remain resident.
entry CS current program segment
DX last program byte + 1
return none
note 1) This interrupt must not be used by .EXE programs that are loaded into
the high end of memory.
2) This interrupt restores the interrupt 22h, 23h, and 24h vectors in the
same manner as interrupt 20h. Therefore, it cannot be used to install
permanently resident Ctrl-Break or critical error handler routines.
3) The maximum size of memory that can be made resident by this method is
64K.
4) Memory can be more efficiently used if the block containing a copy of
the environment is deallocated before terminating. This can be done by
loading ES with the segment contained in 2Ch of the PSP, and issuing
function call 49h (Free Allocated Memory).
5) DOS function call 4Ch allows a program to pass a completion code to DOS,
which can be interpreted with processing (see function call 31h).
6) Terminate and stay resident programs do not close files.
7) Int 21, function 31h is the preferred method to cause a program to
remain resident because this allows return information to be passed and
allows a program larger than 64K to remain resident.
Interrupt 28h (not documented by Microsoft)
* DOS Idle Interrupt
Int 28h has been provided by DOS since release 2.0. The int 28h process is
similar to the "Timer Tick" process provided by BIOS via int 1Ch in that it is
an "outbound" (from DOS) call which an application can "hook onto" to get
service at a particular entry point. DOS normally only issues int 28h when it
recieves a function call (int 21h) from a foreground application with an
argument in the range of 0 thru 12 (0Ch) in the AH register, or when it is
idling waiting for keyboard input. In effect, when DOS issues int 28h, it is
saying to the background task "I'm not doing anything hot right now, if you can
use the time, go ahead." This means that a foreground application which doesn't
do many low-number DOS functions can preempt CPU time easily.
It is possible, if you are careful, to enhance the background priority by
providing more int 28h calls than DOS normally would issue.
When int 28h is being issued it is usually safe to do DOS calls. You won't get
int 28hs if a program is running that doesn't do its keyboard input through
DOS. You should rely on the timer interrupt for these.
It is used primarily by the PRINT.COM routines, but any number of other
routines can be chained to it by saving the original vector and calling it with
a FAR call (or just JMPing to it) at the end of the new routine.
Int 28h is not called at all when any non-trivial foreground task is running.
As soon as a foreground program has a file open, int 28h no longer gets called.
Could make a good driver for for a background program that works as long as
there is nothing else going on in the machine.
DOS uses 3 separate internal stacks: one for calls 01h through 0Ch; another
for calls 0Dh and above; and a third for calls 01h through 0Ch when a Critical
Error is in progress. When int 28h is called, any calls above 0Ch can be
executed without destroying the internal stack used by DOS at the time.
The byte which is pushed on the stack before an int 28h just indicates which
stack area is being used by the current int 21h call. In DOS 3.1, the code
sequence that calls int 28h looks like this:
PUSH SS:[0304]
INT 28
POP SS:[0304]
The low-order byte of the word pushed contains 1 if the int 21h call currently
in progress is for services 1 through 0Ch, and 0 for service 0 and for 0Dh and
up. Assuming that the last DOS call was not a reentrant one, this tells you
which set of DOS services should be safe to call.
If the InDOS flag is zero on int 28h, then it was called by someone other than
DOS, and the word on the stack should NOT be examined.
entry no parameters availible
return none
note 1) The int 28h handler may invoke any int 21h function except functions
00h through 0Ch (and 50h/51h under DOS 2.x unless DOS CritErr flag is
set).
2) Apparently int 28h is also called during screen writes
3) Until some program installs its own routine, this interrupt vector
simply points to an IRET opcode.
4) Supported in OS/2 1.0's DOS Compatibility Box
Interrupt 29h (not documented by Microsoft)
* Internal - Quick Screen Output
This method is extremely fast (much faster than DOS 21h subfunctions 2 and 9,
for example), and it is portable, even to "non-compatible" MS-DOS computers.
entry AL character to output to screen
return unknown
note 1) Documented by Digital Research's DOS Reference as provided with the
DEC Rainbow
2) If ANSI.SYS is installed, character output is filtered through it.
3) Works on the IBM PC and compatibles, Wang PC, HP-150 and Vectra, DEC
Rainbow, NEC APC, Texas Instruments PC and others
4) This interrupt is called from the DOS's output routines if output is
going to a device rather than a file, and the device driver's attribute
word has bit 3 (04h) set to "1".
5) This call has been tested with MSDOS 2.11, PCDOS 2.1, PCDOS 3.1, PCDOS
3.2, and PCDOS 3.3.
6) Used in IBMBIO.COM as a vector to int 10, function 0Eh (write TTY)
followed by an IRET.
Interrupt 2Ah Microsoft Networks - Session Layer Interrupt
* (not documented by Microsoft)
entry AH 00h check to see if network BIOS installed
return AH <> 0 if installed
01h execute NETBIOS request
02h set net printer mode
03h get shared-device status (check direct I/O)
AL 00h
DS:SI pointer to ASCIIZ disk device name
return CF 0 if allowed
04h execute NETBIOS
AL 0 for error retry
1 for no retry
ES:BX pointer to network control block
return AX 0 for no error
AH 1 if error
AL error code
05h get network resource information
AL 00h
return AX reserved
BX number of network names
CX number of commands
DX number of sessions
06h Network Print-stream Control
note NETBIOS 1.10
20h unknown
note AL=01h intercepted by DESQview 2.0
80h Begin DOS Critical Section
AL 1 to 6
81h End DOS Critical Section
AL 1 to 6
82h Server Hook
return unknown
note called by the int 21h function dispatcher
in DOS 3.10+ for function 0 and functions
greater than 0Ch except 59h
84h keyboard busy loop
note similar to DOS's int 28h
Interrupt 2Bh (not documented by Microsoft)
* Unknown - Internal Routine for DOS (IRET)
Interrupt 2Ch (not documented by Microsoft)
* Unknown - Internal Routine for DOS (IRET)
Interrupt 2Dh (not documented by Microsoft)
* Unknown - Internal Routine for DOS (IRET)
Interrupt 2Eh (undocumented by Microsoft) (DOS 2.0+)
* Internal Routine for DOS (Alternate EXEC)
This interrupt passes a command line addressed by DS:SI to COMMAND.COM. The
command line must be formatted just like the unformatted parameter area of a
Program Segment Prefix. That is, the first byte must be a count of characters,
and the second and subsequent bytes must be a command line with parameters,
terminated by a carriage return character.
When executed, int 2Eh will reload the transient part of the command
interpreter if it is not currently in memory. If called from a program that
was called from a batch file, it will abort the batch file. If executed from a
program which has been spawned by the EXEC function, it will abort the whole
chain and probably lock up the computer. Int 2Eh also destroys all registers
including the stack pointer.
Int 2Eh is called from the transient portion of the program to reset the DOS
PSP pointers using the above Functions #81 & #80, and then reenters the
resident program.
When called with a valid command line, the command will be carried out by
COMMAND.COM just as though you had typed it in at the DOS prompt. Note that the
count does not include the carriage return. This is an elegant way to perform a
SET from an application program against the master environment block for
example.
entry DS:SI pointer to an ASCIIZ command line in the form:
count byte
ASCII string
carriage return
null byte
note 1) Destroys all registers including stack pointer
2) Seems to work OK in both DOS 2.x and 3.x
3) It is reportedly not used by DOS.
4) As far as known, int 2Eh is not used by DOS 3.1, although it was called
by COMMAND.COM of PCDOS 3.0, so it appears to be in 3.1 only for the
sake of compatibility.
Interrupt 2Fh Multiplex Interrupt
Interrupt 2Fh is the multiplex interrupt. A general interface is defined
between two processes. It is up to the specific application using interrupt
2Fh to define specific functions and parameters.
This interrupt is becoming more commonly used as the availible interrupt 21
functions are getting to be in short supply. Int 2Fh doesn't require any
support from DOS itself for it to be used in application programs. It's not
handled by DOS, but by the programs themselves.
Every multiplex interrupt handler is assigned a specific multiplex number.
The multiplex number is specified in the AH register; the AH value tells which
program your request is directed toward. The specific function that the handler
is to perform is placed in the AL register. Other parameters are places in the
other registers as needed. The handlers are chained into the 2Fh interrupt
vector and the multiplex number is checked to see if any other application is
using the same multiplex number. There is no predefined method for assigning a
multiplex number to a handler. You must just pick one. To avoid a conflict if
two applications choose the same multiplex number, the multiplex numbers used by
an application should be patchable. In order to check for a previous
installation of the current application, you can search memory for a unique
string included in your program. If the value you wanted in AH is taken but
you don't find the string, then another application has grabbed that location.
Int 2Fh was not documented under DOS 2.x. There is no reason not to use int 2Fh
as the multiplex interrupt in DOS 2.x. The only problem is that DOS 2.x does not
initialize the int 2Fh vector, so when you try to chain to it like you are
supposed to, it will crash. If your program checks the vector for being zero
and initializes it itself or doesn't chain in that case, it will work for you
n 2.x just the same as 3.x.
Function 01h PRINT.COM
Register AH identifies which program is to handle the interrupt.
Values 00h-7Fh are reserved for DOS, not that anyone cares much.
Values 0C0h-0FFh are reserved for applications.
Register AL contains the function code if used
entry AH 01h
AL 00h PRINT Get Installed State
This call must be defined by all int 2Fh handlers. It
is used by the caller of the handler to determine if
the handler is present. On entry, AL=0. On return, AL
contains the installed state as follows:
return AL 0FFh installed
01h not installed, not OK to install
00h not installed, OK to install
01h PRINT Submit File
DS:DX pointer to submit packet
format byte level
dword pointer to ASCIIZ filename
return CF set if error
AX error code
note 1) A submit packet contains the level (BYTE) and a pointer
to the ASCIIZ string (DWORD in offset:segment form).
The ASCIIZ string must contain the drive, path, and
filename of the file you want to print. The filename
cannot contain global filename characters.
return CF set if error
AX error code
02h PRINT Cancel File
On entry, AL=2 and DS:DX points to the ASCIIZ string for
the print file you want to cancel. Global filename
characters are allowed in the filename.
DS:DX pointer to ASCIIZ file name to cancel (wildcards OK)
return CF set if error
AX error code
03h PRINT remove all files
return CF set if error
AX error code
04h PRINT hold queue/get status
This call holds the jobs in the print queue so that you
can scan the queue. Issuing any other code releases the
jobs. On entry, AL=4. On return, DX contains the error
count. DS:SI points to the print queue. The print queue
consists of a series of filename entries. Each entry is
64 bytes long. The first entry in the queue is the file
currently being printed. The end of the queue is marked
by the entry having a null as the first character.
return DX error count
DS:SI pointer to print queue (null-string terminated
list of 64-byte ASCIIZ filenames)
CF set if error
AX error code
01h function invalid
02h file not found
03h path not found
04h too many open files
05h access denied
08h queue full
09h spooler busy
0Ch name too long
0Fh drive invalid
05h PRINT restart queue
return CF set if error
AX error code
Function 05h DOS 3.x critical error handler
entry AH 05h
AL 00h installation check
return AL 00h not installed, OK to install
01h not installed, can't install
0FFh installed
note This set of functions allows a user program to
partially or completely override the default
critical error handler in COMMAND.COM
AL 01h handle error - nonzero error code in AL
return CF clear
ES:DI pointer to ASCIIZ error message
CF set use default error handler
AL (?)
Function 06h ASSIGN
entry AH 06h
00h installation check
return AH <> 0 if installed
01h get memory segment
return ES segment of ASSIGN work area
Function 10h SHARE
entry AH 10h
AL 00h installation check
return AL 00h not installed, OK to install
01h not installed, not OK to install
0FFh installed
Function 11h Multiplex - network redirection
entry AH 11h
AL 00h installation check
return AL 00h not installed, OK to install
01h not installed, not OK to install
0FFh installed
01h-05h unknown
06h close remote file
07h-09h unknown
0Ah unknown
stack word (?)
return CF set on error
0Bh unknown
stack word (?)
return CF set on error(?)
0Ch unknown
0Dh unknown
0Eh unknown
stack word (?)
return (?)
0Fh-16h unknown
17h unknown
stack word (?)
return (?)
18h unknown
stack word (?)
return (?)
19h-1Dh unknown
1Eh do redirection
stack word function to execute
return CF set on error
1Fh printer setup
stack word function(?)
return CF set on error(?)
20h-25h unknown
stack word (?)
26h unknown
Function 12h multiplex, DOS 3.x internal services
entry AH 12h
AL 00h installation check
return AL 0FFh for compatibility with other
int 2Fh functions
01h close file (?)
stack word value - unknown
return BX unknown
CX unknown
ES:DI pointer to unknown value
note Can be called only from within DOS
02h get interrupt address
stack word vector number
return ES:BX pointer to interrupt vector
stack unchanged
03h get DOS data segment
return DS segment of IBMDOS.COM file
04h normalize path separator
stack word character to normalize
return AL normalized character (forward slash
turned to backslash)
stack unchanged
05h output character
stack word character to output
return stack unchanged
note Can be called only from within DOS
06h invoke critical error
return AL 0-3 for Abort, Retry, Ignore, Fail
note Can be called only from within DOS
07h move disk buffer (?)
DS:DI pointer to disk buffer
return buffer moved to end of buffer list
note Can be called only from within DOS
08h decrement word
ES:DI pointer to word to decrement
return AX new value of word
note Word pointed to by ES:DI decremented,
skipping zero
09h unknown
DS:DI pointer to disk buffer(?)
return (?)
note Can be called only from within DOS
0Ah unknown
note Can be called only from within DOS
0Bh unknown
ES:DI pointer to system file table entry(?)
return AX (?)
note Can be called only from within DOS
0Ch unknown
note Can be called only from within DOS
0Dh get date and time
return AX current date in packed format
DX current time in packed format
note Can be called only from within DOS
0Eh do something to all disk buffers (?)
return DS:DI pointer to first disk buffer
note can be called only from within DOS
0Fh unknown
DS:DI pointer to (?)
return DS:DI pointer to (?)
note 1) Can be called only from within DOS
2) Calls on function 1207h
10h find dirty/clean(?) buffer
DS:DI pointer to first disk buffer
return DS:DI pointer to first disk buffer which has
(?) flag clear
ZF clear if found
set if not found
11h normalize ASCIIZ filename
DS:SI pointer to ASCIIZ filename to normalize
ES:DI pointer to buffer for normalized filename
return destination buffer filled with uppercase
filename, with slashes turned to backslashes
12h get length of ASCIIZ string
ES:DI pointer to ASCIIZ string
return CX length of string
13h uppercase character
stack word character to convert to uppercase
return AL uppercase character
stack unchanged
14h compare far pointers
DS:SI first pointer
ES:DI second pointer
return ZF set if pointers are equal
ZF clear if not equal
15h unknown
DS:DI pointer to disk buffer
stack word (?)
return stack unchanged
note Can be called only from within DOS
16h get address of system FCB
BX system file table entry number
return ES:DI pointer to system file table entry
17h set default drive (?)
stack word drive (0=A:, 1=B:, etc)
return DS:SI pointer to drive data block for
specified drive
stack unchanged
note Can be called only from within DOS
18h get something (?)
return DS:SI pointer to (?)
19h unknown
stack word drive (0=default, 1=A:, etc)
return (?)
stack unchanged
note 1) Can be called only from within DOS
2) Calls function 1217h
1Ah get file's drive
DS:SI pointer to filename
return AL drive
(0=default, 1=A:, etc, 0FFh=invalid)
1Bh set something (?)
CL unknown
return AL (?)
note Can be called only from within DOS
1Ch checksum memory
DS:SI pointer to start of memory to checksum
CX number of bytes
DX initial checksum
return DX checksum
note Can be called only from within DOS
1Dh unknown
DS:SI pointer to (?)
CX (?)
DX (?)
return AX (?)
CX (?)
DX (?)
1Eh compare filenames
DS:SI pointer to first ASCIIZ filename
ES:DI pointer to second ASCIIZ filename
return ZF set if filenames equivalent
clear if not
1Fh build drive info block
stack word drive letter
return ES:DI pointer to drive info block
(will be overwritten by next call)
stack unchanged
note Can be called only from within DOS
20h get system file table number
BX file handle
return CF set on error, error code in AL
AL 06h (invalid file handle)
CF clear if successful
byte ES:[DI] = system file table entry
number for file handle
21h unknown
DS:SI pointer to (?)
return (?)
note Can be called only from within DOS
22h unknown
SS:SI pointer to (?)
return nothing(?)
note Can be called only from within DOS
23h check if character device (?)
return DS:SI pointer to device driver with
same name as (?)
note Can be called only from within DOS
24h delay
return after delay of (?) ms
note Can be called only from within DOS
25h get length of ASCIIZ string
DS:SI pointer to ASCIIZ string
return CX length of string
Function 43h Microsoft Extended Memory Specification (XMS)
Function 5453h TesSeRact Standard for Ram-Resident Program Communication
Function 64h SCRNSAV2.COM
entry AH 64h
AL 00h installation check
return AL 00h not installed
0FFh installed
note SCRNSAV2.COM is a screen saver for PS/2's with VGA by Alan Ballard
Function 7Ah Novell NetWare
entry AH 7Ah
AL 00h installation check
note 1) Returns address of entry point for IPX and SPX
2) Parameters are listed under int 21
Function 087h APPEND
entry AH 087h
AL 00h APPEND installation check
return AH <> 0 if installed
01h APPEND - unknown
02h APPEND - version check
Function 088h Microsoft Networks
entry AH 088h
AL 00h network program installation check
return AH <> 0 if installed
BX installed component flags (test in this order!)
bit 6 server
bit 2 messenger
bit 7 receiver
bit 3 redirector
01h unknown
02h unknown
03h get current POST address
return ES:BX POST address
04h set new POST address
ES:BX new POST address
09h network version check
Function 0AAh VIDCLOCK.COM
entry AH 0AAh
AL 00h installation check
return AL 00h not installed
0FFh installed
note VIDCLOCK.COM is a memory-resident clock by Thomas G. Hanlin III
Function 0BBh Network Functions
entry AH 0BBh
AL 00h net command installation check
01h, 02h unknown
03h get server POST address
04h get server POST address
Function 0F7h AUTOPARK.COM (PD TSR hard disk parking utility)
entry AH 0F7h
AL 00h installation check
return AL 00h not installed
0FFh installed
note AUTOPARK is a TSR HD parker by Alan D. Jones
01h set parking delay
BX:CX 32 bit count of 55ms timer ticks
MSDOS 2Fh functions 01h (PRINT), 02h (ASSIGN), 10h (SHARE):
return AX Error
Codes Description
01h invalid function number
02h file not found
03h path not found
04h too many open files
05h access denied
06h invalid handle
08h queue full
09h busy
0Ch name too long
0Fh invalid drive was specified
CF clear (0) if OK
set (1) if error - error returned in AX
note 1) The multiplex numbers AH=0h through AH=7Fh are reserved for DOS.
Applications should use multiplex numbers 80h through 0FFh.
2) When in the chain for int 2Fh, if your code calls DOS or if you execute
with interrupts enabled, your code must be reentrant/recursive.
3) Important! In versions of DOS prior to 3.0, the int 2Fh vector was
initialized to zero rather than being pointed into the DOS service area.
You must initialize this vector manually under DOS 2.x.
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� Miscellaneous Interrupts - in numerical order �
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Interrupt 30h (not a vector!) far jump instruction for CP/M-style calls
Interrupt 31h Unknown
note The CALL 5 entry point does a FAR jump to here
Interrupt 32h Unknown
Interrupt 33h Used by Microsoft Mouse Driver
Function Calls
Function Requests
00h Reset Driver and Read Status
entry AH 00h
return AH status
0 hardware/driver not installed
-1 hardware/driver installed
BX number of buttons
-1 two buttons
0 other than two
3 Mouse Systems mouse
01h Show Mouse Cursor
entry AH 01h
return unknown
02h Hide Mouse Cursor
entry AH 02h
return unknown
note multiple calls to hide the cursor will require multiple calls
to function 01h to unhide it.
03h Return Position and Button Status
entry AH 03h
return BX button status
bit 0 left button pressed if 1
bit 1 right button pressed if 1
bit 2 middle button pressed if 1 (Mouse Systems mouse)
CX column
DX row
04h Position Mouse Cursor
entry AH 04h
CX column
DX row
return unknown
05h Return Button Press Data
entry AH 05h
BX button
0 left
1 right
2 middle (Mouse Systems mouse)
return AH button states
bit 0 left button pressed if 1
bit 1 right button pressed if 1
bit 2 middle button pressed if 1 (Mouse Systems mouse)
BX no. of times specified button pressed since last call
CX column at time specified button was last pressed
DX row at time specified button was last pressed
06h Return Button Release Data
entry AH 06h
BX button
0 left
1 right
2 middle (Mouse Systems mouse)
return AH button states
bit 0 left button pressed if 1
bit 1 right button pressed if 1
bit 2 middle button pressed if 1 (Mouse Systems mouse)
BX no. of times specified button released since last call
CX column at time specified button was last released
DX row at time specified button was last released
07h Define Horizontal Cursor Range
entry AH 0007h
CX minimum column
DX maximum column
return unknown
08h Define Vertical Cursor Range
entry AH 08h
CX minimum row
DX maximum row
return unknown
09h Define Graphics Cursor
entry AH 09h
BX column of cursor hot spot in bitmap (-16 to 16)
CX row of cursor hot spot (-16 to 16)
ES:DX pointer to bitmap
16 words screen mask
16 words cursor mask
return unknown
note Each word defines the sixteen pixels of a row, low bit
rightmost
0Ah Define Text Cursor
entry AH 0Ah
BX hardware/software text cursor
00h software
CX screen mask
DX cursor mask
01h hardware
CX start scan line
DX end scan line
return unknown
note When the software cursor is selected, the char/attribute data
at the current screen position is ANDed with the screen mask
and the with the cursor mask
0Bh Read Motion Counters
entry AH 0Bh
return CX number of mickeys mouse moved horiz. since last call
DX number of mickeys mouse moved vertically
note 1) A mickey is the smallest increment the mouse can sense.
Positive values indicate up/right
0Ch Define Interrupt Subroutine Parameters
entry AH 0Ch
CX call mask bit
bit 0 call if mouse moves
bit 1 call if left button pressed
bit 2 call if left button released
bit 3 call if right button pressed
bit 4 call if right button released
bit 5 call if middle button pressed (Mouse Systems)
bit 6 call if middle button released (Mouse Systems)
ES:DX address of FAR routine
return unknown
note when the subroutine is called, it is passed these values:
AH condition mask (same bit assignments as call mask)
BX button state
CX cursor column
DX cursor row
DI horizontal mickey count
SI vertical mickey count
0Dh Light Pen Emulation On
entry AH 0Dh
return unknown
0Eh Light Pen Emulation Off
entry AH 0Eh
return unknown
0Fh Define Mickey/Pixel Ratio
entry AH 0Fh
CX number of mickeys per 8 pixels horizontally
DX number of mickeys per 8 pixels vertically
return unknown
10h Define Screen Region for Updating
entry AH 10h
CX,DX X,Y coordinates of upper left corner
SI,DI X,Y coordinates of lower right corner
return unknown
note Mouse cursor is hidden during updating, and needs to be
explicitly turned on again
11h not documented by Microsoft
12h Set Large Graphics Cursor Block
AH 12h
BH cursor width in words
CH rows in cursor
BL horizontal hot spot (-16 to 16)
CL vertical hot spot (-16 to 16)
ES:DX pointer to bit map of screen and cursor maps
return AH -1 if successful
note PC Mouse. Not documented by Microsoft
13h Define Double-Speed Threshold
entry AH 13h
DX threshold speed in mickeys/second,
0 = default of 64/second
return unknown
note If speed exceeds threshold, the cursor's on-screen motion
is doubled
14h Exchange Interrupt Subroutines
entry AH 14h
return unknown
15h Return Drive Storage Requirements
entry AH 15h
return BX size of buffer needed to store driver state
16h Save Driver State
entry AH 16h
ES:DX pointer to buffer
return unknown
17h Restore Driver State
entry AH 17h
ES:DX pointer to buffer containing saved state
return unknown
18h-1Ch not documented by Microsoft; unknown
1Dh Define Display Page Number
entry AH 1Dh
1Eh Return Display Page Number
entry AH 1Eh
return unknown
42h PCMouse - Get MSmouse Storage Requirements
AH 42h
return AX 0FFFFh successful
BX buffer size in bytes for functions 50h and 52h
00h MSmouse not installed
42h functions 42h, 50h, and 52h not supported
52h PCMouse - Save MSmouse State
entry AH 50h
BX buffer size
ES:DX pointer to buffer
return AX 0FFFFh if successful
52h PCMouse - restore MSmouse state
entry AH 52h
BX buffer size
ES:DX pointer to buffer
return AX 0FFFFh if successful
Int 33: In addition, the following functions are appended to BIOS int 10h and
implemented as the EGA Register Interface Library:
0F0h read one register
0F1h write one register
0F2h read consecutive register range
0F3h write consecutive register range
0F4h read non-consecutive register set
0F5h write non-consecutive register set
0F6h revert to default register values
0F7h define default register values
0FAh get driver status
Interrupt 34h Turbo C/Microsoft languages - Floating Point emulation
This interrupt emulates opcode 0D8h
Interrupt 35h Turbo C/Microsoft languages - Floating Point emulation
This interrupt emulates opcode 0D9h
Interrupt 36h Turbo C/Microsoft languages - Floating Point emulation
This interrupt emulates opcode 0DAh
Interrupt 37h Turbo C/Microsoft languages - Floating Point emulation
This interrupt emulates opcode 0DBh
Interrupt 38h Turbo C/Microsoft languages - Floating Point emulation
This interrupt emulates opcode 0DCh
Interrupt 39h Turbo C/Microsoft languages - Floating Point emulation
This interrupt emulates opcode 0DDh
Interrupt 3Ah Turbo C/Microsoft languages - Floating Point emulation
This interrupt emulates opcode 0DEh
Interrupt 3Bh Turbo C/Microsoft languages - Floating Point emulation
This interrupt emulates opcode 0DFh
Interrupt 3Ch Turbo C/Microsoft languages - Floating Point emulation
This int emulates instructions with an ES segment override
Interrupt 3Dh Turbo C/Microsoft languages - Floating Point emulation
This interrupt emulates a standalone FWAIT instruction
Interrupt 3Eh Turbo C/Microsoft languages - Floating Point emulation
Interrupt 3Fh Overlay manager interrupt (Microsoft LINK.EXE)
Default overlay interrupt; may be changed with LINK switch
Interrupt 40h Hard Disk BIOS
Pointer to disk BIOS entry when a hard disk controller is
installed. The BIOS routines use int 30h to revector the
diskette handler (original int 13h) here so int 40 may be used
for hard disk control
Interrupt 41h Hard Disk Parameters (XT,AT,XT2,XT286,PS except ESDI disks)
Pointer to first Hard Disk Parameter Block, normally located
in the controller card's ROM. This table may be copied to RAM
and changed, and this pointer revectored to the new table.
note 1) format of parameter table is:
dw cylinders
db heads
dw starting reduced write current cylinder (XT only, 0 for others)
db maximum ECC burst length
db control byte
bits 0-2 drive option (XT only, 0 for others)
bit 3 set if more than 8 heads
bit 4 always 0
bit 5 set if manufacturer's defect map on max cylinder+1
bit 6 disable ECC retries
bit 7 disable access retries
db standard timeout (XT only, 0 for others)
db formatting timeout (XT only, 0 for others)
db timeout for checking drive (XT only, 0 for others)
dw landing zone (AT, PS/2)
db sectors/track (AT, PS/2)
db 0
2) normally vectored to ROM table when system is initialized.
Interrupt 42h Pointer to screen BIOS entry (EGA, VGA, PS/2)
Relocated (by EGA, etc.) video handler (original int 10h).
Revectors int 10 calls to EGA BIOS.
Interrupt 43h Pointer to EGA graphics character table. The POST initializes
this vector pointing to the default table located in the EGA
ROM BIOS. (PC-2 and up). Not initialized if EGA not present.
This vector was referred to (mistakenly) as the Video
Parameters table in the original EGA BIOS listings.
Interrupt 44h Pointer to graphics character table. This table contains the
(0:0110h) dot patterns for the first 128 characters in video modes 4,5,
and 6, and all 256 characters in all additional graphics modes.
Not initialized if EGA not present.
2) EGA/VGA/CONV/PS - EGA/PCjr fonts, characters 00h to 7Fh
3) Novell NetWare - High-Level Language API
4) This interrupt is not used by some EGA cards.
Interrupt 45h Reserved by IBM (not initialized)
Interrupt 46h Pointer to second hard disk, parameter block (AT, XT/286, PS/2)
(see int 41h) (except ESDI hard disks) (not initialized unless
specific user software calls for it)
Interrupt 47h Reserved by IBM (not initialized)
Interrupt 48h Cordless Keyboard Translation (PCjr, XT [never delivered])
(0:0120h) This vector points to code to translate the cordless keyboard
scancodes into normal 83-key values. The translated scancodes
are then passed to int 9. (not initialized on PC or AT)
Interrupt 49h Non-keyboard Scan Code Translation Table Address (PCjr)
(0:0124h) This interrupt is used for operation of non-keyboard devices
on the PCjr, such as the Keystronic Numeric Keypad.
This interrupt has the address of a table used to translate
non-keyboard scancodes (greater than 85 excepting 255). This
interrupt can be revectored by a user application. IBM
recommends that the default table be stored at the beginning
of an application that required revectoring this interrupt,
and that the default table be restored when the application
terminates. (not initialized on PC or AT)
The PCjr BIOS can interpret scancodes other than those
generated by the keyboard to allow for expansion. The keyboard
generates scancodes from 01h to 055h, including 0FFh. Any
scancodes above 55h (56h through 7Eh for make codes and 0D6h
through 0FEh for break codes) are processed in the following
manner:
1) if the incoming make code falls within the range of the
translate table whose address is pointed to by int 49h, it
is translated into the corresponding scancode. Any incoming
break codes above 0D5h are ignored.
2) if the new translated scancode ius less and 56h, it is
processed by the BIOS as a keyboard scancode and the same
data is placed in the BIOS keyboard buffer.
3) if the translated scancode is higher than 55h or the
incoming scancode is outside the range of the translate
table, 40h is added creating a new extended scancode. The
extended scancode is placed in the BIOS keyboard buffer with
the character code of 00h (NUL). This utilitizes the range
of 96h through 0BEh for scancodes 56h through 7Eh.
The default translate-table maps scancodes 56h through 6Ah to
existing keyboard values. Codes 6Bh theough 0BEh are mapped (by
adding 40h) to extended codes 0ABh through 0FEh since they are
outside the range of the default translate table.
The format of the translate table is:
0 length - the number of nonkeyboard scancodes that are
mapped within the table (from 1 to n)
1 to n word high byte 00h (NUL) byte scancode with low order
byte representing the scancode mapped values relative
to their input values within the range of 56h through
7Eh
With this layout, all keyboard scancodes can be intercepted
through int 9h and and nonkeyboard scancodes can be intercepted
through int 48h.
Interrupt 4Ah Real-Time Clock Alarm (Convertible, PS/2)
(not initialized on PC or AT)
Invoked by BIOS when real-time clock alarm occurs
Interrupt 4Bh Reserved by IBM (not initialized)
Interrupt 4Ch Reserved by IBM (not initialized)
Interrupt 4Dh Reserved by IBM (not initialized)
Interrupt 4Eh Reserved by IBM (not initialized)
Used instead of int 13h for disk I/O on TI Professional PC
Interrupt 4Fh Reserved by IBM (not initialized)
Interrupt 50-57 IRQ0-IRQ7 relocated by DesQview
(normally not initialized)
Interrupt 58h Reserved by IBM (not initialized)
Interrupt 59h Reserved by IBM (not initialized)
GSS Computer Graphics Interface (GSS*CGI)
DS:DX Pointer to block of 5 array pointers
return CF 0
AX return code
CF 1
AX error code
note 1) Int 59 is the means by which GSS*CGI language bindings
communicate with GSS*CGI device drivers and the GSS*CGI
device driver controller.
2) Also used by the IBM Graphic Development Toolkit
Interrupt 5Ah Reserved by IBM (not initialized)
Interrupt 5Bh Reserved by IBM (not initialized)
Interrupt 5Ah Cluster Adapter BIOS entry address
(normally not initialized)
Interrupt 5Bh Reserved by IBM (not initialized) (cluster adapter?)
Interrupt 5Ch NETBIOS interface entry port
ES:BX pointer to network control block
return AL error code (0 if none)
note 1) When the NETBIOS is installed, interrupts 13 and 17 are interrupted by
the NETBIOS; interrupt 18 is moved to int 86 and one of int 2 or 3 is
used by NETBIOS. Also, NETBIOS extends the int 15 function 90 and 91h
functions (scheduler functions)
2) Normally not initialized.
3) TOPS network card uses DMA 1, 3 or none.
Interrupt 5Dh Reserved by IBM (not initialized)
Interrupt 5Eh Reserved by IBM (not initialized)
Interrupt 5Fh Reserved by IBM (not initialized)
Interrupt 60h-67h User Program Interrupts (availible for general use)
Various major programs make standardized use of this group
of interrupts. Details of common use follows
Interrupt 60h 10-Net Network
entry AH 11h Lock and Wait
AL drive number or 0
DX number of seconds to wait
ES:SI Ethernet address or 0
DS:BX pointer to 31-byte ASCIIZ semaphore name
return AL status
0 successful
1 timeout
2 server not responding
3 invalid semaphore name
4 semaphore list is full
5 invalid drive ID
6 invalid Ethernet address
7 not logged in
8 write to network failed
9 semaphore already logged for this CPU
entry AH 12h Lock
AL drive number or 0 for default
ES:SI Ethernet address or 0
DS:BX pointer to 31-byte ASCIIZ semaphore name
return AL status (see function 11h)
1 semaphore currently logged
note Unlike function 11h, this function returns immediately
entry AH 13h Unlock
AL drive number or 0
ES:SI Ethernet address or 0
DS:BX pointer to 31-byte ASCIIZ semaphore name
return AL status (see function 11h)
1 semaphore not logged
Interrupt 67h Used by Lotus-Intel-Microsoft Expanded Memory Specification
user and Ashton-Tate/Quadram/AST Enhanced Expanded Memory
specification (See Chapter 10)
Interrupt 68h Not Used (not initialized)
Interrupt 69h Not Used (not initialized)
Interrupt 6Ah Not Used (not initialized)
Interrupt 6Bh Not Used (not initialized)
Interrupt 6Ch System Resume Vector (Convertible) (not initialized on PC)
DOS 3.2 Realtime Clock update
Interrupt 6Dh Not Used (not initialized)
Interrupt 6Eh Not Used (not initialized)
Interrupt 6Fh Novell NetWare - PCOX API (3270 PC terminal interface)
Interrupt 6Fh 10-Net Network API
entry AH 00h Login
DS:DX login record
8 bytes user name
8 bytes password
12 bytes name of super-station
return CL security level
AX status
0000h good login
0FF01h no response from superstation
0FF02h network error
0FF03h invalid password
0FF04h no local buffer
0FF05h superstation not available
0FF06h node already logged in
0FF07h login not valid from this node
0FF08h node ID already in use
01h Logoff
return CX number of files closed
AX status
0000h successful
0FF08h superstation ID not already logged in
02h Status of node
DS:DX pointer to 512-byte record
8 bytes user name (0 if none)
byte station type
0 workstation
1 superstation
4 logged into multiple superstations
24 bytes list of superstations logged into more than one
superstation
12 bytes node ID
word message count for this station (send for user
node, receive for superstations)
for superstations only:
word drives allocated (bit 0=A:, bit 1=B:,...)
byte user service flag
bit 4: SUBMIT is on
3: mail waiting for node
2: calendar waiting for you
1: news waiting for you
0: mail waiting for you
byte printers allocated (bit 0=LPT1,...)
byte number of unprinted spool files
byte number of opened files
byte number of logged on files
byte primary drive (1=A:)
byte reserved
n bytes list of logged on node IDs (each 12 bytes, max
38 IDs)
return CF set on error
AX error code
0FF01h no response from node
0FF02h network error
0FF04h no local buffer
0FF16h invalid node ID
03h Get Address of Configuration Table
return ES:BX pointer to record (actually starts at [BX-25])
word count of dropped Send6F
word buffer start address
word comm driver base address
word send/receive retry count
byte number of 550ms loops
word UFH address
word CDIR address
word LTAB address
word SFH address
word FTAB address
word RLTAB address
word SMI address
word NTAB address
ES:BX pointer to word address of first CT_DRV
byte number of DRV entries
8 bytes login name
12 bytes node ID
6 bytes node address
byte flag
byte CT_CFLG
bit 1: sound bell
bit 0: CHAT permit
byte CT_PSFLG
bit 5: PRINT permit
bit 4: KB initiated
bit 3: CHAT called FOXPTRM
bit 2: SUBMIT active
bit 1: SUBMIT received
bit 0: SUBMIT permit
byte reserved
word receive message count
word send message count
word retry count
word failed count
word driver errors
word dropped responses/CHATs
9 bytes list ID/NTAB address (3 entries-LPT1-3?)
6 bytes AUX ID/NTAB address (2 entries-COM1-2?)
byte active CB channel
byte received 6F messages on queue
9 bytes activity counters for channels 1-9
04h Send
DS:BX pointer to record
12 bytes receiving node's ID
word length of data at DX
DS:DX pointer to data (max 1024 bytes)
return CF set on error
AX error code
0FF01h timeout
0FF02h network error
0FF04h no local buffer
0FF16h invalid parameter (bad length)
05h Receive
CX number of seconds before timeout
DS:DX pointer to receive buffer
12 bytes sending node's ID
word length of message
n bytes message (maximum 1024 bytes)
return CF set on error
AX error code
0FF01h timeout
0FF18h sent message has been dropped
06h Unknown
07h Lock Handle
BX file handle
CX:DX starting offset in file
SI record length
return CF set on error
AX error code
0FF01h timeout
02h file not found
0FF17h record locked by another user
08h Unlock Handle
BX file handle
AL mode
0 unlock all
1 unlock record at CX:DX
return CF set on error
AX error code
02h file not found
0Bh Lock Semaphore, Return Immediately
AL drive number or 0
ES:SI Ethernet address or 0
DS:BX pointer to 31-byte ASCIIZ semaphore name
return AL status
0 successful
1 semaphore currently locked
2 server not responding
3 invalid semaphore name
4 semaphore list is full
5 invalid drive ID
6 invalid Ethernet address
7 not logged in
8 write to network failed
9 semaphore already logged in this CPU
0Ch unlock semaphore
AL drive number or 0
ES:SI Ethernet address or 0
DS:BX pointer to 31-byte ASCIIZ semaphore name
return AL status (see AH=0Bh)
1 semaphore not locked
0Dh Who
CX length of data
DS:DX pointer to array of records to be filled
12 bytes node ID
byte flag (1=workstation, 2=superstation)
return CL number of records returned (responding stations)
0Eh spool/print
DS:DX pointer to record
word 0 initiate spool
1 abort print
2 close spool
3 delete spool
4 print
5 get report info
11 bytes file name
byte notification
bit 6: do ID page
bit 5: no form feed
bit 3: notify at print completion
bit 2: notify at print start and reply?
bit 1: notify at print start
bit 0: no notification
byte days to keep (0FFh=forever)
byte device (1=LPT1)
word length of following data area
n bytes $SCNT records returned if code in first word
is 05h
return CF set on error
AX error code
0FF16h invalid parameter
0FF17h device not mounted
0FF18h already spooling to named device
11h Lock FCB
AL mode
0 sequential
1 random
2 random block
DS:DX pointer to FCB
return CF set on error
AX 02h file not found
0FF01h timeout
0FF17h record locked by another user
12h Unlock FCB
AL mode
0 sequential
1 random
2 random block
DS:DX pointer to FCB
return CF set on error
AX 02h file not found
Interrupt 70h IRQ 8, Real Time Clock Interrupt (AT, XT/286, PS/2)
Interrupt 71h IRQ 9, Redirected to IRQ 8 (AT, XT/286, PS/2)
LAN Adapter 1 (rerouted to int 0Ah [IRQ2] by BIOS)
Interrupt 72h IRQ 10 (AT, XT/286, PS/2) Reserved
Interrupt 73h IRQ 11 (AT, XT/286, PS/2) Reserved
Interrupt 74h IRQ 12 Mouse Interrupt (PS/2)
Interrupt 75h IRQ 13, Coprocessor Error, BIOS Redirect to int 2 (NMI) (AT)
Interrupt 76h IRQ 14, Hard Disk Controller (AT, XT/286, PS/2)
Interrupt 77h IRQ 15 (AT, XT/286, PS/2) Reserved
Interrupt 78h Not Used
Interrupt 79h Not Used
Interrupt 7Ah Novell NetWare - LOW-LEVEL API
Interrupt 7Bh-7Eh Not Used
Interrupt 7Fh unknown
Used by second copy of COMMAND set with SHELL=
Not used by COMMAND /C at DOS prompt
Interrupt 80h-85h Reserved by BASIC
note interrupts 80h through ECh are apparently unused and not initialized.
Interrupt 86h Relocated by NETBIOS int 18
Interrupt 86h-0F0h Used by BASIC when BASIC interpreter is running
Intrerrupt 0E0h CP/M-86 function calls
Interrupt 0E4h Logitech Modula-2 v2.0 MONITOR
entry AX 05h monitor entry
06h monitor exit
BX priority
Interrupt 0F0h unknown
Used by secondary copy of COMMAND when SHELL= set
Not used by COMMAND /C at DOS prompt
Interrupts 0F1h-0FFh (absolute addresses 3C4-3FF)
Location of Interprocess Communications Area
Interrupt 0F8h Set Shell Interrupt (OEM)
Set OEM handler for int 21h calls from 0F9h through 0FFh
entry AH 0F8h
DS:DX pointer to handler for Functions 0F9h thru 0FFh
note 1) To reset these calls, pass DS and DX with 0FFFFh. DOS is set up to
allow ONE handler for all 7 of these calls. Any call to these handlers
will result in the carry bit being set and AX will contain 1 if they are
not initialized. The handling routine is passed all registers just as
the user set them. The OEM handler routine should be exited through an
IRET.
2) 10 ms interval timer (Tandy?)
Interrupt 0F9h First of 8 SHELL service codes, reserved for OEM shell (WINDOW);
use like HP Vectra user interface?
Interrupt 0FAh USART ready (RS-232C)
Interrupt 0FBh USART RS ready (keyboard)
Interrupt 0FCh Unknown
Interrupt 0FDh reserved for user interrupt
Interrupt 0FEh AT/XT286/PS50+ - destroyed by return from protected mode
Interrupt 0FFh AT/XT286/PS50+ - destroyed by return from protected mode
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
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ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
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C H A P T E R S I X
DOS CONTROL BLOCKS AND WORK AREAS
Contrary to popular belief, DOS is not limited to 640k of work space. This
constraint is enforced by the mapping of ROM and video RAM into the default 1
megabyte CPU address space. Some MSDOS compatible machines, such as the Sanyo
55x series, can have as much as 768k of contiguous DOS workspace with the
appropriate option boards. Since DOS has no real memory management, it cannot
deal with a fragmented workspace. Fragmented RAM (such as RAM mapped into the
option ROM address space) can be dealt with as a RAMdisk or other storage area
by using a device driver or other software.
The 80386 CPU and appropriate control software can create a DOS workspace of
more than one megabyte. Certain add-on boards can also add more than a
megabyte of workspace, but only for specially written software. Since these
are all proprietary schemes, little information is availible at present.
When DOS loads a program, it first sets aside a section of memory for the
program called the program segment, or code segment. Then it constructs a
control block called the program segment prefix, or PSP, in the first 256
(100h) bytes. Usually, the program is loaded directly after the PSP at 100h.
The PSP contains various information used by DOS to help run the program.
The PSP is always located at offset 0 within the code segment. When a program
recieves control certain registers are set to point to the PSP. For a COM
file, all registers are set to point to the beginning of the PSP and the
program begins at 100h. For the more complex EXE file structures, only DS and
ES registers are set to point to the PSP. The linker passes the settings for
the DS, IP, SS, and SP registers and may set the starting location in CS:IP to
a location other than 100h.
IBMBIO provides an IRET instruction at absolute address 847h for use as a
dummy routine for interrupts that are not used by DOS. This lets the interrupts
do nothing until their vectors are rerouted to their appropriate handlers.
A storage block is used by DOS to record the amount and location of allocated
memory within the machine's address space.
A storage block, a Program Segment Prefix, and an environment area are built
by DOS for each program currently resident in the address space. The storage
block is used by DOS to record the address range of memory allocated to a
program. It is used by DOS to find the next availible area to load a program
and to determine if there is enough memory to run that porogram. When a
memory area is in use, it is said to be allocated. Then the program ends, or
releases memory, it is said to be deallocated.
A storage block contains a pointer to the Program Segment Prefix associated
with each program. This control block is constructed by IBMDOS for the purpose
of providing standardized areas for DOS/program communication. Within the
PSP are areas which are used to save interrupt vectors, pass parameters to
the program, record disk directory information, and to buffer disk reads and
writes. This control block is 100h bytes in length and is followed by the
program module loaded by DOS.
The PSP contains a pointer to the environment area for that program. This
area contains a copy of the current DOS SET, PROMPT, COMSPEC, and PATH values
as well as any user-set variables. The program may examine and modify this
information as desired.
Each storage block is 10h bytes long, although only 5 bytes are currently
used by DOS. The first byte contains 4Dh (a capital M) to indicate that it
contains a pointer to the next storage block. A 5Ah (a capital Z) in the
first byte of a storage block indicatres there are no more storage blocks
following this one (it is the end of the chain). The identifier byte is
followed by a 2 byte segment number for the associated PSP for that program.
The next 2 bytes contain the number of segments what are allocated to the
program. If this is not the last storage block, then another storage block
follows the allocated memory area.
When the storage block contains zero for the number of allocated segments,
then no storage is allocated to this block and the next storage block
immediately follows this one. This can happen when memory is allocated and
then deallocated repeatedly.
IBMDOS constructs a storage block and PSP before loading the command
interpreter (default is COMMAND.COM).
If the copy of COMMAND.COM is a secondary copy, it will lack an environment
address at PSP+2Ch.
THE DISK TRANSFER AREA (DTA)쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
DOS uses an area in memory to contain the data for all file reads and writes
that are performed with FCB function calls. This are is known as the disk
transfer area. This disk transfer area (DTA) is sometimes called a buffer.
It can be located anywhere in the data area of your application program and
should be set by your program.
Only one DTA can be in effect at a time, so your program must tell DOS what
memory location to use before using any disk read or write functions. Use
function call 1Ah (Set Disk Transfer Address) to set the disk transfer address.
Use function call 2Fh (Get Disk Transfer Address) to get the disk transfer
address. Once set, DOS continues to use that area for all disk operations until
another function call 1Ah is issued to define a new DTA. When a program is given
control by COMMAND.COM, a default DTA large enough to hold 128 bytes is
established at 80h into the program's Program Segment Prefix.
For file reads and writes that are performed with the extended function calls,
there is no need to set a DTA address. Instead, specify a buffer address when
you issue the read or write call.
DOS PROGRAM SEGMENT쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
When you enter an external command or call a program through the EXEC function
call, DOS determines the lowest availible address space to use as the start of
available memory for the program being started. This area is called the Program
Segment.
At offset 0 within the program segment, DOS builds the Program Segment Prefix
control block. EXEC loads the program after the Program Segment Prefix (at
offset 100h) and gives it control.
The program returns from EXEC by a jump to offset 0 in the Program Segment
Prefix, by issuing an int 20h, or by issuing an int 21h with register AH=00h or
4Ch, or by calling location 50h in the PSP with AH=00h or 4Ch.
It is the responsibility of all programs to ensure that the CS register
contains the segment address of the Program Segment Prefix when terminating by
any of these methods except call 4Ch.
All of these methods result in returning to the program that issued the EXEC.
During this returning process, interrupt vectors 22h, 23h, and 24h (Terminate,
Ctrl-Break, and Critical Error Exit addresses) are restored from the values
saved in the PSP of the terminating program. Control is then given to the
terminate address.
When a program receives control, the following conditions are in effect:
For all programs:
1) The segment address of the passed environment is contained at offset 2Ch in
the Program Segment Prefix.
2) The environment is a series of ASCII strings totalling less than 32k bytes
in the form: NAME=value The default environment is 160 bytes.
Each string is a maximum of 127 bytes terminated by a byte of zeroes for a
total of 128 bytes, and the entire set of strings is terminated by another
byte of zeroes. Following the byte of zeroes that terminates the set of
environment string is a set of initial arguments passed to a program that
contains a word count followed by an ASCIIZ string. The ASCIIZ string
contains the drive, path, and filename.ext of the executable program.
Programs may use this area to determine where the program was loaded from.
The environment built by the command processor (and passed to all programs
it invokes) contains a COMSPEC=string at a minimum (the parameter on COMSPEC
is the path used by DOS to locate COMMAND.COM on disk). The last PATH and
PROMPT commands issued will also be in the environment, along with any
environment strings entered through the SET command.
The environment that you are passed is actually a copy of the invoking
process's environment. If your application terminates and stays resident
through int 27h, you should be aware that the copy of the environment passed
to you is static. That is, it will not change even if subsequent PATH,
PROMPT, or SET commands are issued.
The size of the environment may be changed from its default of 160 bytes
by using the SHELL= command in the config.sys from in DOS version 3.1 up,
or COMMAND.COM may be patched in earlier versions.
The environment can be used to transfer information between processes or to
store strings for later use by application programs. The environment is
always located on a paragraph boundary. This is its format:
byte ASCIIZ string 1
byte ASCIIZ string 2
....
byte ASCIIZ string n
byte of zeros (0)
Typically the environment strings have the form:
NAME = VALUE
The length of NAME or VALUE can be anything desired as long as it still fits
into the 123 byte space (4 bytes are used by "SET ").
Following the byte of zeros in the environment, a WORD indicates the number
of other strings following.
If the environment is part of an EXECed command interpreter, it is followed
by a copy of the DS:DX filename passed to the child process. A zero value
causes the newly created process to inherit the parent's environment.
3) Offset 80h in the PSP contains code to invoke the DOS function dispatcher.
Thus, by placing the desired function number in AH, a program can issue a
long call to PSP+50h to invoke a DOS function rather than issuing an int 21h.
4) The disk transfer address (DTA) is set to 80h (default DTA in PSP).
5) File Control Blocks 5Ch and 6Ch are formatted from the first two parameters
entered when the command was invoked. Note that if either parameter contained
a path name, then the corresponding FCB will contain only a valid drive
number. The filename field will not be valid.
6) An unformatted parameter area at 81h contains all the characters entered
after the command name (including leading and imbedded delimiters), with 80h
set to the number of characters. If the <, >, or | parameters were entered
on the command line, they (and the filenames associated with them) will not
appear in this area, because redirection of standard input and output is
transparent to applications.
(For EXE files only)
7) DS and ES registers are set to point to the PSP.
8) CS, IP, SS, and SP registers are set to the values passed by the linker.
(For COM files only)
9) For COM files, offset 6 (one word) contains the number of bytes availible in
the segment.
10) Register AX reflects the validity of drive specifiers entered with the
first two parameters as follows:
AL=0FFh is the first parameter contained an invalid drive specifier,
otherwise AL=00h.
AL=0FFh if the second parameter contained an invalid drive specifier,
otherwise AL=00h.
11) All four segment registers contain the segment address of the inital
allocation block, that starts within the PSP control block. All of user
memory is allocated to the program. If the program needs to invoke another
program through the EXEC function call (4Bh), it must first free some memory
through the SETBLOCK function call to provide space for the program being
invoked.
12) The Instruction Pointer (IP) is set to 100h.
13) The SP register is set to the end of the program's segment. The segment size
at offset 6 is rounded down to the paragraph size.
14) A word of zeroes is placed on top of the stack.
The PSP (with offsets in hexadecimal) is formatted as follows:
(* = undocumented)
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커
� P R O G R A M S E G M E N T P R E F I X �
쳐컴컴컴쩡컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� offset� size � C O N T E N T S �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0000h � 2 bytes � int 20h �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0002h � 2 bytes � segment address, end of allocation block �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0004h � 1 byte � reserved, normally 0 �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0005h � 5 bytes � FAR call to MSDOS function dispatcher (int 21h) �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 000Ah � 4 bytes � previous termination handler interrupt vector (int 22h) �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 000Eh � 4 bytes � previous contents of ctrl-C interrupt vector (int 23h) �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0012h � 4 bytes � prev. critical error handler interrupt vector (int 24h) �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0016h � 22 bytes � reserved for DOS �
읕컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
* � 2 bytes � (16) parent process' PSP �
* � 20 bytes � (18) "handle table" used for redirection of files �
旼컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 002Ch � 2 bytes � segment address of the program's environment block �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 002Eh � 34 bytes � reserved, DOS work area �
읕컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
* � 4 bytes � (2E) stores the calling process's stack pointer when �
� � switching to DOS's internal stack. �
* � � (32) DOS 3.x max open files �
* � 2 bytes � (3A) size of handle table |these functions are in here �
* � 4 bytes � (3C) handle table address |but reported addresses vary �
旼컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0050h � 3 bytes � int 21h, RETF instruction �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0053h � 2 bytes � reserved - unused? �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0055h � 7 bytes � reserved, or FCB#1 extension �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 005Ch � 16 bytes � default unopened File Control Block #1 �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 006Ch � 16 bytes � default unopened FCB #2 (overlaid if FCB #1 opened) �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0080h � 1 byte � parameter length (number of chars entered after filename) �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0081h � ... � parameters �
쳐컴컴컴탠컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 00FFh � 128 bytes� command tail and default Disk Transfer Area (DTA) �
읕컴컴컴좔컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
1. The first segment of availible memory is in segment (paragraph) form. For
example, 1000h would respresent 64k.
2. Offset 2Ch contains the segment address of the environment.
3. Programs must not alter any part of the PSP below offset 5Ch.
PSP (comments):
offset 00h contains hex bytes CD 20, the int 20h opcode. A program can end
by making a jump to this location when the CS points to the PSP.
For normal cases, int 21, function 4Ch should be used.
offset 02h contains the segment-paragraph address of the end of memory as
reported by DOS. (which may not be the same as the real end of RAM).
Multiply this number by 10h or 16 to get the amount of memory
availible. ex. 1000h would be 64k.
offset 04h "reserved or used by DOS" according to Microsoft
offset 05h contains a long call to the DOS function dispatcher. Programs may
jump to this address instead of calling int 21 if they wish.
Used by Basic and other CPM object-code translated programs. It is
slower than standard int 21h.
offset 0Ah, 0Eh, 12h
vectors (IP, CS)
offset 16h PSP:16h is the segment address of the invoking program's PSP, which
* will most often be COMMAND.COM but perhaps may be a secondary
non-permanent COMMAND or a multitasking shell, etc. At any rate,
the resident shell version of COMMAND.COM has PSP:16H = PSP, which
indicates "don't look any lower in memory" for the command
interpreter. To find the beginning of the allocation chain, look
backwards through the PSP link addresses until the link address is
equal to the PSP segment address that it resides in. This should
be COMMAND.COM. To find COMMAND.COM's environment, look at the word
stored at offset 0BD3h (PC-DOS 3.1 only). This is a segment
address, so look there at offset 0.
18h handle alias table (networking). Also you can make PRN go to CON,
* CON go to PRN, ERR go to PRN, etc. 0FFh = availible.
offset 2Ch is the segment:offset address of the environment for the program
using this particular PSP. This pointer does not point to
COMMAND.COM's environment unless it is a second copy of COMMAND.
offset 2Eh the DWORD at PSP+2Eh is used by DOS to store the calling process's
* stack pointer when switching to DOS's own private stack - at the end
of a DOS function call, SS:SP is restored from this address.
32h, 34h
* table of number of file handles (to 64k of handles!)
offset 40h 2 byte field points to the segment address of COMMAND.COM's PSP in
* "weird" EXE files produced by Digital Research RASMPC/LINKPC.
EXE files created with these tools can cause all sorts of problems
with standard MSDOS debugging tools.
offset 50h contains a long call to the DOS int 21 function dispatcher.
offset 5Ch, 65h, 6Ch
contain FCB information for use with FCB function calls. The first
FCB may overlay the second if it is an extended call; your program
should revector these areas to a safe place if you intend to use
them.
offset 5Ch 16 bytes first command-line argument (formatted as uppercase 11
character filename)
offset 6Ch 16 bytes second command-line argument (formatted as uppercase 11
character filename)
offset 7Ch-7Fh
"reserved or used by DOS"
offset 80h 1 byte number of bytes in command line argument
offset 80h, 81h
contain the length and value of parameters passed on the command
line.
offset 81h 97 bytes unformatted command line and/or default DTA
offset 0FFh contains the DTA
The PSP is created by DOS for all programs and contains most of the information
you need to know about a program running. You can change the environment for
the current process, however, but for the parent process, DOS in this case, you
need to literally backtrack to DOS or COMMAND.COM's PSP. In order to get there
you must look at the current PSP. At offset 16h of the current PSP segment,
there a 2 byte segment address to the parent or previous process PSP.
From there you can manipulate the enviroment by looking at offset 2Ch. As you
know, at offset 2Ch, there is 2 byte segment address to the environment block.
Try this under debug and explore the addresses located at these offsets;
offset length description
------------------------------------------------------------
16h 2 segment address of parent process PSP
2Ch 2 segment address of environment block.
Remember under debug you will have to backtrack two times.
Programs Parent
--------------------------
command.com none
debug.com command.com
program debug.com
MEMORY CONTROL BLOCKS쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
DOS keeps track of allocated and availible memory blocks, and provides four
function calls for application programs to communicate their memory needs to
DOS. These calls are:
48h --- allocate memory (MALLOC)
49h --- free allocated memory
4Ah --- modify allocated memory blocks (SETBLOCK)
4Bh --- load or execute program (EXEC)
DOS manages memory as follows:
DOS build a control block for each block of memory, whether free or allocated.
For example, if a program issues an "allocate" (48h), DOS locates a block of
free memory that satisfies the request, and then "carves" the requested memory
out of that block. The requesting program is passed the location of the first
byte of the block that was allocated for it - a memory management control block,
describing the allocated block, has been built for the allocated block and a
second memory management control block describes the amount of space left in the
original free block of memory. When you do a SETBLOCK to shrink an allocated
block, DOS builds a memory management control block for the area being freed and
adds it to the chain of control blocks. Thus, any program that changed memory
that is not allocated to it stands a chance of destroying a DOS memory
management control block. This causes unpredictable results that don't show up
until an activity is performed where DOS uses its chain of control blocks. The
normal result is a memory allocation error, which means a system reset will be
required.
When a program (command or application program) is to be loaded, DOS uses the
EXEC function call 4Bh to perform the loading.
This is the same function call that is availible to applications programs for
loading other programs. This function call has two options:
Function 00h, to load and execute a program (this is what the command
processor uses to load and execute external commands)
Function 03h, to load an overlay (program) without executing it.
Although both functions perform their loading in the same way (relocation is
performed for EXE files) their handling of memory management is different.
FUNCTION 0: For function 0 to load and execute a program, EXEC first allocates
the largest availible block of memory (the new program's PSP will be at offset
0 in that block). Then EXEC loads the program. Thus, in most cases, the new
program owns all the memory from its PSP to the end of memory, including memory
occupied by the transient parent of COMMAND.COM. If the program were to issue
its own EXEC function call to load and execute another program, the request
would fail because no availible memory exists to load the new program into.
NOTE: For EXE programs, the amount of memory allocated is the size of the
program's memory image plus the value in the MAX_ALLOC field of the file's
header (offset 0Ch, if that much memory is availible. If not, EXEC
allocates the size of the program's memory image plus the value in the
MIN_ALLOC field in the header (offset 0Ah). These fields are set by the
Linker).
A well-behaved program uses the SETBLOCK function call when it receives
control, to shrink its allocated memory block down to the size it really needs.
A COM program should remember to set up its own stack before doing the SETBLOCK,
since it is likely that the default stack supplied by DOS lies in the area of
memory being used. This frees unneeded memory, which can be used for loading
other programs.
If the program requires additional memory during processing, it can obtain
the memory using the allocate function call and later free it using the free
memory function call.
When a program is loaded using EXEC function call 00h exits, its initial
allocation block (the block beginning with its PSP) is automatically freed
before the calling program regains control. It is the responsibility of all
programs to free any memory they allocate before exiting to the calling
program.
FUNCTION 3: For function 3, to load an overlay, no PSP is built and EXEC
assumes the calling program has already allocated memory to load the new program
into - it will NOT allocate memory for it. Thus the calling program should
either allow for the loading of overlays when it determines the amount of memory
to keep when issuing the SETBLOCK call, or should initially free as much memory
as possible. The calling program should then allocate a block (based on the size
of the program to be loaded) to hold the program that will be loaded using the
"load overlay" call. Note that "load overlay" does not check to see if the
calling program actually owns the memory block it has been instructed to load
into - it assumes the calling program has followed the rules. If the calling
program does not own the memory into which the overlay is being loaded, there is
a chance the program being loaded will overlay one of the control blocks that
DOS uses to keep track of memory blocks.
Programs loaded using function 3 should not issue any SETBLOCK calls since
they don't own the memory they are operating in. (This memory is owned by the
calling program)
Because programs loaded using function 3 are given control directly by (and
return contrrol directly to) the calling program, no memory is automatically
freed when the called program exits. It is up to the calling program to
determine the disposition of the memory that had been occupied by the exiting
program. Note that if the exiting program had itself allocated any memory, it
is responsible for freeing that memory before exiting.
Memory control blocks, sometimes called "arena headers" after their UNIX
counterpart, are 16 bytes long. Only the first 5 bytes are used. 16 bytes are
used for the memory control block, which always starts at a paragraph boundary.
When DOS call 48h is made to allocate "x" many paragraphs of memory, the amount
used up is actually one more than the figure in the BX register to provide
space for the associated memory control block. The location of the memory
control block is at the paragraph immediately before the segment value returned
in AX by the DOS function 48h call i.e. ((AX-1):0).
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� M E M O R Y C O N T R O L B L O C K �
쳐컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� Bytes � Function �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0 � ASCII M or Z �
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� 1-2 � PSP segment address of the program that owns this block of memory �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 3-4 � Size of next MCB in 16-byte paragraphs �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 5-F � unused �
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byte 1 will always have the value of 4Dh or 5Ah. The value 5Ah (Z) indicates
the block is the last in a chain, all memory above it is unused. 4Dh
(M) means that the block is intermediate in a chain, the memory above
it belongs to the next program or to DOS.
byte 2,3 hold the PSP segment address of the program that owns the
corresponding block of memory. A value of 0 means the block is free
to be claimed, any other value represents a segment address.
byte 3, 4 indicate the size in paragraphs of the memory block. If you know the
address of the first block, you can find the next block by adding the
length of the memory block plus 1 to the segment address of the
control block. Finding the first block can be difficult, as this
varies according to the DOS version and the configuration.
The remaining 11 bytes are not currently used by DOS, and may contain "trash"
characters left in memory from previous applications.
If DOS determines that the allocation chain of memory control blocks has been
corrupted, it will halt the system and display the message "Memory Allocation
Error", and the system will halt, requiring a reboot.
Each memory block consists of a signature byte (4Dh or 5Ah) then a word which
is the PSP value of the owner of the block (which allocated it), followed by a
word which is the size in paragraphs of the block. The last block has a
signature of 5Ah. All others have 4Dh. If the owner is 0000 then the block is
free.
Once a memory control block has been created it should only be manipulated
with the appropriate DOS function calls. Accidentally writing over any of the
first 5 bytes of a memory control block can cause a memory allocation error
and cause the system to lock up. If the first byte is overwritten with
something other than an 'M' or a 'Z' then DOS will complain with an error
return code of 7 signifying "Memory Control Blocks destroyed". However, should
you change the ownership or block size bytes, you've had it.
When a .COM program is first loaded by DOS and given control, the memory
control block immediately preceding the Program Segment Prefix contains the
following data:
ID = 'Z'
Owner = segment address of PSP (= CS register of .COM program)
Size = number of available paragraphs in DOS memory pool
An .EXE file will have the following data in the memory control block for
the program (just prior to the PSP):
ID = 'M'
Owner = segment address of PSP (= DS register of program)
Size = the number of paragraphs allocated to the program according
to the information in the .EXE program header
In the case of an .EXE program file the amount of memory allocated depends
on the contents of the program header which informs the DOS loader how much to
allocate for each of the segments in the program. With an .EXE program file
there will always be a 'Z' memory control block created in memory immediately
after the end of the space allocated to the program itself.
One important fact to remember about DOS memory allocation is that blocks of
RAM allocated by different calls to DOS function 48H will NOT be contiguous. At
the very best, they will be separated by the 16 bytes of the memory control
block, and at worst they could be anywhere in RAM that DOS manages to find a
existing memory control block of sufficient size to accomodate the memory
request.
DOS treats the memory control blocks as a kind of linked list (term used
loosely). It uses the earlier MCBs to find the later ones by calculating the
location of the next one from the size of the prior one. As such, erasing any
of the MCB data in the chain of MCBs will upset DOS severely, as each call for
a new memory allocation causes DOS to scan the whole chain of MCBs looking for
a free one that is large enough to fulfill the request.
A separate MCB is created for the DOS environment strings at each program
load, so there will be many copies of the environment strewn through memory
when you have a lot of memory resident programs loaded. The memory control
blocks for the DOS environment strings are not returned to the DOS memory pool
if the program goes resident, as DOS will need to copy this enviroment for the
next program loaded.
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
C H A P T E R S E V E N
DOS FILE STRUCTURE
FILE MANAGEMENT FUNCTIONS쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
Use DOS function calls to create, open, close, read, write, rename, find, and
erase files. There are two sets of function calls that DOS provides for support
of file management. They are:
* File Control Block function calls (0Fh-24h)
* Handle function calls (39h-69h)
Handle function calls are easier to use and are more powerful than FCB calls.
Microsoft recommends that the handle function calls be used when writing new
programs. DOS 3.0 up have been curtailing use of FCB function calls; it is
possible that future versions of DOS may not support FCB function calls.
The following table compares the use of FCB calls to Handle function calls:
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� FCB Calls � Handle Calls �
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� Access files in current � Access files in ANY directory �
� directory only. � �
� � �
� Requires the application � Does not require use of an FCB. �
� program to maintain a file � Requires a string with the drive, �
� control block to open, � path, and filename to open, create, �
� create, rename or delete � rename, or delete a file. For file �
� a file. For I/O requests, � I/O requests, the application program �
� the application program � must maintain a 16 bit file handle �
� also needs an FCB � that is supplied by DOS. �
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The only reason an application should use FCB function calls is to maintain
the ability to run under DOS 1.x. To to this, the program may use only function
calls 00h-2Eh. Though the FCB function calls are frowned upon, many of the
introductory assembly language programming texts use the FCB calls as examples.
FCB FUNCTION CALLS 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
FCB function calls require the use of one File Control Block per open file,
which is maintained by the application program and DOS. The application program
supplies a pointer to the FCB and fills in ther appropriate fields required by
the specific function call. An FCB function call can perform file management on
any valid drive, but only in the current logged directory. By using the current
block, current record, and record length fields of the FCB, you can perform
sequential I/O by using the sequential read or write function calls. Random I/O
can be performed by filling in the random record and record length fields.
Several possible uses of FCB type calls are considered programming errors and
should not be done under any circumstances to avoid problems with file sharing
and compatibility with later versions of DOS.
Some errors are:
1) If program uses the same FCB structure to access more than one open file. By
opening a file using an FCB, doing I/O, and then replacing the filename field
in the file control block with a new filename, a program can open a second
file using the same FCB. This is invalid because DOS writes control info-
rmation about the file into the reserved fields of the FCB. If the program
then replaces the filename field with the original filename and then tries to
perform I/O on this file, DOS may become confused because the control info-
rmation has been changed. An FCB should never be used to open a second file
without closing the one that is currently open. If more than one File Control
Block is to be open concurrently, separate FCBs should be used.
2) A program should never try to use the reserved fields in the FCB, as the
function of the fields changes with different versions of DOS.
3) A delete or a rename on a file that is currently open is considered an error
and should not be attempted by an application program.
It is also good programming practice to close all files when I/O is done. This
avoids potential file sharing problems that require a limit on the number of
files concurrently open using FCB function calls.
HANDLE FUNCTION CALLS쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
The recommended method of file management is by using the extended "handle"
set of function calls. These calls are not restricted to the current directory.
Also, the handle calls allow the application program to define the type of
access that other processes can have concurrently with the same file if the file
is being shared.
To create or open a file, the application supplies a pointer to an ASCIIZ
string giving the name and location of the file. The ASCIIZ string contains an
optional drive letter, optional path, mandatory file specification, and a
terminal byte of 00h. The following is an example of an ASCIIZ string:
format [drive][path] filename.ext,0
DB "A:\path\filename.ext",0
If the file is being created, the application program also supplies the
attribute of the file. This is a set of values that defines the file read
only, hidden, system, directory, or volume label.
If the file is being opened, the program can define the sharing and access
modes that the file is opened in. The access mode informs DOS what operations
your program will perform on this file (read-only, write-only, or read/write)
The sharing mode controls the type of operations other processes may perform
concurrently on the file. A program can also control if a child process inherits
the open files of the parent. The sharing mode has meaning only if file sharing
is loaded when the file is opened.
To rename or delete a file, the appplication program simply needs to provide
a pointer to the ASCIIZ string containing the name and location of the file
and another string with the new name if the file is being renamed.
The open or create function calls return a 16-bit value referred to as the
file handle. To do any I/O to a file, the program uses the handle to reference
the file. Once a file is opened, a program no longer needs to maintain the
ASCIIZ string pointing to the file, nor is there any need to stay in the same
directory. DOS keeps track of the location of the file regardless of what
directory is current.
Sequential I/O can be performed using the handle read (3Fh) or write (40h)
function calls. The offset in the file that IO is performed to is automatically
moved to the end of what was just read or written. If random I/O is desired, the
LSEEK (42h) function call can be used to set the offset into the file where I/O
is to be performed.
SPECIAL FILE HANDLES쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
DOS reserves five special file handles for use by itself and applications
programs. They are:
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� 0000h � STDIN � standard input device (input can be redirected) �
� 0001h � STDOUT � standard output device (output can be redirected) �
� 0002h � STDERR � standard error output device (output cannot be redirected) �
� 0004h � STDAUX � standard auxiliary device �
� 0005h � STDPRN � standard printer device �
읕컴컴컴좔컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
These handles are predefined by DOS and can be used by an application program.
They do not need to be opened by a program, although a program can close these
handles. STDIN should be treated as a read-only file, and STDOUT and STDERR
should be treated as write-only files. STDIN and STDOUT can be redirected. All
handles inherited by a process can be redirected, but not at the command line.
These handles are very useful for doing I/O to and from the console device.
For example, you could read input from the keyboard using the read (3Fh)
function call and file handle 0000h (STDIN), and write output to the console
screen with the write function call (40h) and file handle 0001h (STDOUT). If
you wanted an output that could not be redirected, you could output it using
file handle 0002h (STDERR). This is very useful for error messages that must
be seen by a user.
File handles 0003h (STDAUX) and 0004h (STDPRN) can be both read from and
written to. STDAUX is typically a serial device and STDPRN is usually a parallel
device.
ASCII and BINARY MODE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
I/O to files is done in binary mode. This means that the data is read or
written without modification. However, DOS can also read or write to devices in
ASCII mode. In ASCII mode, DOS does some string processing and modification to
the characters read and written. The predefined handles are in ASCII mode when
initialized by DOS. All other file handles that don't refer to devices are in
binary mode. A program, can use the IOCTL (44h) function call to set the mode
that I/O is to a device. The predefined file handles are all devices, so the
mode can be changed from ASCII to binary via IOCTL. Regular file handles that
are not devices are always in binary mode and cannot be changed to ASCII mode.
The ASCII/BINARY bit was called "raw" in DOS 2.x, but it is called ASCII/BINARY
in DOS 3.x.
The predefined file handles STDIN (0000h) and STDOUT (0001h) and STDERR
(0002h) are all duplicate handles. If the IOCTL function call is used to change
the mode of any of these three handles, the mode of all three handles is
changed. For example, if IOCTL was used to change STDOUT to binary mode, then
STDIN and STDERR would also be changed to binary mode.
FILE I/O IN BINARY (RAW) MODE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
The following is true when a file is read in binary mode:
1) The characters ^S (scroll lock), ^P (print screen), ^C (control break) are
not checked for during the read. Therefore, no printer echo occurs if ^S or
^P are read.
2) There is no echo to STDOUT (0001h).
3) Read the number of specified bytes and returns immediately when the last
byte is received or the end of file reached.
4) Allows no editing of the ine input using the function keys if the input is
from STDIN (0000h).
The following is true when a file is written to in binary mode:
1) The characters ^S (scroll lock), ^P (print screen), ^C (control break) are
not checked for during the write. Therefore, no printer echo occurs.
2) There is no echo to STDOUT (0001h).
3) The exact number of bytes specified are written.
4) Does not caret (^) control characters. For example, ctrl-D is sent out as
byte 04h instead of the two bytes ^ and D.
5) Does not expand tabs into spaces.
FILE I/O IN ASCII (COOKED) MODE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
The following is true when a file is read in ASCII mode:
1) Checks for the characters ^C,^S, and ^P.
2) Returns as many characters as there are in the device input buffer, or the
number of characters requested, whichever is less. If the number of
characters requested was less than the number of characters in the device
buffer, then the next read will address the remaining characters in the
buffer.
3) If there are no more bytes remaining in the device input buffer, read a
line (terminated by ^M) into the buffer. This line may be edited with the
function keys. The characters returned terminated with a sequence of 0Dh,
0Ah (^M,^J) if the number of characters requested is sufficient to include
them. For example, if 5 characters were requested, and only 3 were entered
before the carriage return (0Dh or ^M) was presented to DOS from the console
device, then the 3 characters entered and 0Dh and 0Ah would be returned.
However, if 5 characters were requested and 7 were entered before the
carriage return, only the first 5 characters would be returned. No 0Dh,0Ah
sequence would be returned in this case. If less than the number of
characters requested are entered when the carriage return is received, the
characters received and 0Dh,0Ah would be returned. The reason the 0Ah
(linefeed or ^J) is added to the returned characters is to make the devices
look like text files.
4) If a 1Ah (^Z) is found, the input is terminated at that point. No 0Dh,0Ah
(CR,LF) sequence is added to the string.
5) Echoing is performed.
6) Tabs are expanded.
The following is true when a file is written to in ASCII mode:
1) The characters ^S,^P,and ^C are checked for during the write operation.
2) Expands tabs to 8-character boundaries and fills with spaces (20h).
3) Carets control characters, for example, ^D is written as two bytes, ^ and D.
4) Bytes are output until the number specified is output or a ^Z is
encountered. The number actually output is returned to the user.
NUMBER OF OPEN FILES ALLOWED쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The number of files that can be open concurrently is restricted by DOS. This
number is determined by how the file is opened or created (FCB or handle
function call) and the number specified by the FCBS and FILES commands in the
CONFIG.SYS file. The number of files allowed open by FCB function calls and the
number of files that can be opened by handle type calls are independent of one
another.
RESTRICTIONS ON FCB USAGE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
If file sharing is not loaded using the SHARE command, there are no
restrictions on the nuumber of files concurrently open using FCB function calls.
However, when file sharing is loaded, the maximum number of FCBs open is set
by the the FCBS command in the CONFIG.SYS file.
The FCBS command has two values you can specify, 'm' and 'n'. The value for
'm' specifies the number of files that can be opened by FCBs, and the value 'n'
specifies the number of FCBs that are protected from being closed.
When the maximum number of FCB opens is exceeded, DOS automatically closes the
least recently used file. Any attempt to access this file results in an int 24h
critical error message "FCB not availible". If this occurs while an application
program is running, the value specified for 'm' in the FCBS command should be
increased.
When DOS determines the least recently used file to close, it does not include
the first 'n' files opened, therefore the first 'n' files are protected from
being closed.
RESTRICTIONS ON HANDLE USAGE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The number of files that can be open simultaneously by all processes is
determined by the FILES command in the CONFIG.SYS file. The number of files a
single process can open depends on the value specified for the FILES command. If
FILES is greater than or equal to 20, a single process can open 20 files. If
FILES is less than 20, the process can open less than 20 files. This value
includes three predefined handles: STDIN, STDOUT, and STDERR. This means only
17 additional handles can be added. DOS 3.3 includes a function to use more than
20 files per application.
ALLOCATING SPACE TO A FILE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
Files are not nescessarily written sequentially on a disk. Space is allocated
as needed and the next location availible on the disk is allocated as space for
the next file being written. Therefore, if considerable file generation has
taken place, newly created files will not be written in sequential sectors.
However, due to the mapping (chaining) of file space via the File Allocation
Table (FAT) and the function calls availible, any file may be used in either a
sequential or random manner.
Space is allocated in increments called clusters. Cluster size varies
according to the media type. An application program should not concern itself
with the way that DOS allocates space to a file. The size of a cluster is only
important in that it determines the smallest amount of space that can be
allocated to a file. A disk is considered full when all clusters have been
allocated to files.
MSDOS / PCDOS DIFFERENCES쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
There is a problem of compatibility between MS-DOS and IBM PC-DOS having to
do with FCB Open and Create. The IBM 1.0, 1.1, and 2.0 documentation of OPEN
(call 0Fh) contains the following statement:
"The current block field (FCB bytes C-D) is set to zero [when an FCB is
opened]."
This statement is NOT true of MS-DOS 1.25 or MS-DOS 2.00. The difference is
intentional, and the reason is CP/M 1.4 compatibility. Zeroing that field is
not CP/M compatible. Some CP/M programs will not run when machine translated if
that field is zeroed. The reason it is zeroed in the IBM versions is that IBM
specifically requested that it be zeroed. This is the reason for the complaints
from some vendors about the fact that IBM MultiPlan will not run under MS-DOS.
It is probably the reason that some other IBM programs don't run under MS-DOS.
NOTE: Do what all MS/PC-DOS systems programs do: Set every single FCB field you
want to use regardless of what the documentation says is initialized.
.COM FILE STRUCTURE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
The COM file structure was designed for DOS 1.0 and maximum compatibility
with programs ported from the CP/M operating system. COM files normally
comprise one segment only.
.EXE FILE STRUCTURE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
The EXE file is the native mode for DOS. EXE files may make use of multiple
segments for code, stack, and data. The design of the EXE file reflects the
segmented design of the Intel 80x86 CPU architecture. EXE files may be as
large as availible memory and may make references to specific segment addresses.
The EXE files produced by the Linker program consist of two parts, control and
relocation information and the load module itself.
The control and relocation information, which is described below, is at the
beginning of the file in an area known as the header. The load module
immediately follows the header. The load module begins in the memory image of
the module contructed by the Linker.
When you are loading a file with the name *.EXE, DOS does NOT assume that it
is an EXE format file. It looks at the first two bytes for a signature telling
it that it is an EXE file. If it has the proper signature, then the load
proceeds. Otherwise, it presumes the file to be a .COM format file.
If the file has the EXE signature, then the internal consistency is checked.
Pre-2.0 versions of MSDOS did not check the signature byte for EXE files.
The .EXE format can support programs larger than 64K. It does this by
allowing separate segments to be defined for code, data, and the stack, each
of which can be up to 64K long. Programs in EXE format may contain explicit
references to segment addresses. A header in the EXE file has information for
DOS to resolve these references.
The .EXE header is formatted as follows:
旼컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Offset � C O N T E N T S �
쳐컴컴컴컴탠컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 00h � 4Dh � This is the Linker's signature to mark the file as a valid �
쳐컴컴컴컴탠컴컴� .EXE file (The ASCII letters M and Z, for Mark Zbikowski, �
� 01h � 5Ah � one of the major designers of DOS at Microsoft) �
쳐컴컴컴컴탠컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 02h-03h � Length of the image mod 512 (remainder after dividing the load �
� � module image size by 512) �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 04h-05h � Size of the file in 512 byte pages including the header. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 06h-07h � Number of relocation table items following the header. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 08h-09h � Size of the header in 16 byte increments (paragraphs). This is �
� � used to locate the beginning of the load module in the file. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0Ah-0Bh � Minimum number of 16 byte paragraphs required above the end of �
� � the loaded program. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0Ch-0Dh � Maximum number of 16 byte paragraphs required above the end of �
� � the loaded program. If the minimum and maximum number of �
� � paragraphs are both zero, the program will be loaded as high in �
� � memory as possible. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0Eh-0Fh � Displacement in paragraphs of stack segment within load module. �
� � This size must be adjusted by relocation. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 10h-11h � Offset to be in SP register when the module is given control. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 12h-13h � Word Checksum - negative sum of all the words in the file, �
� � ignoring overflow. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 14h-15h � Offset to be in the IP register when the module is given control. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 16h-17h � Displacement in paragraphs of code segment within load module. �
� � This size must be adjusted by relocation. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 18h-19h � Displacement in bytes of the first relocation item in the file. �
쳐컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 1Ah-1Bh � Overlay number (0 for the resident part of the program) �
읕컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
THE RELOCATION TABLE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The word at 18h locates the first entry in the relocation table. The
relocation table is made up of a variable number of relocation items. The number
of items is contained at offset 06-07. The relocation item contains two fields
- a 2 byte offset value, followed by a 2 byte segment value. These two fields
represent the displacement into the load module before the module is given
control. The process is called relocation and is accomplished as follows:
1. The formatted part of the header is read into memory. Its size is 1Bh.
2. A portion of memory is allocated depending on the size of the load module
and the allocation numbers in offsets 0Ah-0Ch and 0Ch-0Dh. DOS always
tries to allocate 0FFFFh paragraphs. Since this call will always fail,
the function returns the amount of free memory. If this block is larger
than the minimum specified at offset 0Ah and the loaded program size,
DOS will allocate the size specified at offset 0Ch or the largest free
memory space, whichever is less.
3. A Program Segment Prefix is built following the resident portion of the
program that is performing the load operation.
4. The formatted part of the header is read into memory (its size is at
offset 08h)
5. The load module size is determined by subtracting the header size from the
file size. Offsets 04h and 08h can be used for this calculation. The
actual size is downward adjusted based on the contents of offsets 02-03.
Note that all files created by the Linker programs prior to version 1.10
always placed a value of 4 at this location, regardless of the actual
program size. Therefore, Microsoft recommends that this field be ignored if
it contains a value of 4. Based on the setting of the high/low loader switch,
an appropriate segment is determined for loading the load module. This
segment is called the start segment.
6. The load module is read into memory beginning at the start segment. The
relocation table is an ordered list of relocation items. The first relocation
item is the one that has the lowest offset in the file.
7. The relocation table items are read into a work area one or more at a time.
8. Each relocation table item segment value is added to the start segment value.
The calculated segment, in conjunction with the relocation item offset value,
points to a word in the load module to which is added the start segment
value. The result is placed back into the word in the load module.
9. Once all the relocation items have been processed, the SS and SP registers
are set from the values in the header and the start segment value is added
to SS. The ES and DS registers are set to the segment address of the program
segment prefix. The start segment value is added to the header CS register
value. The result, along with the header IP value, is used to give the
module control.
"NEW" .EXE FORMAT (Microsoft Windows and OS/2)쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The "old" EXE format is documented here. The "new" EXE format puts more
information into the header section and is currently used in applications that
run under Microsoft Windows. The linker that creates these files comes with the
Microsoft Windows Software Development Kit and is called LINK4. If you try to
run a Windows-linked program under DOS, you will get the error message "This
program requires Microsoft Windows".
PIF Files
PIF stands for "Program Information File". The PIF format was developed by
IBM for use with TopView, its multitasking manager. Microsoft also uses PIF
files to pass information regarding the amount of memory and type of I/O a
program running under Microsoft Windows requires.
The actual internal format of the PIF files is documented in the IBM TopView
Programmers' ToolKit.
STANDRD FILE CONTROL BLOCK쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The standard file control block is defined as follows, with offsets in hex:
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커
� F I L E C O N T R O L B L O C K �
쳐컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� Bytes � Function �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0 � 1 byte Drive number. For example: �
� � Before open: 00h = default drive �
� � 01h = drive A: �
� � 02h = drive B: etc. �
� � After open: 00h = drive C: �
� � 01h = drive A: �
� � 02h = drive B: etc. �
� � An 0 is replaced by the actual drive number during open. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 1-8 � 8 bytes Filename, left justified with blanks. If a reserved device �
� � name is placed here (such as PRN) do not include the optional colon. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 9-B � 3 bytes Filename extension, left justified with trailing blanks. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� C-D � 2 bytes Current block # relative to start of file, starting with 0 �
� � (set to 0 by the open function call). A block consists of 128 �
� � records, each of the size specified in the logical record size field.�
� � The current block number is used with the current record field �
� � (below) for sequential reads and writes. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� E-F � 2 bytes Logical record size in bytes. Set to 80h by OPEN function �
� � If this is not correct, you must set the value because DOS uses it �
� � to determine the proper locations in the file for all disk reads and �
� � writes. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 10-13 � 4 bytes File size in bytes. In this field, the first word is the �
� � low-order part of the size. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 14-15 � 2 bytes Date file was created or last updated. mm/dd/yy are mapped �
� � as follows: �
� � 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 �
� � y y y y y y y m m m m d d d d d �
� � where: mm is 1-12 �
� � dd is 1-31 �
� � yy is 0-119 (1980-2099) �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 16-17 � 2 bytes time file was created or last updated. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� � These bytes contain the time when the file was created or last �
� � updated. The time is mapped in the bits as follows: �
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� �
� � B Y T E 16h � B Y T E 17h � �
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� �
� � F E D C B A 9 8 � 7 6 5 4 3 2 1 0 � �
� 쳐컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴좔컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴� �
� � H H H H H � M M M M M M � D D D D D � �
� 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴� �
� � binary # hrs 0-23 � binary # minutes 0-59 � bin. # 2-sec incr � �
� 쳐컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴� �
� � note: The time is stored with the least significant byte first. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 18-19 � 2 bytes Reserved for DOS. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 20 �1 byte Current relative record number (0-127) within the current �
� � block. This field and the Current Block field at offset 0Ch make up �
� � the record pointer. This field is not initialized by the OPEN �
� � function call. You must set this field before doing sequential read- �
� � write operations to the diskette. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 21-25 � 4 bytes Relative Record. Points to the currently selected record, �
� � counting from the beginning of the file starting with 0. This field �
� � is not initialized by the OPEN system call. You must set this field �
� � before doing a random read or write to the file. �
� � If the record size is less than 64 bytes, both words are used. �
� � Otherwise, only the first 3 bytes are used. Note that if you use the �
� � File Control Block at 5Ch in the program segment, the last byte of �
� � the FCB overlaps the first byte of the unformatted parameter area. �
읕컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
note 1) An unopened FCB consists of the FCB prefix (if used), drive number, and
filename.ext properly filled in. An open FCB is one in which the
remaining fields have been filled in by the CREAT or OPEN function
calls.
2) Bytes 0-5 and 32-36 must be set by the user program. Bytes 16-31 are set
by DOS and must not be changed by user programs.
3) All word fields are stored with the least significant byte first. For
example, a record length of 128 is stored as 80h at offset 14, and 00h
at offset 15.
EXTENDED FILE CONTROL BLOCK쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
The extended file control block is used to create or search for files in the
disk directory that have special attributes.
It adds a 7 byte prefix to the FCB, formatted as follows:
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커
� E X T E N D E D F I L E C O N T R O L B L O C K �
쳐컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� Bytes � Function �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0 � Flag byte containing 0FFh to indicate an extended FCB. �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 1-6 � Reserved �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 6-7 � Attribute byte. Refer to function call 11h (search first) for �
� � details on using the attribute bits during directory searches. This �
� � function is present to allow applications to define their own files �
� � as hidden (and thereby excluded from normal directory searches) and �
� � to allow selective directory searches. �
읕컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
Any reference in the DOS function calls to an FCB, whether opened or unopened,
may use either a normal or extended FCB. If you are using an extended FCB, the
appropriate register should be set to the first byte of the prefix, rather than
the drive-number field.
Common practice is to refer to the extended FCB as a negative offset from the
first byte of a standard File Control Block.
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
C H A P T E R E I G H T
DOS DISK INFORMATION
C O N T E N T S
The DOS Area .......................................................... 8**1
The Boot Record ....................................................... 8**2
DOS File Allocation Table (FAT) ....................................... 8**3
Media Descriptor Byte ......................................... 8**4
12 Bit FATs ................................................... 8**5
16 Bit FATs ................................................... 8**6
DOS Disk Directory .................................................... 8**8
The Data Area ......................................................... 8**9
Floppy Disk Types ..................................................... 8**10
Hard Disk Layout ...................................................... 8**11
System Initialization ................................................. 8**12
Boot Record/Partition Table ........................................... 8**13
Hard Disk Technical Information ....................................... 8**14
Determining Hard Disk File Allocation ................................. 8**15
BIOS Disk Functions ................................................... 8**16
00h Reset
01h Get Status
02h Read Sectors
03h Write Sectors
04h Verify
05h Format Track (floppy disk)
06h Hard Disk - format track
07h Hard Disk - format drive
08h Read Drive Parameters
09h Initialize Two Fixed Disk Base Tables
0Ah Read Long (Hard disk)
0Bh Write Long (Hard disk)
0Ch Seek To Cylinder
0Dh Alternate Hard Disk Reset
0Eh Read Sector Buffer
0Fh Write sector buffer
10h Test For Drive Ready
11h Recalibrate Drive
12h Controller RAM Diagnostic
13h Controller Drive Diagnostic
14h Controller Internal Diagnostic
15h Get Disk Type
16h Get Disk Change Status (diskette)
17h Set Disk Type for Format (diskette)
18h Set Media Type For Format (diskette)
19h Park Hard Disk Heads
1Ah ESDI Hard Disk - Low Level Format
1Bh ESDI Hard Disk - Get Manufacturing Header
1Ch ESDI Hard Disk - Get Configuration
THE DOS AREA쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� 8**1
All disks and diskettes formatted by DOS are created with a sector size of 512
bytes. The DOS area (entire area for a diskette, DOS partition for hard disks)
is formatted as follows:
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커
� D O S A R E A �
쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� partition table - variable size (hard disk only) �
� boot record - 1 sector �
� first copy of the FAT - variable size �
� second copy of the FAT - same size as first copy �
� root directory - variable size �
� data area - variable depending on disk size �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
The following sections describe each of the allocated areas:
THE BOOT RECORD쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴 8**2
The boot record resides on track 0, sector 1, side 0 of every diskette
formatted by the DOS FORMAT program. For hard disks the boot record resides on
the first sector of the DOS partition. It is put on all disks to provide an
error message if you try to start up with a nonsystem disk in drive A:. If the
disk is a system disk, the boot record contains a JMP instruction pointing to
the first byte of the operating system.
If the device is IBM compatible the first sector of the first FAT must be
located at the same sector for all disk types. This is because the FAT sector
is read before the disk type is actually determined.
The information relating to the BPB for a particular media is kept in the
disk's boot sector. The format of the boot sector is:
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� D O S B O O T R E C O R D �
쳐컴쩡컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�00h�3 bytes� JMP to executable code. For DOS 2.x, 3 byte near jump (0E9h). �
� � � For DOS 3.x, 2 byte near jump (0EBh) followed by a NOP (90h) �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�03h�8 bytes� optional OEM name and version (such as IBM 2.1) �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�0Bh�2 bytes� bytes per sector �
쳐컴탠컴컴컴탠컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�0Dh� byte � � sectors per allocation unit (must be a power of 2) �
쳐컴탠컴컴컴� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�0Eh�2 bytes� B � reserved sectors (starting at logical sector 0) �
� � � � 01 for 1.x-3.31, 02 for 4.0+ �
쳐컴탠컴컴컴� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�10h� byte � � number of FATs �
쳐컴탠컴컴컴� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�11h�2 bytes� � maximum number of root directory entries �
쳐컴탠컴컴컴� P 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�13h�2 bytes� � number of sectors in logical image (total number of �
� � � � sectors in media, including boot sector directories, etc.)�
� � � � If logical disk size is geater than 32Mb, this value is 0 �
� � � � and the actual size is reported at offset 26h (DOS 4.0+) �
쳐컴탠컴컴컴� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�15h� byte � B � media descriptor byte �
쳐컴탠컴컴컴� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�16h�2 bytes� � number of sectors occupied by a single FAT �
쳐컴탠컴컴컴탠컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�18h�2 bytes� sectors per track �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�1Ah�2 bytes� number of heads �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�1Ch�2 bytes� # of hidden sectors (sectors before this volume) (1st part) �
읕컴좔컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� EXTENDED BOOT RECORD (DOS 4.0+) �
旼컴쩡컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�1Eh�2 bytes� # of hidden sectors (sectors before this volume) (2nd part) �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�20h�4 bytes� # sectors in this disk (see offset 13h, if 0) �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�24h�2 bytes� physical drive number (max 2 for DOS 4, max 8 for DOS 5) �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�26h� byte � extended boot record signature (29h) �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�27h�4 bytes� volume serial number (assigned with a random function) �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�2Bh�11 byte� volume label �
쳐컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
�36h�7 bytes� file system ID (FAT12 ), (FAT16 ) etc. ("reserved") �
읕컴좔컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
The three words at the end return information about the media. The number of
heads is useful for supporting different multihead drives that have the same
storage capacity but a different number of surfaces. The number of hidden
sectors is useful for drive partitioning schemes.
DOS 3.2 uses a table called the BIOS Parameter Block (BPB) to determine if a
disk has a valid File Allocation Table. The BPB is located in the first sector
of a floppy disk. Although the BPB is supposed to be on every formatted floppy
disk, some earlier versions of DOS did not create a BPB and instead assumed that
the FAT begins at the second sector of the disk and that the first FAT byte
(Media Descriptor Byte) describes the disk format.
DOS 3.2 reads in the whole of the BPB and tries to use it - although strangely
enough, it seems as if DOS is prepared to cope with a BPB that is more or less
totally blank (it seems to ignore the descriptor byte and treat it as a DSDD
9-sector disk).
DOS 3.2 determines if a disk has a valid boot sector by examining the first
byte of logical sector 0. If that byte it a jump instruction 0E9h, DOS 3.2
assumes the rest of the sector is a valid boot sector with a BPB. If the first
byte is not 0E9h DOS 3.2 behaves like previous versions, assumes the boot sector
is invalid and uses the first byte of the FAT to determine the media type.
If the first byte on the disk happens to be 0E9h, but the disk does not have a
BPB, DOS 3.2 will return a disk error message.
The real problems occur if some of the BPB data is valid and some isn't.
Apparently some OEMs have assumed that DOS would continue to ignore the
formatting data on the disk, and have failed to write much there during FORMAT
except the media descriptor byte (or, worse, have allowed random junk to be
written there). While this error is understandable, and perhaps even
forgiveable, it remains their problem, not IBM's, since the BPB area has always
been documented as containing the format information that IBM DOS 3.2 now
requires to be there.
When the BPB problems first became evident with DOS 3.2 a number of reports
circulated claiming DOS looked for the letters "IBM" in the OEM ID field. This
was incorrect. IBM DOS 4.0 *did* check for the letters "IBM" and would refuse
to recognize hard drives formatted under MSDOS 4.0. IBM corrected this with
their 4.01 revision.
THE DOS FILE ALLOCATION TABLE (FAT)쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴 8**3
The File Allocation Table, or FAT, has three main purposes:
1) to mark bad sectors on the media
2) to determine which sectors are free for use
3) to determine the physical location(s) of a file on the media.
DOS uses one of two schemes for defining the File Allocation Table:
1) a 12-bit FAT, for DOS 1.x, 2.x, all floppies, and small hard disks
2) a 16-bit FAT, for DOS 3.x+ hard disks from 16.8 to 32Mb
This section explains how DOS uses the FAT to convert the clusters of a file
into logical sector numbers. It is recommended that system utilities use the
DOS handle calls rather than interpreting the FAT, particularly since
aftermarket disk partitioning or formatting software may have been used.
The FAT is used by DOS to allocate disk space for files, one cluster at a time.
In DOS 4.0, clusters are referred to as "allocation units." It means the same
things; the smallest logical portion of a drive.
The FAT consists of a 12 bit entry (1.5 bytes) for each cluster on the disk or
a 16 bit (2 bytes) entry when a hard disk has more than 20740 sectors as is the
case with fixed disks larger than 10Mb.
The first two FAT entries map a portion of the directory; these FAT entries
contain indicators of the size and format of the disk. The FAT can be in a 12
or 16 bit format. DOS determines whether a disk has a 12 or 16 bit FAT by
looking at the total number of allocation units on a disk. For all diskettes
and hard disks with DOS partitions less than 20,740 sectors, the FAT uses a 12
bit value to map a cluster. For larger partitions, DOS uses a 16 bit value.
The second, third, and fourth bit applicable for 16 bit FAT bytes always
contains 0FFFFh. The first byte is used as follows:
Media Descriptor Byte ................................................. 8**4
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커
� M E D I A D E S C R I P T O R B Y T E �
쳐컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
쿴ex value � meaning � normally used �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 00 � hard disk � 3.3+ extended DOS partition �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� ED � double sided 9 sector 80 track � Tandy 2000 720k (5�) �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� F0 � double sided 18 sector diskette � PS/2 1.44 meg DSHD �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� F8 � hard disk � bootable hard disk at C:800 �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� F8 � 720k floppy, 9 sector 80 track � Sanyo 55x, DS-DOS 2.11 (5�) �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� F9 � double sided 15 sector diskette � AT 1.2 meg DSHD �
� � double sided 9 sector diskette � Convertible 720k DSQD �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� FA � IBM Displaywriter System disk � 287k �
� � Kodak "4 meg" (Pelican) � 4.4 meg (5�) �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� FB � IBM Displaywriter System disk � 1 meg (5�) �
� � Kodak "6 meg" (Pelican) � 5.5 meg (5�) �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� FC � single sided 9 sector diskette � DOS 2.0, 180k SSDD (5�) �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� FD � double sided 9 sector diskette � DOS 2.0, 360k DSDD (5�) �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� FF � double sided 36 sector diskette � Practidisk 2.88mb DSED (3�) �
� � single sided 8 sector diskette � DOS 1.0, 160k SSDD (5�) �
� � double sided 8 sector diskette � DOS 1.1, 320k SSDD (5�) �
� � hard disk � Sanyo 55x with DS-DOS 2.11 �
쳐컴컴컴컴컨컴컴컴컴컴컫컴컴컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
쿯or 8 inch diskettes: �
쳐컴컴컴컴컫컴컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커
� FD � double sided 26 sector diskette � IBM 3740 format DSSD �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� FE � single sided 26 sector diskette � IBM 3740 format SSSD �
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � double sided 8 sector diskette � IBM 3740 format DSDD �
읕컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
The third FAT entry begins mapping the data area (cluster 002).
NOTE: These values are provided as a reference. Therefore, programs should not
make use of these values.
Each entry contains three hexadecimal characters for 12-bit FATs or four for
16-bit FATs.
The possible entries are:
12-bit | 16-bit
|
000h | 0000h if the cluster is unused and available
0FF7h | 0FFF7h bad cluster (if not part of the allocation chain)
|
0FF0h-0FF7h | 0FFF0h-0FFF7h to indicate reserved clusters
|
0FF8h-0FFFh | 0FFF8h-0FFFFh to indicate the last cluster of a file (EOF)
|
xxxH | xxxxH any other hexadecimal numbers are the cluster
| number of the next cluster in the file. The
| cluster number is the first cluster in the file
| that is kept in the file's directory entry.
The file allocation table always occupies the sector or sectors immediately
following the boot record. If the FAT is larger than 1 sector, the sectors
occupy consecutive sector numbers. Two copies of the FAT are written, one
following the other, for integrity. The FAT is read into one of the DOS buffers
whenever needed (open, allocate more space, etc).
12 Bit File Allocation Table .......................................... 8**5
Obtain the starting cluster of the file from the directory entry.
Now, to locate each subsequent sector of the file:
1. Multiply the cluster number just used by 1.5 (each FAT entry is 1.5
bytes long).
2. The whole part of the product is offset into the FAT, pointing to the entry
that maps the cluster just used. That entry contains the cluster number of
the next cluster in the file.
3. Use a MOV instruction to move the word at the calculated FAT into a register.
4. If the last cluster used was an even number, keep the low order 12 bits of
the register, otherwise, keep the high order 12 bits.
5. If the resultant 12 bits are (0FF8h-0FFFh) no more clusters are in the file.
Otherwise, the next 12 bits contain the cluster number of the next cluster in
the file.
To convert the cluster to a logical sector number (relative sector, such as
that used by int 25h and 26h and DEBUG):
1. Subtract 2 from the cluster number
2. Multiply the result by the number of sectors per cluster.
3. Add the logical sector number of the beginning of the data area.
12-bit FAT if DOS partition is smaller than 32,680 sectors (16.340 MB).
16 Bit File Allocation Table .......................................... 8**6
Obtain the starting cluster of the file from the directory entry. Now to
locate each subsequent cluster of the file:
1. Multiply the cluster number used by 2 (each FAT entry is 2 bytes long).
2. Use the MOV word instruction to move the word at the calculated FAT offset
into a register.
3. If the resultant 16 bits are (0FF8h-0FFFFh) no more clusters are in the
file. Otherwise, the 16 bits contain the cluster number of the next cluster
in the file.
DOS Disk Directory .................................................... 8**8
The FORMAT command initially builds the root directory for all disks. Its
location (logical sector number) and the maximum number of entries are
available through the device driver interfaces.
Since directories other than the root directory are actually files, there is
no limit to the number of entries that they may contain.
All directory entries are 32 bytes long, and are in the following format:
旼컴컴컴쩡컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿽ffset � size � DISK DIRECTORY ENTRY
쳐컴컴컴탠컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 00h � 8 bytes � Filename
� 쳐컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � The first byte of the filename indicates the file status.
� � The file status byte may contain the following values:
� 쳐컴컴컫컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � 00h � Directory entry has never been used. This is used to limit
� � � the length of directory searches, for performance reasons.
� � 05h � Indicates that the first character of the filename actually
� � � has an 0EDh character.
� � 0E5h � Filename has been used but the file has been erased.
� � 2Eh � This entry is for a directory. If the second byte is also
� � � 2Eh, the cluster field contains the cluster number of this
� � � directory's parent directory. (0000h if the parent directory
� � � is the root directory). Otherwise, bytes 00h-0Ah are all
� � � spaces and the cluster field contains the cluster number of
� � � the directory.
� 쳐컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � Any other character is the first character of a filename. Filenames
� � are left-aligned and if necessary padded with blanks.
쳐컴컴컴탠컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 08h � 3 bytes � Filename extension if any
� 쳐컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � Three characters, left-aligned and padded with blanks if necessary.
� � If there is no file extension, this field contains all blanks
쳐컴컴컴탠컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0Bh � 1 byte � File attributes
� 쳐컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � The attribute byte is mapped as follows:
� 쳐컴컴쩡컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � hex 쿫it� meaning
� 쳐컴컴탠컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � 00h � � (no bits set) normal; can be read or written without
� � � � restriction
� � 01h � 0 � file is marked read-only. An attempt to open the file for
� � � � output using int 21h/fn 3Dh will fail and an error code
� � � � will be returned. This value can be used with other values
� � � � below.
� � 02h � 1 � indicates a hidden file. The file is excluded from normal
� � � � directory searches.
� � 04h � 2 � indicates a system file. The file is excluded from normal
� � � � directory searches.
� � 08h � 3 � indicates that the entry contains the volume label in the
� � � � first 11 bytes. The entry has no other usable information
� � � � and may exist only in the root directory.
� � 10h � 4 � indicates that the file is a subdirectory
� � 20h � 5 � indicates an archive bit. This bit is set to on whenever
� � � � the file is written to and closed. Used by BACKUP and
� � � � RESTORE.
� � � 6 � reserved, set to 0
� � � 7 � reserved, set to 0
� 쳐컴컴좔컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � note 1) Bits 6 and 7 may be used in OS/2.
� � note 2) Attributes 08h and 10h cannot be changed using int21/43h.
� � note 3) The system files IBMBIO.COM and IBMDOS.COM (or customized
� � equivalent) are marked as read-only, hidden, and system
� � files. Files can be marked hidden when they are created.
� � note 4) Read-only, hidden, system and archive attributes may be
� � changed with int21h/fn43h.
쳐컴컴컴탠컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0Ch � 10 bytes� Reserved by DOS; value unknown
쳐컴컴컴탠컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 16h � 2 bytes � File timestamp
� 쳐컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � These bytes contain the time when the file was created or last
� � updated. The time is mapped in the bits as follows:
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � B Y T E 16h � B Y T E 17h �
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � F E D C B A 9 8 � 7 6 5 4 3 2 1 0 �
� 쳐컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴좔컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴�
� � H H H H H � M M M M M M � D D D D D �
� 쳐컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴�
� � binary # hrs 0-23 � binary # minutes 0-59 � bin. # 2-sec incr �
� 쳐컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴�
� � note: The time is stored with the least significant byte first.
쳐컴컴컴탠컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 18h � 2 bytes � File datestamp
� 쳐컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � This area contains the date when the file was created or last
� � updated. The mm/dd/yy are mapped in the bits as follows:
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � B Y T E 18h � B Y T E 19h �
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � F E D C B A 9 8 � 7 6 5 4 3 2 1 0 �
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴쩡컴좔컴컴컴컴컴쩡컴컴컴컴컴컴컴컴컴�
� � Y Y Y Y Y Y Y � M M M M � D D D D D �
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴�
� � 0-119 (1980-2099) � 1-12 � 1-31 �
� 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴�
� � note: The date is stored with the least significant byte first.
쳐컴컴컴탠컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 1Ah � 2 bytes � First file cluster number
� 쳐컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � * (reserved in DOS 2, documented in DOS 3+)
� � This area contains the starting cluster number of the first cluster
� � in the file. The first cluster for data space on all fixed disks and
� � floppy disks is always cluster 002. The cluster number is stored
� � with the least significant byte first.
쳐컴컴컴탠컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 1Ch � 4 bytes � File size
� 쳐컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � This area contains the file size in bytes. The first word contains
� � the low order part of the size. Both words are stored with the least
� � significant byte first.
읕컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The Data Area ......................................................... 8**9
Allocation of space for a file (in the data area) is done only when needed
(it is not preallocated). The space is allocated one cluser (unit allocation)
at a time. A cluster is always one or more consecutive sector numbers, and all
of the clusters in a file are "chained" together in the FAT.
The clusters are arranged on disk to minimize head movement for multisided
media. All of the space on a track (or cylinder) is allocated before moving
on to the next track. This is accomplished by using the sequential sector
numbers on the lowest-numbered head, then all the sector numbers on the next
head, and so on until all sectors of all heads of the track are used. Then the
next sector used will be sector 1 of head 0 on the next track.
An interesting innovation that was introduced in MS-DOS 3.0: disk space that
is freed by erasing a file is not re-used immediately, unlike earlier versions
of DOS. Instead, free space is obtained from the area not yet used during the
current session, until all of it is used up. Only then will space that is freed
during the current session be re-used.
This feature minimizes fragmentation of files, since never-before-used space
is always contiguous. However, once any space has been freed by deleting a file,
that advantage vanishes at the next system boot. The feature also greatly
simplifies un-erasing files, provided that the need to do an un-erase is found
during the same session and also provided that the file occupies contiguous
clusters.
However, when one is using programs which make extensive use of temporary
files, each of which may be created and erased many times during a session,
the feature becomes a nuisance; it forces the permanent files to move farther
and farther into the inner tracks of the disk, thus increasing rather than
decreasing the amount of fragmentation which occurs.
The feature is implemented in DOS by means of a single 16-bit "last cluster
used" (LCU) pointer for each physical disk drive; this pointer is a part of
the physical drive table maintained by DOS. At boot time, the LCU pointer is
zeroed. Each time another cluster is obtained from the free-space pool (the
FAT), its number is written into the LCU pointer. Each time a fresh cluster
is required, the FAT is searched to locate a free one; in older versions of
DOS this search always began at Cluster 0000, but in 3.x it begins at the
cluster pointed to by the LCU pointer.
For hard disks, the size of the file allocation table and directory are
determined when FORMAT initializes it and are based on the size of the DOS
partition.
Floppy Disk Types ..................................................... 8**10
The following tables give the specifications for floppy disk formats:
IBM PC-DOS disk formats:
# of FAT size DIR total
sides (sectors)(entries) sectors
� sectors � DIR � sectors�
� /track 퀂ectors�/cluster�
� � � � � � �
旼컴컴쩡컫컴컴컴컫컨컫컴컨컴컫컨컫컨컫컨컫컨컫컴좔쩡컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 160k�5СDOS 1.0� 1 � 8 (40)� 1 � 4 � 64� 1 � 320쿚riginal PC-0, 16k mbd
� 320k�5СDOS 1.1� 2 � 8 (40)� 1 � 7 �112� 2 � 360쿛C-1, 64k mbd
� 180k�5СDOS 2.0� 1 � 9 (40)� 2 � 4 � 64� 1 � 640쿛C-2, 256k mbd
� 360k�5СDOS 2.0� 2 � 9 (40)� 2 � 7 �112� 2 � 720쿛C/XT
� 1.2M�5СDOS 3.0� 2 �15 (80)� 7 �14 �224� 1 �2400쿛C/AT, PC/RT, XT/286
� 720k�3コDOS 3.2� 2 � 9 (80)� 3 � 7 �112� 2 �1440쿎onvertible, PS/2 25+
�1.44M�3コDOS 3.3� 2 �18 (80)� 9 �14 �224� 1 �2880쿛S/2 50+
읕컴컴좔컨컴컴컴컨컴컨컴컴컴컨컴컨컴컨컴컨컴컨컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴�
various MS-DOS disk formats:
旼컴컴쩡컫컴컴컴컫컨컫컴컨컴컫컨컫컨컫컨컫컨컫컴좔쩡컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 200k�5С * � 1 �10 (40)� � � � � �
� 400k�5С * ** � 2 �10 (40)� � � � � �
� 800k�5С * � 2 �10 (80)� � � � � �
� 720k�2 � � � � � � � � 쿩enith SuperSport 2-inch
� 720k�5СDOS2.11� 2 � 9 (80)� 3 � 7 �112� 2 �1440쿟andy 2000 (discontinued)
�2.88M�3コ � 2 �36 (80)� � � � �5760쿛ractidisk 2.88mb floppy
�2720k�5С *** � 2 �17(192)� 8 � �272� 4 �5440쿛elican (Kodak 3.3Mb)(disc.)
�5570k�5С *** � 2 �17(384)� 8 � �272� 4 �10880Pelican (Kodak 6.6Mb)(disc.)
읕컴컴좔컨컴컴컴컨컴컨컴컴컴컨컴컨컴컨컴컨컴컨컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴�
* Michtron DS-DOS 2.11 Plus and one version of MS-DOS 3.11 (vendor unknown)
** TallTree JFormat program
*** Pelican driver source calls for 2 sectors/cluster, Norton Utils reports 4.
旼컴컴쩡컫컴컴컴컫컨컫컴컨컴컫컨컫컨컫컨컫컨컫컴좔쩡컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 400k�5СDOS2.11� 1 �10 (80)� � � � � 800쿏EC Rainbow SS/HD (disc.)
� 720k�5СDOS2.11� 2 퀆ariable number of sectors 쿣ictor 9000 PC (discont'd)
읕컴컴좔컨컴컴컴컨컴캑per track, more sectors on 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿽uter tracks than inner �
퀃racks. Special DSDD drive. �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴켸
Some oddball DOS versions specify "zero" heads in their data area. HP's
single-sided disk format (16 256-byte sectors/track, model unknown) uses a
zero-based parameter for the number of heads. Without special device driver
software to "fix" this, these disks are basically unusable by normal DOS.
A couple of people have reported that the IBM "Gearbox" industrial PC uses
an 800k 3.5 inch floppy with 10 sectors and 80 tracks. I've been unable to
confirm this.
Files in the data area are not necessarily written sequentially. The data area
space is allocated one cluster at a time, skipping over clusters already
allocated. The first free cluster found is the next cluster allocated,
regardless of its physical location on the disk. This permits the most efficient
utilization of disk space because clusters freed by erasing files can be
allocated for new files. Refer back to the description of the DOS FAT in this
chapter for more information.
SSDD single sided, double density (160-180k) 5�
DSDD double sided, double density (320-360k) 5�
DSQD double sided, quad density (720k) 5�, 3�, 2
DSHD double sided, high density (1.2-1.44M) 5�, 3�
DSED double sided, extra high density (2.88M) 3�
Much of the trouble with AT 1.2 meg drives has been through the inadverdent
use of quad density disks in the high density drives. The high density disks
use a higher-coercivity media than the quads, and quads are not completely
reliable as 1.2Mb. Make sure you have the correct disk for your application.
ROTATION SPEEDS:
720k, 3�" (unknown) note: Zenith has discontinued 2" floppies
720k, 3�" 300 RPM
1.44Mb, 3�" 300 RPM
360k, 5�" 300 RPM
720k, 5�" 300 RPM
1.2mb, 5�" 360 RPM (even when reading 360k diskettes)
all 8" 360 RPM
The Victor 9000's 5�" floppies could vary their rotational speed as required.
This allowed them to put 720k on a standard 360k floppy, using a constant
density throughout.
The Central Point CopyIIPC Option Board emulates the Macintosh GCR recording
format by varying the data rate instead of the rotational speed.
HARD DISK LAYOUT ...................................................... 8**11
The DOS hard disk routines perform the following services:
1) Allow multiple operating systems to be installed on the hard disk at the
same time.
2) Allow a user-selected operating system to be started from the hard disk.
I) In order to share the hard disk among operating systems, the disk may be
logically divided into 1 to 4 partitions. The space within a given
partition is contiguous, and can be dedicated to a specific operating
system. Each operating system may "own" only one partition in DOS versions
2.0 through 3.2. DOS 3.3 introduced the "Extended DOS Partition" which
allows multiple DOS partitions on the same hard disk. FDISK (or a
similar program from other DOS vendors) utility allows the user to select
the number, type, and size of each partition. The partition information is
kept in a partition table that is embedded in the master hard disk boot
record on the first sector of the disk. The format of this table varies
from version to version of DOS.
II) An operating system must consider its partition to be the entire disk,
and must ensure that its functions and utilities do not access other
partitions on the disk.
III) Each partition may contain a boot record on its first sector, and any
other programs or data that you choose, including a different operating
system. For example, the DOS FORMAT command may be used to format and
place a copy of DOS in the DOS partition in the same manner that a
diskette is formatted. You can use FDISK to designate a partition as
"active" (bootable). The master hard disk boot record causes that
partition's boot record to receive control when the system is
initialized. Additional disk partitions could be FORTH, UNIX, Pick,
CP/M-86, OS/2 HPFS, Concurrent DOS, Xenix, or the UCSD p-System.
SYSTEM INITIALIZATION ................................................. 8**12
The boot sequence is as follows:
1. System initialization first attempts to load an operating system from
diskette drive A. If the drive is not ready or a read error occurs, it then
attempts to read a master hard disk boot record on the first sector of the
first hard disk in the system. If unsuccessful, or if no hard disk is
present, it invokes ROM BASIC in an IBM PC or displays a disk error
message on most compatibles.
2. If initialization is successful, the master hard disk boot record is given
control and it examines the partition table embedded within it. If one of
the entries indicates an active (bootable) partition, its boot record is
read from the partition's first sector and given control.
3. If none of the partitions is bootable, ROM BASIC is invoked on an IBM PC or
a disk error on most compatibles.
4. If any of the boot indicators are invalid, or if more than one indicator is
marked as bootable, the message "INVALID PARTITION TABLE "is displayed and
the system stops.
5. If the partition's boot record cannot be successfully read within five
retries due to read errors, the message "ERROR LOADING OPERATING SYSTEM"
appears and the system stops.
6. If the partition's boot record does not contain a valid "signature", the
message "MISSING OPERATING SYSTEM" appears, and the system stops.
NOTE: When changing the size or location of any partition, you must ensure that
all existing data on the disk has been backed up. The partitioning program
will destroy the data on the disk.
System programmers designing a utility to initialize/manage a hard disk must
provide the following functions at a minimum:
1. Write the master disk boot record/partition table to the disk's first
sector to initialize it.
2. Perform partitioning of the disk - that is, create or update the partition
table information (all fields for the partition) when the user wishes
to create a partition. This may be limited to creating a partition for only
one type of operating system, but must allow repartitoning the entire disk,
or adding a partition without interfering with existing partitions (user's
choice).
3. Provide a means for marking a user-specified partition as bootable and
resetting the bootable indicator bytes for all other partitions at the same
time.
4. Such utilities should not change or move any partition information that
belongs to another operating system.
BOOT RECORD/PARTITION TABLE ........................................... 8**13
A boot record must be written on the first sector of all hard disks, and
must contain the following:
1. Code to load and give control to the boot record for one of four possible
operating systems.
2. A partition table at the end of the boot record. Each table entry is 16
bytes long, and contains the starting and ending cylinder, sector, and head
for each of four possible partitions, as well as the number of sectors
preceding the partition and the number of sectors occupied by the partition.
The "boot indicator" byte is used by the boot record to determine if one of
the partitions contains a loadable operating system. FDISK initialization
utilities mark a user-selected partition as "bootable" by placing a value
of 80h in the corresponding partition's boot indicator (setting all other
partitions' indicators to 0 at the same time). The presence of the 80h tells
the standard boot routine to load the sector whose location is contained in
the following three bytes. That sector is the actual boot record for the
selected operating system, and it is responsible for the remainder of the
system's loading process (as it is from the diskette). All boot records are
loaded at absolute address 0:7C00.
The partition table with its offsets into the boot record is:
旼컴컴컴컴컫컴컴컴컴컴쩡컴컴컴컴컫컴컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Offset � Offset � Offset � �
쿯rom Start쿯rom Start쿯rom Start� Size � Description
� of Disk � of Entry � of Disk � �
쳐컴컴컴컴컵컴컴컴컴컴탠컴컴컴컴컵컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � 00h � 0BEh � 1 byte � boot indicator
� � 01h � 0BFh � 1 byte � beginning head
� 1BEh � 02h � 0C0h � 1 byte � beginning sector
� (part 1) � 03h � 0C1h � 1 byte � beginning cylinder
� 16 bytes � 04h � 0C2h � 1 byte � system indicator
� � 05h � 0C3h � 1 byte � ending head
� � 06h � 0C4h � 1 byte � ending sector
� � 07h � 0C5h � 1 byte � ending cylinder
� � 08h � 0C6h � 4 bytes� relative (starting) sector
� � 0Ch � 0DAh � 4 bytes� number of sectors
쳐컴컴컴컴컵컴컴컴컴컴탠컴컴컴컴컵컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � 00h � 0DEh � 1 byte � boot indicator
� � 01h � 0DFh � 1 byte � beginning head
� 1CEh � 02h � 0E0h � 1 byte � beginning sector
� (part 2) � 03h � 0E1h � 1 byte � beginning cylinder
� 16 bytes � 04h � 0E2h � 1 byte � system indicator
� � 05h � 0E3h � 1 byte � ending head
� � 06h � 0E4h � 1 byte � ending sector
� � 07h � 0E5h � 1 byte � ending cylinder
� � 08h � 0E6h � 4 bytes� relative (starting) sector
� � 0Ch � 0EAh � 4 bytes� number of sectors
쳐컴컴컴컴컵컴컴컴컴컴탠컴컴컴컴컵컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � 00h � 0FEh � 1 byte � boot indicator
� � 01h � 0FFh � 1 byte � beginning head
� 1DEh � 02h � 0100h � 1 byte � beginning sector
� (part 3) � 03h � 0101h � 1 byte � beginning cylinder
� 16 bytes � 04h � 0102h � 1 byte � system indicator
� � 05h � 0103h � 1 byte � ending head
� � 06h � 0104h � 1 byte � ending sector
� � 07h � 0105h � 1 byte � ending cylinder
� � 08h � 0106h � 4 bytes� relative (starting) sector
� � 0Ch � 010Ah � 4 bytes� number of sectors
쳐컴컴컴컴컵컴컴컴컴컴탠컴컴컴컴컵컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� � 00h � 010Eh � 1 byte � boot indicator
� � 01h � 011Fh � 1 byte � beginning head
� 1EEh � 02h � 0110h � 1 byte � beginning sector
� (part 4) � 03h � 0111h � 1 byte � beginning cylinder
� 16 bytes � 04h � 0112h � 1 byte � system indicator
� � 05h � 0113h � 1 byte � ending head
� � 06h � 0114h � 1 byte � ending sector
� � 07h � 0115h � 1 byte � ending cylinder
� � 08h � 0116h � 4 bytes� relative (starting) sector
� � 0Ch � 011Ah � 4 bytes� number of sectors
쳐컴컴컴컴컵컴컴컴컴컴좔컴컴컴컴컵컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 1FEh � � 2 bytes� 055AAh signature
읕컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컨컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
Boot indicator (boot ind): The boot indicator byte must contain 0 for a non-
bootable partition or 80h for a bootable partition. Only one partition can be
marked as bootable at a time.
System Indicator (sys ind): The sys ind field contains an indicator of the
operating system that "owns" the partition. IBM PC-DOS can only "own" one
partition, though some versions of MSDOS allow all four partitions to be used
by DOS.
The system indicators are:
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� System Indicator (sys ind) �
쳐컴컴컴쩡컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 00h � unknown or no partition defined �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 01h � DOS 12 bit FAT (DOS 2.x all and 3.x+ under 16 Mb) �
� � less than 4086 clusters �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 02h � Xenix �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 03h � Xenix �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 04h � DOS 16 bit FAT (DOS 3.0+. Not recognized by 2.x) �
� � less than 65,536 sectors �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 05h � extended DOS partition, some 3.2 and all 3.3+ �
� � (pointer to further partition table) �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 06h � Compaq DOS 3.31, DOS 4.0+ partitions over 32 megs �
� � Digital Research DRDOS 3.4, 3.41 over 32 megs �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 06h � PC-MOS/386 partitions over 32 megs (NOT compatible �
� � with the DR, Compaq, and MSDOS big partitions! �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 07h � OS/2 High Performance File System �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 051h � Ontrack Disk Manager "read/write" partitions �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0DBh � DRI Concurrent DOS (>32mb partitions?)�
� � DRI Concurrent CP/M? �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0E4h � Speedstor, small partitions (?) (under 1024cyl?) �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0F2h � 2nd DOS partition, some OEM customized DOS 3.2 �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0F4h � Speedstor, large partitions (?) �
쳐컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� 0FEh � Speedstor, partitions >1024 cylinders �
읕컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
There are ID bytes for proprietary formatting schemes. Some manufacturers
(such as Zenith, Wyse, and Tandon) diddle with these system bytes to implement
more than one DOS partition per disk.
note 1) Xenix doesn't like extended DOS partitions a'la DOS 3.3, limiting you
to a DOS partition of 32Mb. Xenix doesn't recognize DOS 4.0x at all,
so to use it you need to boot from a floppy. Early versions of OS/2
also have this problem.
2) I have found one source listing Minix partitions as "40" and some
Unix partitions as "63". I don't know if these are decimal or
hexadecimal figures.
Cylinder (CYL) and Sector (S): The 1 byte fields labelled CYL contain the low
order 8 bits of the cylinder number - the high order 2 bits are in the high
order 2 bits of the sector (S) field. This corresponds with the ROM BIOS
interrupt 13h (disk I/O) requirements, to allow for a 10 bit cylinder number.
The fields are ordered in such a manner that only two MOV instructions are
required to properly set up the DX and CX registers for a ROM BIOS call to
load the appropriate boot record (hard disk booting is only possible from the
first hard disk in the system, where a BIOS drive number of 80h corresponds
to the boot indicator byte).
All partitions are allocated in cylinder multiples and begin on sector 1,
head 0, with the exception that the partition that is allocated at the beginning
of the disk starts at sector 2, to account for the hard disk's master boot
record.
Relative (starting) Sector: The number of sectors preceding each partition
on the disk is kept in this 4 byte field. This value is determined by counting
the sectors beginning with cylinder 0, sector 1, head 0 of the disk, and
incrementing the sector, head, and then track values up to the beginning of
the partition. This, if the disk has 17 sectors per track and 4 heads, and the
second partition begins at cylinder 1, sector 1, head 0, then the partition's
starting relative sector is 68 (decimal) - there were 17 sectors on each of 4
heads on 1 track allocated ahead of it. The field is stored with the least
significant word first.
Number of sectors (#sects): The number of sectors allocated to the partition
is kept in the "# of sects" field. This is a 4 byte field stored least
significant word first.
Signature: The last 2 bytes of the boot record (55AAh) are used as a signature
to identify a valid boot record. Both this record and the partition boot record
are required to contain the signature at offset 1FEh.
HARD DISK TECHNICAL INFORMATION ....................................... 8**14
Western Digital's hard disk installation manuals make the claim that MSDOS
can support only 2 hard drives. This is entirely false, and their purpose for
making the claim is unclear. DOS merely performs a function call pointed at
the hard disk driver, which is normally in one of three locations; a ROM at
absolute address C:800, the main BIOS ROM if the machine is an AT, or a device
driver installed through the CONFIG.SYS file. Two hard disk controller cards
can normally not reside in the same machine due to lack of interrupt
arbitration. Perstor's ARLL controller and some cards marketed by Novell can
coexist with other controllers. Perstor's technical department has had four
controllers and eight hard disks in the same IBM XT functioning concurrently.
A valid hard disk has a boot record arranged in the following manner:
db drive ; 0 or 80h (80h marks a bootable, active
partition)
db head1 ; starting head
dw trksec1 ; starting track/sector (CX value for INT 13)
db system ; SYS IND ID from table above
db head2 ; ending head
dw trksec2 ; ending track/sector
dd sector1 ; absolute # of starting sector
dd sector2 ; absolute # of last sector
The master disk boot record invokes ROM BASIC if no indicator byte reflects a
bootable system.
When a partition's boot record is given control, it is passed its partition
table entry address in the DS:SI registers.
DETERMINING HARD DISK ALLOCATION ...................................... 8**15
DOS determines disk allocation using the following formula:
D * BPD
TS - RS - 컴컴컴컴컴�
BPS
SPF = 컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
BPS * SPC
CF + 컴컴컴컴컴컴컴
BPC
where:
TS Total number of sectors on the disk
RS The number of sectors at the beginning of the disk that are
reserved for the boot record. DOS normally reserves 1 sector.
D The number of directory entries in the root directory.
BPD The number of bytes per directory entry. This is always 32.
BPS The number of bytes per logical sector. Typically 512, but you can
specify a different number with VDISK.
CF The number of FATS per disk. Usually 2. VDISK is 1.
SPF The number of sectors per FAT. Maximum 64.
SPC The number of sectors per allocation unit (cluster).
BPC The number of bytes per FAT entry. BPC is 1.5 for 12 bit FATs.
2 for 16 bit FATS.
To calculate the minimum partition size that will force a 16-bit FAT:
CYL = (max clusters * 8)/(HEADS * SPT)
where:
CYL number of cylinders on the disk
max clusters 4092 (maximum number of clusters for a 12 bit FAT)
HEADS number of heads on the hard disk
SPT sectors per track (normally 17 on MFM)
DOS 2.0 through 3.3 limit partition sizes to 32 megabytes. The limit arises
from the fact that DOS does things by sector number, and each sector is stored
as a word. So the largest sector number DOS can count to is 64k. As each
sector is 512 bytes long, 64k * .5k = 32Mb. The easiest way for an aftermarket
disk handler to break the 32Mb barrier is probably to increase the sector size
- with 2k sectors, maximum partiton size increases to 128Mb. However, the BIOS
boot routines and IBMBIO.COM are hardwired for 512 byte sectors, so you won't
be able to boot from a drive with oversize sectors. That's why Disk Manager
formats a small boot partition by default.
DOS 2.x uses a "first fit" algorithm when allocating file space on the hard
disk. Each time an application requests disk space, it will scan from the
beginning of the FAT until it finds a contiguous peice of storage large enough
for the file.
DOS 3.x+ keeps a pointer into the disk space, and begins its search from the
point it last left off. This pointer is lost when the system is rebooted.
This is called the "next fit" algorithm. It is faster than the first fit and
helps minimize fragmentation.
In either case, if the FCB function calls are used instead of the handle
function calls, the file will be broken into pieces starting with the first
available space on the disk.
BIOS Disk Routines .................................................... 8**16
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
쿔nterrupt 13h Disk I/O - access the disk drives (floppy and hard disk) �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
(0:004Ch) 1) These calls do not try rereading disk if an error is returned.
2) In the IBM OS/2 Tech Ref Volume 1, page 7-33, under "DOS
Environment Software Interrupt Support", it lists:
13h disk/diskette for non-removable media only, these
functions are supported:
01h read status
02h read sectors
0Ah read long
15h read DASD (disk) type
3) On hard disk systems these calls may be vectored through the
int 40h hard disk BIOS.
Function 00h Reset - reset the disk controller chip
entry AH 00h
DL drive (if bit 7 is set both hard disks and floppy disks reset)
00h-7Fh floppy disk
80h-0FFh hard disk
return AH status (see 01h below)
note 1) Forces controller chip to recalibrate read/write heads.
2) Some systems (Sanyo 55x, Columbia MPC) this resets all drives.
3) This function should be called after a failed floppy disk Read, Write,
Verify, or Format request before retrying the operation.
4) If called with DL >= 80h (i.e., selecting a hard drive), the floppy
controller and then the hard disk controller are reset.
5) Function 0Dh allows the hard disk controller to be reset without
affecting the floppy controller.
Function 01h Get Status of Disk System
entry AH 01h
DL drive (hard disk if bit 7 set)
00h-7Fh floppy disk
80h-0FFh hard disk
return AH 00h
AL status of most recent disk operation
00h successful completion, no errors
01h bad command
02h address mark not found
03h tried to write on write-protected disk (floppy only)
04h sector not found
05h reset failed (hard disk)
06h diskette removed or changed (floppy only)
07h bad parameter table (hard disk)
08h DMA overrun (floppy only)
09h attempt to DMA across 64K boundary
0Ah bad sector detected (hard disk)
0Bh bad track detected (hard disk)
0Ch unsupported track or media type not found (floppy disk)
0Dh invalid number of sectors on format (hard disk)
0Eh control data address mark detected (hard disk)
0Fh DMA arbitration level out of range (hard disk)
10h uncorrectable CRC/EEC on read
11h ECC corrected data error (hard disk)
20h controller failure
40h seek failed
80h timeout
0AAh drive not ready (hard disk)
0BBh undefined error (hard disk)
0CCh write fault (hard disk)
0E0h status error (hard disk)
0FFh sense operation failed (hard disk)
note 1) For hard disks, error code 11h (ECC data error) indicates that a
recoverable error was detected during a preceding int 13h fn 02h
(Read Sector) call.
Function 02h Read Sectors - read one or more sectors from diskette
entry AH 02h
AL number of sectors to read
BX address of buffer (ES=segment)
CH track (cylinder) number (0-39 or 0-79 for floppies)
(for hard disk, bits 8,9 in high bits of CL)
CL sector number (1 to 18, not value checked)
DH head number (0 or 1)
DL drive (0=A, 1=B, etc.) (bit 7=0) (drive 0-7)
00h-7Fh floppy disk
80h-FF0h hard disk
ES:BX address to store/fetch data (buffer to fill)
[0000:0078] dword pointer to diskette parameters
return CF clear successful
AL number of sectors transferred
set error
AH status (00h, 02h, 03h, 04h, 08h, 09h, 10h,
0Ah, 20h, 40h, 80h)
note 1) Number of sectors begins with 1, not 0.
2) Trying to read zero sectors is considered a programming error; results
are not defined.
3) For hard disks, the upper 2 bits of the 10-bit cylinder number are
placed in the upper 2 bits of register CL.
4) For hard disks, error code 11h indicates that a read error occurred
that was corrected by the ECC algorithm; in this case, AL contains the
burst length. The data read is good within the limits of the ECC code.
If a multisector transfer was requested, the operation was terminated
after the sector containing the read error.
5) For floppy drives, an error may result from the drive motor being off
at the time of the request. The BIOS does not automatically wait for
the drive to come up to speed before attempting the read operation. The
calling program should reset the floppy disk system with function 00h
and retry the operation three times before assuming that the error
results from some other cause.
Function 03h Write Sectors - write from memory to disk
entry AH 03h
AL number of sectors to write (1-8)
CH track number (for hard disk, bits 8,9 in high bits of CL)
CL beginning sector number
(if hard disk, high two bits are high bits of track #)
DH head number (head 0=0)
DL drive number (0-7)
00h-7Fh floppy disk
80h-FF0h hard disk
ES:BX address of buffer for data
return CF clear success
AL number of sectors written
set error
AH status (see 01h above)
note 1) Number of sectors begins with 1, not 0.
2) Trying to write zero sectors is considered a programming error; results
are not defined.
3) For hard disks, the upper 2 bits of the 10-bit cylinder number are
placed in the upper 2 bits of register CL.
4) For floppy drives, an error may result from the drive motor being off
at the time of the request. The BIOS does not automatically wait for
the drive to come up to speed before attempting the read operation. The
calling program should reset the floppy disk system with function 00h
and retry the operation three times before assuming that the error
results from some other cause.
Function 04h Verify - verify that a write operation was successful
entry AH 04h
AL number of sectors to verify (1-8)
CH track number (for hard disk, bits 8,9 in high bits of CL)
CL beginning sector number
DH head number
DL drive number (0-7)
DL drive number (0-7)
00h-7Fh floppy disk
80h-FF0h hard disk
ES:BX address of buffer for data
return CF set on error
AH status (see 01h above)
AL number of sectors verified
note 1) With IBM PC, XT, and AT with ROM BIOS earlier than 11/15/85, ES:BX
should point to a valid buffer.
2) For hard disks, the upper 2 bits of the 10-bit cylinder number are
placed in the upper 2 bits of register CL.
3) This function can be used to test whether a readable media is in a
floppy drive. An error may result from the drive motor being off at the
time of the request since the BIOS does not automatically wait for the
drive to come up to speed before attempting the verify operation. The
requesting program should reset the floppy disk system with function
00h and retry the operation three times before assuming that a readable
disk is not present.
Function 05h Format Track - write sector ID bytes for 1 track (floppy disk)
entry AH 05h
AL number of sectors to create on this track
interleave (for XT hard disk only)
CH track (or cylinder) number (bits 8,9 in high bits of CL)
CL sector number
DH head number (0, 1)
DL drive number (0-3)
00h-7Fh floppy disk
80h-0FFh hard disk
ES:BX pointer to 4-byte address field (C-H-R-N) (except XT hard disk)
byte 1 = (C) cylinder or track
byte 2 = (H) head
byte 3 = (R) sector
byte 4 = (N) bytes/sector (0 = 128, 1 = 256, 2 = 512, 3 = 1024)
return CF set if error occurred
AH status code (see 01h above)
note 1) Not valid for ESDI hard disks on PS/2.
2) For floppy disks, the number of sectors per track is taken from the
BIOS floppy disk parameter table whose address is stored in the vector
for int 1Eh.
3) When this function is used for floppies on ATs or the PS/2, it should
be preceded by a call to int 13h/fn 17h to select the type of media to
format.
4) For hard disks, the upper 2 bits of the 10-bit cylinder number are
placed in the upper 2 bits of CL.
5) On the XT/286, AT, and PS/2 hard disks, ES:BX points to a 512-byte
buffer containing byte pairs for each physical disk sector as follows:
Byte Contents
0 00h good sector
80h bad sector
1 sector number
For example, to format a track with 17 sectors and an interleave of
two, ES:BX would point to the following 34-byte array at the beginning
of a 512-byte buffer:
db 00h, 01h, 00h, 0Ah, 00h, 02h, 00h, 0Bh, 00h, 03h, 00h, 0Ch
db 00h, 04h, 00h, 0Dh, 00h, 05h, 00h, 0Eh, 00h, 06h, 00h, 0Fh
db 00h, 07h, 00h, 10h, 00h, 08h, 00h, 11h, 00h, 09h
Function 06h Hard Disk - format track and set bad sector flags
(PC2, PC-XT, and Portable)
entry AH 06h
AL interleave value (XT only)
CH cylinder number (bits 8,9 in high bits of CL)
CL sector number
DH head
DL drive (80h-0FFh for hard disk)
ES:BX 512 byte format buffer
the first 2*(sectors/track) bytes contain f,n for each sector
f 00h good sector
80h bad sector
n sector number
return CF error
AH status code (see 01h above)
Function 07h Hard Disk - format the drive starting at the desired track
(PC2, PC-XT and Portable)
entry AH 07h
AL interleave value (XT only) (01h-10h)
CH cylinder number (bits 8,9 in high bits of CL) (00h-03FFh)
CL sector number
DH head number (0-7)
DL drive number (80h-0FFh, 80h=C, 81h=D,...)
ES:BX format buffer, size = 512 bytes
the first 2*(sectors/track) bytes contain f,n for each sector
f 00h good sector
80h bad sector
n sector number
return CF set on error
AH status code (see 01h above)
note Award AT BIOS routines are extended to handle more than 1024 cylinders.
AL number of sectors
CH cylinder numberm low 8 bits
CL sector number bits 0-5, bits 6-7 are high 2 cylinder bits
DH head number (bits 0-5) bits 6-7 are extended high cyls (>1024)
DL drive number (0-1 for diskette, 80h-81h for hard disk)
ES:BX transfer address
Function 08h Read Drive Parameters (except PC, Jr)
entry AH 08h
DL drive number
00h-7Fh floppy disk
80h-0FFh hard disk
return CF set on error
AH status code (see above)
BL drive type (AT/PS2 floppies only)
01h if 360 Kb, 40 track, 5�"
02h if 1.2 Mb, 80 track, 5�"
03h if 720 Kb, 80 track, 3�"
04h if 1.44 Mb, 80 track, 3�"
CH low 8 bits of maximum useable value for cylinder number
CL bits 6-7 high-order 2 bits of maximum cylinder number
0-5 maximum sector number
DH maximum usable value for head number
DL number of consecutive acknowledging drives (0-2)
ES:DI pointer to drive parameter table
note 1) On the PC and PC/XT, this function is supported on hard disks only.
2) The Columbia MPC supports functions 6-14 for its hard disk. It returns
drive information, same as int 13 function 8, except that the BL and
ES:DI values are omitted and AL <- burst length.
Function 09h Initialize Two Fixed Disk Base Tables (XT, AT, XT/286, PS/2)
(install nonstandard drive)
entry AH 09h
DL 80h-0FFh hard disk number
return CF set on error
AH status code (see 01h above)
For PC, XT hard disks, the disk parameter block format is:
00h-01h maximum number of cylinders
02h maximum number of heads
03h-04h starting reduced write current cylinder
05h-06h starting write precompensation cylinder
07h maximum ECC burst length
08h drive options
bits 7 1 disable disk access retries
6 1 disable ECC retries
3-5 set to 0
0-2 drive option
09h standard timeout value
0Ah timeout value for format drive
0Bh timeout value for check drive
0Ch-0Fh reserved
For AT and PS/2 hard disks:
00h-01h maximum number of cylinders
02h maximum number of heads
03h-04h reserved
05h-06h starting write precompensation cylinder
07h maximum ECC burst length
08h drive options byte
bits 6-7 nonzero (10, 01, or 11) if retries disabled
5 1 if manufacturer's defect map present at
maximum cylinder + 1
4 not used
3 1 if more than 8 heads
0-2 not used
09h-0Bh reserved
0Ch-0Dh landing zone cylinder
0Eh sectors per track
0Fh reserved
note 1) For the XT, int 41h must point to the Disk Parameter Block.
2) For the AT and PS/2, int 41h points to table for drive 0 and int 46h
points to table for drive 1.
3) Initializes the hard disk controller for subsequent I/O operations
using the values found in the BIOS disk parameter block(s).
4) This function is supported on hard disks only.
Function 0Ah Read Long (Hard disk) (XT, AT, XT/286, PS/2)
entry AH 0Ah
CH cylinder number (bits 8,9 in high bits of CL)
CL sector number (upper 2 bits of cyl # in upper 2 bits of CL)
DH head number
DL drive ID (80h-0FFh hard disk)
ES:BX pointer to buffer to fill
return CF set on error
AH status code (see 01h above)
AL number of sectors actually transferred
note 1) A "long" sector includes a 4 byte EEC (Extended Error Correction) code.
2) Used for diagnostics only on PS/2 systems.
3) This function is supported on fixed disks only.
4) Unlike the normal Read Sector (02h) function, ECC errors are not
automatically corrected. Multisector transfers are terminated after any
sector with a read error.
Function 0Bh Write Long (XT, AT, XT/286, PS/2)
entry AH 0Bh
AL number of sectors
CH cylinder (bits 8,9 in high bits of CL)
CL sector number
DH head number
DL drive ID (80h-0FFh hard disk)
ES:BX pointer to buffer containing data
return CF set on error
AH status code (see 01h above)
AL number of sectors actually transferred
note 1) A "long" sector includes a 4 byte EEC (Extended Error Correction) code.
2) Used for diagnostics only on PS/2 systems.
3) Valid for hard disks only.
Function 0Ch Seek To Cylinder (except PC, PCjr)
entry AH 0Ch
CH lower 8 bits of cylinder
CL upper 2 bits of cylinder in bits 6-7
DH head number
DL drive number (0 or 1) (80h-0FFh for hard disk)
return CF set on error
AH status code (see 01h above)
note 1) Positions heads over a particular cylinder, but does not move any data.
2) This function is supported on hard disks only.
3) The upper 2 bits of the 10-bit cylinder number are placed in the upper
2 bits of CL.
4) The Read Sector, Read Sector Long, Write Sector, and Write Sector Long
functions include an implied seek operation and need not be preceded by
an explicit call to this function.
Function 0Dh Alternate Hard Disk Reset (except PC, PCjr)
entry AH 0Dh
DL hard drive number (80h-0FFh hard disk)
return CF set on error
AH status code (see 01h above)
note 1) Not for PS/2 ESDI hard disks.
2) Resets the hard disk controller, recalibrates attached drives (moves
the read/write arm to cylinder 0), and prepares for subsequent disk I/O.
3) This function is for hard disks only. It differs from fn 00h by not
resetting the floppy disk controller.
Function 0Eh Read Sector Buffer (XT, Portable, PS/2)
entry AH 0Eh
ES:BX pointer to buffer
return CF set on error
AH status code (see 01h above)
AL number of sectors actually transferred
note 1) Transfers controller's sector buffer. No data is read from the drive.
2) Used for diagnostics only on PS/2 systems.
3) This fn is supported by the XT's hard disk adapter only. It is "not
defined" for hard disk adapters on the AT or PS/2.
Function 0Fh Write sector buffer (XT, Portable)
entry AH 0Fh
ES:BX pointer to buffer
return CF set if error
AH status code (see 01h above)
AL number of sectors actually transferred
note 1) Should be called before formatting to initialize the controller's
sector buffer.
2) Used for diagnostics only on PS/2 systems.
3) Transfers data from system RAM to the hard disk adapter's internal
sector buffer.
4) No data is written to the physical disk drive.
5) This fn is for the XT hard disk controller only. It is "not defined"
for AT or PS/2 controllers.
Function 10h Test For Drive Ready (XT, AT, XT/286, PS/2)
entry AH 10h
DL hard drive number 0 or 1 (80h-0FFh)
return CF set on error
AH status code (see 01h above)
note 1) Tests whether the specified hard disk drive is operational and returns
the drive's status.
2) This function is supported on hard disks only.
3) Perstor and Novell controllers allow more than one controller. Does
not work for multiple Perstor controllers. (reports first two drives
only).
4) Does not work with network drives.
Function 11h Recalibrate Drive (XT, AT, XT/286, PS/2)
entry AH 11h
DL hard drive number (80h-0FFh hard disk)
return CF set on error
AH status code (see 01h above)
note 1) Causes the HD controller to recalibrate itself for the specified drive,
positioning the read/arm to cylinder 0, and returns the drive's status.
2) This function is for hard disks only.
Function 12h Controller RAM Diagnostics (XT, Portable, PS/2)
entry AH 12h
return CF set on error
AH status code (see fn 01h above)
note 1) Used for diagnostics only on PS/2 systems.
2) Makes the hard disk controller carry out a built-in diagnostic test on
its internal sector buffer.
Function 13h Controller Drive Diagnostic (XT, Portable, PS/2)
entry AH 13h
return CF set on error
AH status code (see 01h above)
note 1) Used for diagnostics only on PS/2 systems.
2) Causes HD controller to run internal diagnostic tests of the attached
drive, indicating whether the test was passed by the returned status.
3) This function is supported on XT HDs only.
Function 14h Controller Internal Diagnostic (AT, XT/286)
entry AH 14h
return CF set on error
AH status code (see 01h above)
note 1) OEM is Western Digital 1003-WA2 hard/floppy combination controller
in AT and XT/286.
2) Used for diagnostics only in PS/2 systems.
3) Causes HD controller to do a built-in diagnostic self-test, indicating
whether the test was passed by the returned status.
4) This function is supported on hard disks only.
Function 15h Get Disk Type (except PC and XT)
entry AH 15h
DL drive ID
00h-7Fh floppy disk
80h-0FFh fixed disk
return CF set on error
AH error code (see 01h above)
AH disk type
00h no drive is present
01h diskette, no change detection present
02h diskette, change detection present
03h hard disk
CX:DX number of 512-byte sectors
note 1) Returns a code indicating the type of disk referenced by the specified
drive code.
2) This function is not supported on the PC or XT.
Function 16h Get Disk Change Status (diskette) (except PC, XT, & Jr)
entry AH 16h
DL drive to check
return CF set on error
AH disk change status
00h no disk change
01h disk changed
DL drive that had disk change (00h-07Fh floppy disk)
note Returns the status of the change line, indicating whether the disk in
the drive may have been replaced since the last disk access. If this
function returns with CF set, the disk has not necessarily been
changed; the change line can be activated by simply unlocking and
relocking the disk drive door without removing the floppy disk.
Function 17h Set Disk Type for Format (diskette) (except PC and XT)
entry AH 17h
AL 00h not used
01h 160, 180, 320, or 360Kb diskette in 360kb drive
02h 360Kb diskette in 1.2Mb drive
03h 1.2Mb diskette in 1.2Mb drive
04h 720Kb diskette in 720Kb drive
DL drive number (0-7)
return CF set on error
AH status of operation (see 01h above)
note 1) This function is probably enhanced for the PS/2 series to detect
1.44 in 1.44 and 720k in 1.44.
2) This function is not supported for floppy disks on the PC or XT.
3) If the change line is active for the specified drive, it is reset.
4) The BIOS sets the data rate for the specified drive and media type.
The rate is 250k/sec for double-density media and 500k/sec for high
density media. The proper hardware is required.
Function 18h Set Media Type For Format (diskette) (AT, XT2, XT/286, PS/2)
entry AH 18h
CH lower 8 bits of number of tracks
CL high 2 bits of number of tracks (6,7) sectors per track
(bits 0-5)
DL drive number (0-7)
return CF clear no errors
AH 00h if requested combination supported
01h if function not available
0Ch if not suppported or drive type unknown
80h if there is no media in the drive
ES:DI pointer to 11-byte disk parameter table for media type
CF set error code (see 01h above)
note 1) A floppy disk must be present in the drive.
2) This function should be called prior to formatting a disk with Int 13h
Fn 05h so the BIOS can set the correct data rate for the media.
3) If the change line is active for the specified drive, it is reset.
Function 19h Park Hard Disk Heads (PS/2)
entry AH 19h
DL drive number (80h-0FFh)
return CF set on error
AH error code (see fn 01h)
note This function is defined for PS/2 fixed disks only.
Function 1Ah ESDI Hard Disk - Low Level Format (PS/2)
entry AH 1Ah
AL Relative Block Address (RBA) defect table count
00h no errors on disk
01h+ number of disk errors
CL format modifiers byte
bits 0 ignore primary defect map
1 ignore secondary defect map
2 update secondary defect map
3 perform extended surface analysis
4 generate periodic interrupt after each cylinder format
5 reserved - must be 0
6 reserved - must be 0
7 reserved - must be 0
DL drive (80h-0FFh)
ES:BX pointer to RBA defect table
return CF set on error
AH error code (see fn 01h above)
note 1) Initializes disk sector and track address fields on a drive attached
to the IBM "ESDI Fixed Disk Drive Adapter/A."
2) If periodic interrupt selected, int 15h/fn 0Fh is called after each
cylinder is formatted
3) If bit 4 of CL is set, Int 15h, AH=0Fh, AL=phase code after each
cylinder is formatted or analyzed. The phase code is defined as:
0 reserved
1 surface analysis
2 formatting
4) If bit 2 of CL is set, the drive's secondary defect map is updated to
reflect errors found during surface analysis. If both bit 2 and bit 1
are set, the secondary defect map is replaced.
5) For an extended surface analysis, the disk should first be formatted by
calling this function with bit 3 cleared and then analyzed by calling
this function with bit 3 set.
Function 1Bh ESDI Hard Disk - Get Manufacturing Header (PS/2)
entry AH 1Bh
AL number of record
DL drive
ES:BX pointer to buffer for manufacturing header (defect list)
return CF set on error
AH status
note Manufacturing header format (Defect Map Record format) can be found
in the "IBM 70Mb, 115Mb Fixed Disk Drives Technical Reference."
Function 1Ch ESDI Hard Disk - Get Configuration (PS/2)
entry AH 1Ch
AL 0Ah Get Device Configuration
DL drive
ES:BX pointer to buffer for device configuration
(drive physical parameter)
0Bh Get Adapter Configuration
ES:BX pointer to buffer for adapter configuration
0Ch Get POS Information
ES:BX pointer to POS information
0Dh unknown
0Eh Translate RBA to ABA
CH low 8 bits of cylinder number
CL sector number, high two bits of cylinder number
in bits 6 and 7
DH head number
DL drive number
ES:BX pointer to ABA number
return CF set on error
AH status (see 01h)
note 1) Device configuration format can be found in IBM ESDI Fixed Disk Drive
Adapter/A Technical Reference.
2) ABA (absolute block address) format can be found in IBM ESDI Adapter
Technical Reference by using its Device Configuration Status Block.
Function 1Dh IBMCACHE.SYS (PS/2 50+)
entry AH 1Dh
other parameters unknown
note IBMCACHE.SYS comes on the setup disk for MCA-bus PS/2 machines.
Function 20h Western Digital HD SuperBIOS
entry AH 20h
other parameters unknown
note SuperBIOS may be purchased separately from Western Digital and added
to standard HD controllers. SuperBIOS contains additional setup
tables and parameters.
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
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C H A P T E R N I N E
INSTALLABLE DEVICE DRIVERS
C O N T E N T S
Device Driver Format .................................................... 9**
Types of Devices ........................................................ 9**
Character Devices ............................................... 9**
Block Devices ................................................... 9**
Device Header ........................................................... 9**
Pointer to Next Device Header Field ............................. 9**
Attribute Field ................................................. 9**
Bits 0 and 1 ............................................ 9**
Bit 2 ................................................... 9**
Bit 3 ................................................... 9**
Bit 13 .................................................. 9**
Bit 14 .................................................. 9**
Bit 15 .................................................. 9**
Pointer to Strategy and Interrupt Routines ...................... 9**
Name/Unit Field ................................................. 9**
Creating a Device Driver ................................................ 9**
Installing Device Drivers ............................................... 9**
Installing Character Devices .................................... 9**
Installing Block Devices ........................................ 9**
Request Header .......................................................... 9**
Unit Code Field ................................................. 9**
Command Code Field .............................................. 9**
Status Field .................................................... 9**
Device Driver Functions ................................................. 9**
INIT ............................................................ 9**
MEDIA CHECK ..................................................... 9**
Media Descriptor Byte ........................................... 9**
BUILD BPB (BIOS Parameter Block) ................................ 9**
INPUT OR OUTPUT ................................................. 9**
NONDESTRUCTIVE INPUT NO WAIT .................................... 9**
STATUS .......................................................... 9**
FLUSH ........................................................... 9**
OPEN or CLOSE (DOS 3.0+) ........................................ 9**
REMOVEABLE MEDIA (DOS 3.0+) ..................................... 9**
The CLOCK$ Device ....................................................... 9**
DEVICE DRIVER FORMAT쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
A device driver is a handler for communication between the system software
and hardware devices. The motherboard ROM and IBMBIO.COM or IO.SYS files
contain the basic drivers for allowing DOS to talk to the console, disk drives,
serial and parallel ports, clock, and other resources.
DOS has five builtin drivers, STDIN, STDOUT, STERR, STDPRN, or STDAUX. An
"installable" driver may be loaded in the CONFIG.SYS file, and either replace
one of the builtin drivers or define a new resource, such as a mouse or
expanded memory driver.
The device driver is a COM (memory image) file that contains all of the code
needed to control an add-in device. An EXE file should not be used since the
EXE loader in some DOS 2.x versions is part of COMMAND.COM, which is not
present when the device driver is being loaded by IBMBIO.COM or IO.SYS. EXE
format drivers could be used in DOS 3.x+, but there is generally no reason to
do so. The COM file must not load at the usual ORG 100h. Since the driver does
not use the Program Segment Prefix, it is simply loaded without offset,
therefore the driver file must have an origin of 0. Most references advise
"ORG 0 or no ORG statement", however with the advent of many new assemblers on
the market, some of which default to .COM files, specifically stating "ORG 0"
may eliminate problems. Driver files should not have a declared stack segment.
DOS can install the device driver anywhere in memory, so care must be taken
in any FAR memory references. You should not expect that your driver will be
loaded in the same place every time.
TYPES OF DEVICES쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
There are two types of devices: Character devices and Block devices. Their
attributes are as follows:
Character devices are designed to do serial I/O in a byte-by-byte manner.
These devices have names like CON, AUX, or PRN, and you can open channels
(handles or FCBs) to do I/O much like a disk file. I/O may be in either cooked
or raw mode. (see Chapter 7 for discussion of cooked and raw modes). Because
character devices have only one name, they can only support one device.
Block devices are normally implemented as disk drives. They can do random I/O
in pieces called blocks, which are usually the physical sector size of the disk.
These devices are not named as character devices are, and cannot be opened
directly. Instead they are accessed by using drive letters such as A, B, C,
etc. Block devices can have units within them. In this way, a single block
driver can be responsible for one or more disk drives. For example, the first
block device driver can be responsible for drives A, B, C, and D. This means it
has four units defined and therefore takes up four drive letters. The position
of the driver in the chain of all drives determines the way in which the drive
letters correspond, i.e, if a second block device driver defines three units,
then those units are E, F, and G.
DOS 1.x allows 16 block devices. DOS 2.x allows 63, and DOS 3.x allows 26. It
is recommended that drivers limit themselves to 26 devices for compatibility
with DOS 3.x and 4.x. When DOS 2.x passes the Z: drivespec, the drivespecs get
a little wierd, such as ^, [, or #. DOS 3.x+ will return an error message.
CREATING A DEVICE DRIVER쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
To create a device driver that DOS can install, you must do the following:
1) Create a memory image (COM) file with a device header at the start of the
file.
2) Originate the code (including the device header) at 0, instead of 100h.
3) Set the next device header field. Refer to "Pointer to Next Device Header
Attribute Field" for more information.
4) Set the attribute field of the device header. Refer to "Attribute Field" for
more information.
5) Set the entry points for the interrupt and strategy routines.
6) Fill in the name/unit field with the name of the character device or the
unit number of the block device.
DOS always processes installable character device drivers before handling the
default devices. So to install a new CON device, simply name the device CON.
Be sure to set the standard input device and standard output device bits in
the attribute field of a new CON device. The scan of the device list stops on
the first match so the installable device driver takes precedence. For
instance, installing ANSI.SYS replaces the builtin CON driver.
DOS doesn't care about the position of installed character devices versus
block devices.
STRUCTURE OF A DEVICE DRIVER쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
A device driver consists of three major parts:
a device header
a strategy routine
an interrupt routine
DEVICE HEADER
The driver has a special header to identify it as a device and to define the
strategy and interrupt entry points and its various attributes. This header is
located at the beginning of the file. It contains a pointer to the next driver
in the chain, the attributes of the device, offsets into the strategy and
interrupt routines, and the device ID.
This is the format of the device header:
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� D E V I C E H E A D E R �
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쿚ffset � Length � Description �
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� 00h � word � Pointer to next device header field, offset value �
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� 02h � word � Pointer to next device header field, segment value �
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� 04h � word � Attribute �
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� 06h � word � Pointer to device strategy routine (offset only) �
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� 08h � word � Pointer to device interrupt routine (offset only) �
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� 0Ah �8 bytes � Name/Unit field �
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POINTER TO NEXT DEVICE HEADER FIELD
The device header field is a pointer to the device header of the next device
driver. It is a doubleword field that is set by DOS at the time the device
driver is loaded. The first word is the offset and the second word is the
segment.
If you are loading only one device driver, set the device header field to -1
before loading the device. If you are loading more than one device driver, set
the first word of the device driver header to the offset of the next device
driver's header. Set the device driver header field of the last device driver
to -1.
ATTRIBUTE FIELD
The attribute field is a word field used to identify the type of device this
driver is responsible for. This field distinguishes between block and
character devices and determines is selected devices are given special
treatment. The attributes are:
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� A T T R I B U T E F I E L D �
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� word � attr. � �
쳐컴컴컴컴컵컴컴컴캑 description �
� bits � set � �
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� 0 � 0 � not current standard input device �
� � 1 � current standard input device �
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� 1 � 0 � not current standard output device �
� � 1 � current standard output device �
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� 2 � 0 � not current NUL device �
� � 1 � current NUL device �
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� 3 � 0 � not current CLOCK device �
� � 1 � current CLOCK device �
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� 4 � 0 � standard CON I/O routines should be used �
� � 1 � fast screen I/O (int 29h) should be used �
쳐컴컴컴컴컵컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 5 - 10 � "reserved for DOS" - unknown - should be set to 0 �
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� 11 � 0 � doesn't support removeable media (default for DOS 2.x) �
� � 1 � supports removeable media (DOS 3.0+ only) �
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� 12 � "reserved for DOS" - unknown - should be set to 0 �
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� 13 � 0 � IBM format (block devices) �
� � 1 � non-IBM format (block devices) �
� � 1 � output till busy (character devices) �
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� 14 � 0 � doesn't support IOCTL �
� � 1 � supports IOCTL �
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� 15 � 0 � block device �
� � 1 � character device �
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note 1) If a bit in the attribute word is defined only for one type of device,
a driver for the other type of device must set that bit to 0.
2) For DOS 2.0 bits 4-12 must be off.
BIT 1 is the standard input and output bit. It is used for character devices
only. Use this bit to tell DOS if your character device driver is the
new standard input device or standard output device.
BIT 2 is the NUL attribute bit. It is used for character devices only. Use it
to tell DOS if your character device driver is a NUL device. Although
there is a NUL device attribute bit, you cannot reassign the NUL
device or replace it with your own routine. This attribute exists for
DOS so that DOS can tell if the NUL device is being used.
BIT 3 is the clock device bit. It is used for character devices only. Default
is 0. You can use it to tell DOS if your character device driver is the
new CLOCK device.
BIT 4 is the "fast video output" bit. The default is 0, which uses the BIOS
for writing to the screen. When set, this bit uses int 29h for much
faster screen updates.
BITS 5-10 reserved for DOS, unknown. Should be set to 0.
BIT 11 is the open/close removeable media bit. Use it to tell DOS if the
device driver can handle removeable media. This bit is valid for DOS
3.0+ only. This bit was reserved in DOS 2.x. Since DOS 2.x does not
look at this bit, its use is backward compatible.
BIT 12 reserved for DOS, unknown. Should be set to 0.
BIT 13 is the non-IBM format bit. When used for block devices it affects the
operation of the BUILD BPB (BIOS parameter block) device call. For
character devices it indicates that the devices implements the OUTPUT
UNTIL BUSY device call.
BIT 14 is the IOCTL bit. It is used for both character and block devices. Use
it to tell DOS whether the device driver can handle control strings
through the IOCTL function call 44h.
If a device driver cannot process control strings, it should set bit
14 to 0. This way DOS can return an error if an attempt is made through
the IOCTL function call to send or receive control strings to the
device. If a device can process control strings, it should set bit 14
to 1. This way, DOS makes calls to the IOCTL input and output device
function to send and receive IOCTL strings.
The IOCTL functions allow data to be sent to and from the device
without actually doing a normal read or write. In this way, the device
driver can use the data for its own use, (for example, setting a baud
rate or stop bits, changing form lengths, etc.) It is up to the device
to interpret the information that is passed to it, but the information
must not be treated as a normal I/O request.
BIT 15 is the device type bit. Use it to tell the system the that driver is a
block or character device.
POINTER TO STRATEGY ROUTINE
This field contains a pointer to "device strategy" function in the driver.
This function is called whenever a request is made to the driver, and must
store the location of the request header from DOS. This pointer is a word
value, and so must be in the same segment as the device header.
POINTER TO INTERRUPT ROUTINE
This field contains a pointer to the function which activates driver routines
to perform the command in the current request header. This is called by DOS
after the call to the strategy function, and should reset to the request header
address stored by "strategy", to allow for the possibility of interrupts
between the two calls. This pointer is a word value, and so must be in the same
segment as the device header.
NAME/UNIT FIELD
This is an 8-byte field that contains the name of a character device or the
number of units in a block device. For the character names, the name is
left-justified and the space is filled to 8 bytes. For block devices, the
number of units can be placed in the first byte. This is optional because DOS
fills in this location with the value returned by the driver's INIT code. The
other 7 bytes of the block device ID are reserved and should not be used.
INSTALLING DEVICE DRIVERS쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
DOS installs new device drivers dynamically at boot time by reading and
processing the DEVICE command in the CONFIG.SYS file. For example, if you have
written a device driver called RAMDISK, to install it put this command in the
CONFIG.SYS file:
DEVICE=[drive][path] RAMDISK [parameters]
DOS makes a FAR call to the device driver at its strategy entry point first,
using the request header to pass information describing what DOS wants the
device driver to do.
This strategy routine does not perform the request but rather queues the
request or saves a pointer to the request header. The second entry point is
the interrupt routine and is called by DOS immediately after the strategy
routine returns. The interrupt routine is called with no parameters. Its
function is to perform the operation based on the queued request and set up
any return infromation.
DOS passes the pointer to the request header in ES:BX. This structure consists
of a fixed length header (Request Header) followed by data pertinent to the
operation to be performed.
NOTE: It is the responsibility of the device driver to preserve the machine
state. For example, save all registers on entry and restore them on exit.
The stack used by DOS has enough room on it to save all the registers. If more
stack space is needed, it is the device driver's responsibility to allocate and
maintain another stack.
All calls to execute device drivers are FAR calls. FAR returns should be
executed to return to DOS.
INSTALLING CHARACTER DEVICES
One of the functions defined for each device is INIT. This routine is called
only once when the device is installed and never again. The INIT routine returns
the following:
A) A location to the first free byte of memory after the device driver, like a
TSR that is stored in the terminating address field. This way, the
initialization code can be used once and then thrown away to save space.
B) After setting the address field, a character device driver can set the status
word and return.
INSTALLING BLOCK DEVICES
Block devices are installed in the same way as character devices. The
difference is that block devices return additional information. Block devices
must also return:
A) The number of units in the block device. This number determines the logical
names the devices will have. For example, if the current logical device
letter is F at the time of the install call, and the block device driver INIT
routine returns three logical units, the letters G, H, and I are assigned to
the units. The mapping is determined by the position of the driver in the
device list and the number of units in the device. The number of units
returned by INIT overrides the value in the name/unit field of the device
header.
B) A pointer to a BPB (BIOS Parameter Block) pointer array. This is a pointer
to an array of "N" word pointers there "N" is the number of units defined.
These word pointers point to BPBs. This way, if all of the units are the
same, the entire array can point to the same BPB to save space.
The BPB contains information pertinent to the devices such as the sector
size, number of sectors per allocation unit, and so forth. The sector size of
the BPB cannot be greater than the maximum allotted size set at DOS
initialization time. This array must be protected below the free pointer set
by the return.
C) The media descriptor byte. This byte is passed to devices so that they know
what parameters DOS is currently using for a particular drive unit.
Block devices can take several approaches. They can be "dumb" or "smart". A
dumb device would define a unit (and therefore a BPB) for each possible media
drive combination. Unit 0=drive 0;single side, unit 1=drive 0;double side, etc.
For this approach, the media descriptor bytes would mean nothing. A smart
device would allow multiple media per unit. In this case, the BPB table
returned at INIT must define space large enough to acommodate the largest
possible medias supported (sector size in BPB must be as large as maximum
sector size DOS is currently using). Smart drivers will use the media
descriptor byte to pass information about what media is currently in a unit.
REQUEST HEADER쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
The request header passes the information describing what DOS wants the
device driver to do.
When a valid device driver command code or function is called by your
application program, DOS develops a data structure called the "Request Header"
in ES:BX and passes it to the strategy entry point. This structure consists of
a 13-byte defined header which may be followed by other data bytes depending on
the function requested.
It is the device driver's responsibility to preserve the machine state, for
example, saving all registers including flags on entry and restoring them on
exit. There is enough room on the stack when strategy or interrupt is called
to do about 20 pushes. If more stack is needed, the driver should set aside
its own stack space.
The fixed ("static") part of the request header is as follows:
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� R E Q U E S T H E A D E R �
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쿚ffset 쿗ength � F i e l d �
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� 00h � byte � Length in bytes of the request header plus any data at end �
쳐컴컴컴탠컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 01h � byte � Unit code. Determines subunit to use in block devices �
� � � (minor device) Has no meaning for character devices �
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� 02h � byte � Command code �
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� 03h � word � Status �
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� 05h �8 bytes� Reserved for DOS �
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� 0Ch 퀆aries � Data appropriate for the operation �
읕컴컴컴좔컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
REQUEST HEADER LENGTH FIELD
The length in bytes of the total request header (0-255) plus any data at the
end of the header.
UNIT CODE FIELD
The unit code field identifies which unit in a block device driver the request
is for. For example, if a block device driver has three units defined, then the
possible values of the unit code field would be 0, 1, and 2. This field is not
valid for character devices.
COMMAND CODE FIELD
The command code invokes a specific device driver function. Functions 0
through 12 are supported in all device drivers. Functions 13-15 are available
only in DOS 3.0 or higher. Some functions are relevant for either character or
block devices but not both; nonetheless all functions must have an executable
routine present even if it does nothing but set the done flag in the return
status word in the request header.
The command code field in the request header can have the following values:
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� code � name � function �
쳐컴컴컵컴컴컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� 0 � INIT � initialize driver for later use (used once only) �
� 1 � MEDIA CHECK � block devices only, NOP for character devices �
� 2 � BUILD BPB � block devices only, NOP for character devices �
� 3 � IOCTL input � called only if device has IOCTL bit set �
� 4 � INPUT � read data �
� 5 � NONDESTRUCTIVE INPUT NO WAIT character devices only �
� 6 � INPUT STATUS � character devices only �
� 7 � INPUT FLUSH � character devices only �
� 8 � OUTPUT � write data �
� 9 � OUTPUT � write data with verify �
� 10 � OUTPUT STATUS � character devices only �
� 11 � OUTPUT FLUSH � character devices only �
� 12 � IOCTL OUTPUT � called only if device has IOCTL bit is set �
� 13 � DEVICE OPEN � called only if OPEN/CLOSE/RM bit is set �
� 14 � DEVICE CLOSE � called only if OPEN/CLOSE/RM bit is set �
� 15 � REMOVEABLE MEDIA � only if OPEN/CLOSE/RM bit set & device is block �
� 16 � OUTPUT UNTIL BUSY� only called if bit 13 is set & device is character �
읕컴컴컨컴컴컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
The individual command codes are described later in this chapter.
STATUS FIELD
The status word field is zero on entry and is set by the driver interrupt
routine on return.
The status field in the request header contains:
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� D E V I C E D R I V E R S T A T U S F I E L D �
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� size 쿫it� definition �
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� byte � 0 � �
� � 1 � �
� � 2 � �
� � 3 � Error message return code �
� � 4 � (with bit 15=1) �
� � 5 � �
� � 6 � �
� � 7 � �
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� byte � 8 � DONE �
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� � 9 � BUSY �
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� � A � Reserved by DOS, unknown �
� � B � �
� � C � �
� � D � �
� � E � �
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� � F � Error �
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The low 8 bits of the status word define an error message if bit 15 is set.
These errors are:
00h write protect violation 01h unknown unit
02h device not ready 03h unknown command
04h CRC error 05h bad drive request structure length
06h seek error 07h unknown media
08h sector not found 09h printer out of paper
0Ah write fault 0Bh read fault
0Ch general failure 0Dh reserved
0Eh reserved 0Fh invalid disk change
BIT 8 is the done bit. If it is set, it means the operation is complete. The
driver sets the bit to 1 when it exits.
BIT 9 is the busy bit. It is only set by status calls and the removable media
call.
BITS 10-14 are reserved.
BIT 15 is the error bit. If this bit is set, the low 8 bits of the status word
(7-0) indicate the error code.
RESERVED FOR DOS
Official sources label this area as "reserved for DOS". Another source
indicates that this consists of two double-word (4-byte) pointers to be used
to maintain a linked list of request headers for this device and a list of all
current device requests being processed by DOS. This was apparently to be used
for the undelivered multitasking version of DOS.
DEVICE DRIVER FUNCTIONS쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
All strategy routines are called with ES:BX pointing to the request header.
The interrupt routines get the pointers to the request header from the queue
the strategy routines stores them in. The command code in the request header
tells the driver which function to perform.
NOTE: All DWORD pointers are stored offset first, then segment.
############################
INIT
Command code = 0 (all devices)
Performs all initialization required at DOS boot time to install the
driver and set local driver variables. This function is called only
once, when the driver is loaded.
ES:BX pointer to 26-byte request header and data structure
Format of structure:
offset length field
00h 13 bytes request header
0Dh byte number of units (not set by character devices)
11h dword ending address of the driver's resident code
15h dword pointer to BPB array (not set by character devices)
/pointer to remainder of arguments
19h byte drive number (DOS 3.0+ only)
When INIT is called, the driver must do the following:
A) set the number of units (block devices only)
B) set up the pointer to the BPB array (block devices only)
C) perform any initialization code (to modems, printers, etc)
D) set the ending address of the resident program code
E) set the status word in the request header
To obtain information obtained from CONFIG.SYS to a device driver at INIT
time, the BPB pointer field points to a buffer containing the information
passed from CONFIG.SYS following the =. The buffer that DOS passes to the
driver at INIT after the file specification contains an ASCII string for the
file OPEN. The ASCII string (ending in 0h) is terminated by a carriage return
(0Dh) and linefeed (0Ah). If there is no parameter information after the file
specification, the file specification is immediately followed by a linefeed
(0Ah).
NOTE: This information is read-only and only system calls 01h-0Ch and 30h can
be issued by the INIT code of the driver.
The last byte parameter contains the drive letter for the first unit of a
block driver. For example, 0=A, 1=B etc.
If an INIT routine determines that it cannot set up the device and wants to
abort without using any memory, follow this procedure:
A) set the number of units to 0
B) set the ending offset address at 0
C) set the ending offsret segment address to the code segment (CS)
NOTE: If there are multiple device drivers in a single memory image file, the
ending address returned by the last INIT called is the one DOS uses. It is
recommended that all device drivers in a single memory image file return
the same ending address.
############################
MEDIA CHECK
command code = 1 (block devices only)
Checks to see if disk had been changed since last access.
ES:BX pointer to 19-byte request header and data structure
Format of structure:
offset length field
00h 13 bytes request header
0Dh byte media descriptor from BPB
0Eh byte returned
0Fh dword returns a pointer to the previous volume ID (if bit
11=1 and disk change is returned) (DOS 3.0+)
When the command code field is 1, DOS calls MEDIA CHECK for a drive unit and
passes its current media descriptor byte. See "Media Descriptor Byte" later in
this chapter for more information about the byte. MEDIA CHECK returns one of
the following:
A) media not changed C) not sure
B) media changed D) error code
The driver must perform the following:
A) set the status word in the request header
B) set the return byte
00h don't know if media has been changed
01h media has not been changed
-1 media has been changed
DOS 3.0+: If the driver has set the removable media bit 11 of the device header
attribute word to 1 and the driver returns -1 (media changed), the driver must
set the DWORD pointer to the previous volume identification field. If DOS
determines that the media changed is an error, DOS generates an error 0Fh
(invalid disk change) on behalf of the device. If the driver does not implement
volume identification support, but has bit 11 set to 1, the driver should set a
pointer to the string "NO NAME",0.
MEDIA DESCRIPTOR
Currently the media descriptor byte has been defined for a few media types.
This byte should be identical to the media byte if the device has the non-IBM
format bit off. These predetermined values are:
media descriptor byte => 1 1 1 1 1 0 0 0
(numeric order) 7 6 5 4 3 2 1 0
BIT MEANING
0 0 not double sided
1 double sided
1 0 not 8 sector
1 8 sector
2 0 nonremoveable
1 removeable
3-7 must be set to 1
############################
BUILD BPB (BIOS Parameter Block)
command code = 2 (block devices only)
ES:BX pointer to 22-byte request header and data structure
Format of structure:
offset length field
00h 13 bytes request header
0Dh byte media descriptor from DOS
0Eh dword transfer address (buffer address)
12h dword pointer to BPB table
DOS calls BUILD BPB under the following two conditions:
A) If "media changed" is returned.
B) If "not sure" is returned. If so, there are no used buffers. Used buffers
are buffers with changed data that have not yet been written to the disk.
The driver must do the following:
A) set the pointer to the BPB.
B) set the status word in the request header.
The driver must determine the correct media type currently in the unit to
return the pointer to the BPB table. The way the buffer is used (pointer
passed by DOS) is determined by the non-IBM format bit in the attribute field
of the device header. If bit 13=0 (device is IBM compatible), the buffer
contains the first sector of the FAT (most importantly the FAT ID byte). The
driver must not alter this buffer in this case. If bit 13=1 the buffer is a
one sector scratch area which can be used for anything.
For drivers that support volume identification and disk change, the call
should cause a new volume identification to be read off the disk. This call
indicates that the disk has been legally changed.
If the device is IBM compatible, it must be true that the first sector of the
first FAT is located at the same sector for all possible media. This is
because the FAT sector is read before the media is actually determined.
The information relating to the BPB for a particular media is kept in the boot
sector for the media. In particular, the format of the boot sector is:
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� For DOS 2.x, 3 byte near jump (0E9h) For DOS 3.x+, 2 byte near jump (0EBh) �
� followed by a NOP (90h) �
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� 8 bytes � OEM name and version �
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� BYTE � � sectors per allocation unit (must be a power of 2) �
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� WORD � B � reserved sectors (strarting at logical sector 0) �
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� BYTE � � number of FATs �
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� WORD � P � max number of root directory entries �
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� WORD � � number of sectors in logical image (total number of �
� � � sectors in media, including boot sector directories, etc.) �
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� BYTE � � media descriptor �
쳐컴컴컴컴캑 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� WORD � � number of sectors occupied by a single FAT �
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� WORD � sectors per track �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� WORD � number of heads �
쳐컴컴컴컴컵컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑
� WORD � number of hidden sectors �
읕컴컴컴컴컨컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸
The three words at the end return information about the media. The number of
heads is useful for supporting different multihead drives that have the same
storage capacity but a different number of surfaces. The number of hidden
sectors is useful for drive partitioning schemes.
############################
INPUT / OUTPUT (IOCTL)
command code = 3 IOCTL Read
4 Read (block or character devices)
8 Write (block or character devices)
9 Write With Verify
12 IOCTL Write
16 Output Until Busy (character devices only)
ES:BX pointer to 24-byte request header and data structure
Format of structure:
offset length field
00h 13 bytes request header
0Dh byte media descriptor byte from BPB
0Eh dword transfer address (buffer address)
12h word byte/sector count
14h word starting sector number (block devices)
[no meaning on character devices]
16h dword (DOS 3.0+) pointer to the volume ID if error code
0Fh is returned
The driver must perform the following:
A) set the status word in the request header
B) perform the requested function
C) set the actual number of sectors or bytes tranferred
No error checking is performed on an IOCTL I/O call. However, the driver must
set the return sector or byte count to the actual number of bytes transferred.
Under certain circumstances a block device driver may be asked to do a write
operation of 64k bytes that seems to be a "wrap around" of the transfer address
in the BIOS I/O packet. This arises due to an optimization added to write code
in DOS. It will only happen in writes that are within a sector size of 64k on
files that are being extended past the current end of file. It is allowable for
the device driver to ignore the balance of the write that wraps around, if it
so chooses. For example, a write of 10000h bytes worth of sectors with a
transfer address of XXX:1 ignores the last two bytes. A user program can never
request an I/O of more than 0FFFFh bytes and cannot wrap around (even to 0) in
the transfer segment, so in that case the last two bytes can be ignored.
A program that uses DOS function calls can never request an input or output
function of more than 0FFFFh bytes, therefore, a wrap around in the transfer
(buffer) segment can never occur. It is for this reason you can ignore bytes
that would have wrapped around in the tranfer segment.
If the driver returns an error code of 0Fh (invalid disk change) it must put
a DWORD pointer to an ASCIIZ string which is the correct volume ID to ask the
user to reinsert the disk.
DOS 3.0+:
The reference count of open files on the field (maintained by the OPEN and
CLOSE calls) allows the driver to determine when to return error 0Fh. If there
are no open files (reference count=0) and the disk has been changed, the I/O
is all right, and error 0Fh is not returned. If there are open files
(reference count > 0) and the disk has been changed, an error 0Fh condition
may exist.
############################
NONDESTRUCTIVE INPUT NO WAIT
command code = 5 (character devices only)
Reads a character from input stream but does not remove it from the
buffer
ES:BX pointer to 14-byte request header and data structure
Format of structure:
offset length field
00h 13 bytes request header
0Dh byte read from device
The driver must do the following:
A) return a byte from the device
B) set the status word in the request header.
If the character device returns busy bit=0 (characters in the buffer), then
the next character that would be read is returned. This character is not removed
form the buffer (hence the term nondestructive input). This call allows DOS to
look ahead one character.
############################
STATUS
command codes = 6 Input Status (character devices only)
10 Output Status (character devices only)
Check for characters waiting in input buffer
ES:BX pointer to 13-byte request header
This driver must perform the following:
A) perform the requested function
B) set the busy bit
C) set the status word in the request header.
The busy bit is set as follows:
For input on unbuffered character devices: if the busy bit (bit 9) is 1 on
return, a write request would wait for completion of a current request. If the
busy bit is 0, there is no current request. Therefore, a write request would
start immediately.
For input on buffered character devices: if the busy bit is 1 on return, a
read request does to the physical device. If the busy bit is 0, there are
characters in the device buffer and a read returns quickly. It also indicates
that a user has typed something. DOS assumes all character devices have a type-
ahead input buffer. Devices that do not have this buffer should always return
busy=0 so that DOS does not hang waiting for information to be put in a buffer
that does not exist.
############################
FLUSH INPUT BUFFERS
command code = 7 (character devices only)
Forces all data in buffers to specified device.
ES:BX pointer to 13-byte request header
This call tells the driver to flush (terminate) all pending requests that it
has knowledge of. Its primary use is to flush the input queue on character
devices.
The driver must set the status word in the request header upon return.
############################
FLUSH OUTPUT BUFFERS
command code 11 (character devices only)
Forces all data in buffers to specified device.
ES:BX pointer to 13-byte request header
This call tells the driver to flush all output buffers and discards any
pending requests. Its primary use is to flush the output queue on character
devices.
The driver must set the status word in the request header upon return.
############################
OPEN or CLOSE (DOS 3.0+)
command code = 13 Open (block or character devices)
14 Close (block or character devices)
ES:BX pointer to 13-byte static request header
These calls are designed to give the device information about the current file
activity on the device if bit 11 of the attribute word is set. On block
devices, these calls can be used to manage local buffering. The device can keep
a reference count. Every OPEN causes the device to increment the reference
count. Every CLOSE causes the device to decrement the reference count. When the
reference count is 0, if means there are no open files in the device. Therefore,
the device should flush buffers inside the device it has written to because now
the user can change the media on a removeable media drive. If the media had been
changed, it is advisable to reset the reference count to 0 without flushing the
buffers. This can be thought of as "last close causes flush". These calls are
more useful on character devices. The OPEN call can be used to send a device
initialization string. On a printer, this could cause a string to be sent to set
the font, page size, etc. so that the printer would always be in a known state
in the I/O stream. Similarly, a CLOSE call can be used to send a post string
(like a form feed) at the end of an I/O stream. Using IOCTL to set these pre and
post strings provides a flexible mechanism of serial I/O device stream control.
Since all processes have access to STDIN, STDOUT, STDERR, STDAUX, and STDPRN
(handles 0, 1, 2, 3, and 4) the CON, AUX, and PRN devices are always open.
############################
REMOVABLE MEDIA (DOS 3.0+)
command code = 15 (block devices only)
This call identifies the media type as removable or nonremovable.
ES:BX pointer to 13-byte static request header
To use this call, set bit 11 (removable media) of the attribute field to 1.
Block devices can only use this call through a subfunction of the IOCTL
function call (int 21h fn44h).
This call is useful because it allows a utility to know whether it is dealing
with a nonremovable media drive or with a removable media drive. For example,
the FORMAT utility needs to know whether a drive is removable or nonremovable
because it prints different versions of some prompts.
note No error checking is performed. It is assumed that this call always
succeeds.
THE CLOCK$ DEVICE쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
To allow a clock board to be integrated into the system for TIME and DATE,
the CLOCK$ device is used. This device defines and performs functions like any
other character device (most functions will be reset done bit, reset error bit,
and return). When a read or write to this device occurs, 6 bytes are
transferred. The first 2 bytes are a word, which is the count of days since
01-01-80. The third byte is minutes, the fourth is hours, the fifth is
hundredths of a second, and the sixth is seconds.
Reading the CLOCK$ device gets the date and time, writing to it sets the date
and time. CLOCK$ is normally called only when the system is initializing or if
the system time and date are set (DOS 3.3+). DOS carries the system time and
date internally after receiving it from the CLOCK$ driver.
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
C R E D I T S
The information presented here was gathered from megabytes of files found on
BBS systems, conversations on a dozen different BBS systems, correspondence,
and every reference book I could get my hands on. On occasion, a number of
prestigious references didn't agree with each other. Where this has happened, I
have used the latest references. There is too much information here for me to
verify every fact personally. I have used my own judgement as to the
reliability of the sources.
I've been selling copies of the Reference since October 1987. The original
basis for the Reference came from Peter Norton's "Programmer's Guide to the
IBM PC" and the original Janet Jack interrupt list circa sometime 1986, as
updated by Ross Greenberg. Anyway, I've prepared a list of the sources I've
used for the Reference to clear up any ambiguities.
Tools used in preparing this book:
Microsoft SymDeb, the final gasp of venerable DEBUG.COM and a fine program.
Microsoft CodeView, huge and awkward though it may be.
V Communications Sourcer, the only effective disassembler I've found.
References used in preparing this book:
AST EEMS Technical Reference Manual v3.2
documents 020022-001B and 000408-001B
provided by AST Corporation, 1987
AT&T 6300 Plus Hardware Reference Manual
p/n 999-300-194IS
from AT&T Corp, 1985 (before the Death Star logo, yet...)
Creative Labs Sound Blaster User Reference Manual
copr. 1989
Data General Programmer's Reference for MS-DOS, Rev.3
Data General Corporation (covers through DOS 3.0)
p/n 069-100157 rev 00 May 1986
Digital Research DR-DOS System and Programmer's Guide v3.32
Digital Research Corporation 1988
comment: This manual does not cover the extended disk partition access,
file password protection, or any of the other goodies
provided in DR-DOS. In fact, it not only doesn't cover the
extended features, it doesn't completely cover DOS calls
documented by IBM. It does have an extensive section on
customizing DR-DOS for use from ROM.
Digital Research DR-DOS User's Guide v3.32
Digital Research Corporation 1988
Digital Research DR-DOS Reference Guide v3.32
Digital Research Corporation 1988
Digital Research DR-DOS Users and Reference Guide v3.40
Digital Research Corporation, January 1989
Digital Research DR Multiuser DOS Users and Reference Guide v5.0
Digital Research Corporation, 1991
Digital Research DR-DOS Users and Reference Guide v5.0
Digital Research Corporation, 1991
DPMI 0.9 Specification
Intel Corp, 1990
DPMI 1.0 Specification
Intel Corp, 1991
An Introduction to the DOS Protected Mode Interface
Software Focus Group
Intel Corp, March 1991 order # 240787-002
IBM DOS Operations Manual Version 2.00
IBM Corp, 1983
IBM DOS Operations Manual Version 2.10
IBM Corp, 1983
IBM DOS Operations Manual Version 3.1
IBM Corp, November 1984
IBM DOS Operations Manual Version 3.3
IBM Corp, April 1987
IBM DOS Technical Reference, Version 4.0
IBM Corp, 1988
IBM DOS Command Reference, Version 4.0
p/n 6280254
IBM Corp, 1988
IBM PC Local Area Network Program Version 1.20
IBM Corp, April 1987
IBM Technical Reference
Options and Adapters - Enhanced Graphics Adapter
p/n 6280131 IBM Publications Aug 1984
IBM Technical Reference
Personal Computer
p/n 6322507 IBM Publications
IBM Technical Reference
Personal Computer - PCjr
p/n 1502293 IBM Publications
LANtastic Programmer's Information Package, 2/21/89
Logitech Mouse Programmer's Toolkit
Logitech Corp. 1986
Lotus-Intel-Microsoft Expanded Memory Specification Version 3.20
part number 300275-003
provided by Intel Corp. September, 1985
Lotus-Intel-Microsoft Expanded Memory Specification 4.0
document 300275-005
provided by Intel Corp. October 1987
Lotus-Intel-Microsoft Expanded Memory Specification 4.0
EMS Toolkit for C Developers
document 302243-001
provided by Intel Corp, February 1990
Microsoft - various documents provided to MS 5.0 beta testers
Microsoft Extended Memory Specification v2.00
provided by Microsoft Corporation, 1988
Microsoft Mouse Technical Reference
Microsoft Press, 1989
Mouse Systems Programmer's Toolkit
p/n 302449-001 Rev A, 1989
p/n 302375-100, 1989
p/n 302446-100, 1989
MS-DOS Programmer's Reference (covers through DOS 2.00)
by Microsoft
p/n 135555-001 Intel Corp. 1984
MS-DOS 5.0 Programmer's Reference (covers DOS 5.0 only)
by Microsoft
Microsoft Press 1991, ISBN 1-55615-329-5
Phar Lap Virtual Control Program Interface (VCPI) Specification v1.0
Phar Lap Software 1989
Tandy 1000 TX Technical Reference Manual
Tandy Corp.
p/n 25-1514 Tandy Corp 1987
The Software Link
PC-MOS 4.1 Programmer's Reference
Toshiba 1000 Technical Reference Manual
Toshiba Corp. of America 1987
Tseng Labs EVA Chipset Programming Guide
Tseng Labs, 1986
X3.4-1977: American National Standard Code for Information Interchange
by American National Standards Institute (ANSI)
New York, NY 1977
Weitek ABACUS Software Designer's Guide, Doc 8967
September 1989
Wendin, Inc
Wendin-DOS Programmer's Reference
**********************
ATI EGA Wonder Operation Manual
ATI Technologies, 1987
Everex EV-650 EGA Reference Guide, Version 1.00
Everex Computer, 1986
FastCard IV User Manual
Peripheral Marketing Inc.
p/n 0527 Jan 1987
Hercules Graphics Card User's Manual
Hercules Computer Technology
1983
Hercules Graphics Card Plus Owner's Manual
Hercules Computer Technology
Model GB112 1987
JDR B-3101 FLoppy Disk Drive Card User's Guide
470.03002 version 1.00 1988
LANtastic 2.46 Installation Guide
Artisoft, 1988
LANtastic 3.01 Installation Guide
Artisoft, 1990
LANtastic 4.0 beta Installation Guide
Artisoft, 1991
LapLink Release 2 User's Manual
Traveling Software, 1987
LapLink Release 3 User's Manual
Traveling Software, 1989
Logitech EGA Reference Manual, EGA+Mouse Board
Mirage Super VGA TVGA-8900 User's Manual
MPC Operations Guide, Manual #1023
Columbia Data Products, Inc.
CDP 1983
Microcomputer Products - 1987 Data Book
NEC Electronics, Inc.
p/n 500105 Aug 1987
NEC uPD70108/70116 Microprocessor User's Manual
p/n 500350 October 1986
provided by NEC Electronics, Inc.
Novell Advanced Netware System Manager's Reference
pcAnywhere User's Guide v2.00
Dynamic Microprocessor Associates, Inc 1986
S-286 User Manual, version 2
Link Computer, 1988
STB VGA Extra/EM
EM-16 BIOS Features
STB Corp.
TesSeRact v1.0 documentation
TCXL 5.1 documentation
Toshiba ND352/356 3.5" Diskette Drive Installation Notes
document number 87019 March 1988
Toshiba America Corporation
Tseng Labs
EVA, EVA/480 BIOS Guide
November 10, 1988
VESA Toolkit v2.0
summer 1991
VideoTrax Installation Guide
Alpha Micro, 1987
******************
Advanced MSDOS
Ray Duncan
Microsoft Press 1986
Assembly Language Programming for the IBM Personal Computer
David J. Bradley
Prentice-Hall 1984
Assembly Language Subroutines for MSDOS Computers
Leo J. Scanlon
TAB Books 1986
Atari ST Internals
Gerits, English, & Bruckmann
Abacus Software 1985
Compute!'s Guide to Assembly Language Programming on the IBM PC
COMPUTE! Publications
Compute!'s Mapping the IBM PC and PCjr
Russ Davis
COMPUTE! Publications
DOS Power Tools
Paul Somerson
Bantam Books 1988
DOS: The Complete Reference
Kris Jamsa
Osborne/McGraw-Hill 1987
Exploring the IBM PCjr
Peter Norton
Microsoft Press 1984
Discovering the IBM PCjr
Peter Norton
Microsoft Press 1984
IBM Video Subsystems
Richard Wilton
Microsoft Press 1988
Inside the IBM PC
Peter Norton
Mapping the IBM PC
Russ Davies/Compute! Magazine
Compute! Books 1986
Memory Resident Utilities, Interrupts, and Disk Management With MS & PC DOS
Michael Hyman
MIS Press 1987
Microcomputer Interfacing
Bruce A. Artwick
Prentice Hall 1980
Microsoft Systems Journal - March 1987
"Expanded Memory: Writing Programs that Break the 640k Barrier"
Marion Hansen, Bill Krueger, Nick Stuecklen
MS-DOS Encyclopedia
Ray Duncan
Microsoft Press 1988 (first edition)
Network Programming in C
Barry Nance (barryn on BIX)
Que, 1990
Operating Systems Design and Implementation
Arthur S. Tanenbaum
Prentice Hall 1987
Programmer's Guide to the IBM PC
Peter Norton
Microsoft Press 1985
Programmer's Problem Solver for the IBM PC, XT, & AT
Robert Jourdain
Prentice Hall 1986
Running MS-DOS
Van Wolverton
Microsoft Press
Supercharging MS-DOS
Van Volverton
Microsoft Press 1986
The 8080a Bugbook
Tony-Larsen-Titus
Howard W. Sams 1977
The 8086 Book
Russell Rector and George Alexy
Osborne/McGraw-Hill 1980
The IBM Personal Computer from the Inside Out
Murray Sargent III and Richard L. Shoemaker
Addison-Wesley 1984
The IBM ROM BIOS
Ray Duncan
Microsoft Press 1988
The Serious Assembler
Charles A. Crayne and Dian Gerard
Baen Books 1985
Tricks of the MS-DOS Masters
Waite Group
Howard W. Sams 1987
Turbo Pascal Express
Robert Jourdain
Brady Books, 1987
Writing DOS Device Drivers in C
Adams/Tondo
Prentice Hall, 1990
***********************
Microsoft Macro Assembler 4.0, 5.1 documentation
Microsoft C 4.0 documentation
Borland Turbo Pascal 3.02a and 5.0 documentation, Turbo C 2.0 documentation
Novell SFT System Administrator's Reference
***************************
Western Digital, Rodime, Miniscribe, Microscience, Adaptec, Storage
Technologies, and Connor Peripherals were kind enough to send spec sheets on
most of their products which helped to expand and verify the hard drive
information in Appendix 6.
***************************
A large amount of miscellaneous information came from various computer
magazines. Documenting what came from where would be an experience all its
own. A great deal of information came from articles by Michael Mefford and
Charles Petzold of PC Magazine, and Neil Rubenking, Jeff Duntemann, and
Ray Duncan, who get around a lot.
Byte
( Byte's kinda weird. They have some really neat, well-researched
stuff interspersed with mindless drivel. Still, they print some
stuff you absolutely, positively won't find anywhere else. )
C'T (Computer Technik)
( If you read German, this one is sorta like PC Magazine was in its
heyday. )
Computer Language
( I never decided if I liked CL or not. Maybe I'm not the sort of
programmer they're writing for... )
Computer Shopper
( Though primarily advertising, some information sneaks in from time
to time. )
Dr. Dobb's Journal
( I always thought the old title, "Doctor Dobbs' Journal of Computer
Calisthenics and Orthodontia - Running Light Without Overbyte" was
a killer name, but nobody asked me. )
InfoWorld
( I never really figured out how a weekly magazine could so often be
both late *and* wrong with their stories, but IW tries hard. Still,
you often hear about rumblings you'd never find out about in the
slicks. The National Enquirer of the computer world? )
Micro Cornucopia
( R.I.P - it was great while it lasted. )
Microsoft Systems Journal
( Hideously expensive and mostly oriented to Windows and OS/2, the
early issues had some really good stuff )
Midnight Engineering
( This one's hard to classify. It's hardcore computer with a dash
of entrepreneurship, bizarre as the combination may sound. I like
it when I can find it. )
PC Magazine
( Despite their new "management format" in mid '89, PC Mag still has
some good techie stuff from time to time. I guess the bean counters
thought managers were more important than programmers. )
PC Resource
( There was rarely anything of interest in PC Resource, but every
now and then I found something. Now defunct. )
PC Tech Journal
( "Tell 'em what you're going to say, tell 'em what you're saying, tell
'em what you just said." - and don't send us no steenking submissions
unless they're in WordPerfect format! Despite their fascist policies,
every now and then they printed something useful. The Little Rock
Wild Bunch refered to it as "PC Tech Urinal," an apt monicker. Now
defunct. )
PC Techniques
( This is the magazine PC Tech Journal tried to advertise itself as.
Pure programming, written by programmers for programmers, without
too many "journalists" pissing in the text. Try it! )
Programmer's Journal
( This is a nice magazine, though expensive. )
Tech Specialist
( One of the few really good magazines for bit-twiddlers. Haven't
seen a GUI phone-dialer shootout yet! )
****************************
various computer bulletin board systems, including
Byte Information Exchange (BIX)
(check out ibm.dos/old.secrets.2 and ibm.dos/secrets.3)
Effusive thanks to the gang in the ibm.exchange - these guys are *sharp*.
In alphabetic order:
barryn, billn, daiken, dgh, dmick, dnanian, dondumitru, drifkind, geary,
glass, gmussar, greenber, hfishman, j_vanderbilt, jdunlap, jlussmeyer, johnf,
jsloman, jsprowl, jswitzer, jrichards, mike123, rbabcock, rbrukardt, rduncan,
roedy, sjgrant, skluger, terjem, twagner, wardc, wcowley, and all the guys
whose names forgot...
Compuserve IBM SIG
FIDOnet international network (various technical echos)
GEnie IBM RT and Borland RT
PCanada BBS system (Toronto, Canada)
RIME PCRelay international network (IBM, Technical, Programming echos)
TelePath
*********************************
The following text files were of use. Bear in mind that some of them may be
seen under several different names. The author's name is given as it appears
in the documentation (if any).
10H-BUG ASM 4680 29/01/87 bug in 2.x int 21h/fn10h Ray Duncan
1PT4MB INF 5120 3/10/87 1.44Mb drives Clyde Washburn 70305,1211
2EH ASM 2969 3/03/87 info on undoc'd int 2Eh David Gwillim
386BUG ARC 9216 15/10/87 bug in early 80386 chips Compaq Corp.
8086 3 10572 5/12/88 dump of Fidonet?? 8086 conf??
8259 ARC 2826 15/03/88 info on 8259 chip
APICALLS ARC 11481 8/01/88 OS/2 API function call list Bill Earle
ASM-ADRS ARC 6144 20/12/87 low memory vectors Malcolm McCorquodale
ATCMDS ARC 3072 20/03/88 Hayes 1200 baud command set
BACKDOOR UPL 26115 11/12/89 "back door" through PSP John Switzer
BIOSDOC ARC 34816 3/11/87 very good function list David E. Powell
BIXDOS1 ARC 155648 14/12/87 BIX "MSDOS Secrets" #1
BUG40DOS ARC 3200 18/08/88 bugs in DOS 4.0 "Doug"
CAS ARC 33792 27/10/88 Communicating Applications Standard 1.0A
DCA, Intel Corp
CCPM86 ARC 68238 14/10/89 list of Concurrent CP/M calls
CDOS ARC 35584 18/07/89 list of Concurrent DOS calls Guy Scharf
CDOS2_ ARC 227200 18/07/89 list of Concurrent DOS calls J. F. Jankura
CDOSCALL ARC 19968 18/07/89 list of Concurrent DOS calls J. F. Jankura
CUFEXT ARC 13228 13/03/90 common file extensions J.W. Rider
DEBUGTUT ARC 15655 23/04/88 DEBUG tutorial
possibly David Whitman?
DIAGNOSE ARC 14336 1/01/86 memory errcodes Jerry Schneider, Arnold Kischi
DISK144 ARC 23086 16/10/88 info on 1.44Mb diskettes
DISKTYPE ARC 5073 14/04/88 IBM floppy formats
DOOM ARC 9216 29/09/88 hard drive information
DOS-SIZE ARC 787 27/03/88 size of DOS files 1.1-3.1
DOS3TXT ARX 9168 31/07/85 list of DOS/BIOS ints, data areas Dan Rollins
DOS32 ARC 17408 31/05/88 command list for DOS 3.2
DOS3BUGS ARC 5639 15/10/87 acknowledged bugs in DOS 3.0-3.2 IBM Corp.
DOS40 ARC 15625 22/07/88 IBM announcement of DOS 4.0 IBM Corp.
DOS401 ARC 18178 19/10/88 errors in DOS 4.0 IBM Corp.
DOS40B ARC 27008 26/08/88 Compuserve thread on DOS 4.0
DOS40FAT ARC 1510 11/09/88 DOS 4.0 File Allocation Table Mike Austin
DOS40FUN ZOO 3410 31/12/99 DOS 4.0 int 24, 25, etc Pat Myrto
DOS40HLP ARC 53376 28/08/88 DOS 4.0 command set
DOS40TXT ARC 46169 16/10/88 DOS 4.0 problems & info
DOS4TIPS ARC 1735 19/09/88 problems with DOS 4.0 IBM Corp.
DOSBUG TXT 1024 15/10/87 info on 2.0 volume label
DOSGUIDE ARC 21344 21/02/88 DOS tutorial Carrington B. Dixon
DOSINT ARC 4201 15/03/88 list of DOS 2.0 function calls John Chapman
DOSNOTES ARC 5052 15/03/88 info on DOS undoc fns.
DOSREF ARC 9216 21/01/87 partial list of PC BIOS calls
DOSREF ARC 62052 23/08/86 device driver info "Cracker"
DOSTIPS ARC 28926 15/03/88 info on DOS John Chapman
DOSTIPS1 ARC 159657 25/11/85 various DOS info Dean R. Wood
DOSTIPS3 ARC 59264 25/01/88 various DOS tips (different) Dean R. Wood
DOSUNDOC ARC 3840 03/05/86 one of the very first interrupt lists
Spyros Sakellariadis
DRIVPARM ARC 11264 7/01/88 info on DRIVPARM parameters Joan Friendman
EGATEK ARC 8704 15/03/88 IBM EGA registers Bill Frantz
EMS40BIX ARC 3802 21/09/87 BIX announcement of EMS 4.0 BIX
ENVIRONM ARC 4255 18/09/88 info on DOS environment Jan Fagerholm
ESC_CODE ARC 3072 3/10/88 Laserjet setup codes S. Noh
FILEIO ARC 8192 24/07/88 TSRs and INDOS flag
FLOPPIES ARC 9216 2/11/87 info on floppy media Ted Jensen
FOSSIL ARC 9031 15/07/87 list of FOSSIL functions Vincent Periello
FXN4BH ASM 4503 1/01/80 odd 4Bh behavior Ray Duncan
HAYESET2 ARC 6479 4/09/86 modem commands Ruth Lubow, Fowler Brown
HD-DATA ARC 4096 19/07/87 list of hard drives & specs
I've seen many similar files. I believe the
original may have been a file or bulletin on
Sparta BBS
HDINFO ARC 11264 19/11/87 updated version of above, evidently by someone
else
HDNOISE ARC 4159 11/11/87 hard disk information Clancy Malloy
HDTIPS ARC 9660 11/10/87 hard disk information Barry Gordon
IBMTAB ARC 7882 15/03/88 general IBM PC tech info John S. Lou
IBMTECH ARC 136064 4/11/88 error codes, other info IBM Corp.
INT-MDOS ARC 20682 31/07/85 one of the original INT lists Ross Greenberg
INTER189 LZH 156368 25/06/89 interrupt list Ralf Brown
INTERRUP ARC 157440 19/09/88 interrupt vector list Ralf Brown
INTERRPT ARC 42632 4/04/88 interrupt vector list Marshall Presnell
this is a very nice list and some programming
information. If I'd come across it way back
then it would have saved a ton of typing
JARGON ARC 49274 16/07/88 dictionary of computer terms
LE_MCLCK.ASM 3489 3/27/86 undoc'd Leading Edge BIOS fns Bob Plouffe
LIM-40 ARC 21504 15/10/87 info on LIM 4.0 Stephen Satchell
LISTINTS ARC 6144 3/12/87 small interrupt list
MCB ARC 5120 24/07/88 info on DOS Memory Control Blocks David Gwillim
MNP-TEXT ARC 6144 30/09/88 MNP modem info Mike Focke
MOUSENG ARC 10240 13/08/88 Norton Guide file for mouse programming, with
C examples
MSLOOKUP ARC 58368 25/12/87 interrupt and function listing Frank Bonita
MS-OS2 ARC 25600 15/10/87 MS press release on OS/2 Microsoft Corp.
MSINT125 ARC 48128 12/01/88 interrupt vector listing Ralf Brown
NETBIOS ARC 17280 29/10/88 NetBIOS tutorial & summary Tom Thompson
NOVELINT ARC 4531 18/10/88 NetBIOS calls Marc Guyot
OCOM_520 ARC 53632 19/08/88 FOSSIL tutorial and functions Rick Moore
ODDITY ARC 3072 24/07/88 int 2Eh description Daniel Briggs
PINS ARC 3072 18/01/88 pinouts of various connectors
QUES40 ARC 9081 1/09/88 info on DOS 4.0 IBM Corp.
RAW_COOK ARC 2048 15/10/87 info on DOS raw and cooked modes
RESETSWT TXT 3584 23/01/86 add a reset switch to a PC Don Jenkins
RLLHINTS ARC 12288 17/10/87 RLL controller info Steve Sneed
RLLMISC ARC 5120 17/10/87 info on RLL controllers Richard Driggers
RLLSTORY ARC 9718 31/07/88 good info on RLL coding Pete Holzmann
SEAGATE ARC 2048 3/03/88 specs for many Seagate drives Jim McKown
SECRETS2 ARC 179625 17/04/88 BIX "MS-DOS Secrets" #2
SERCBL2 ARC 4372 16/10/88 serial cable pinouts Lee Zeis
SM2400 ARC 2296 9/08/86 Hayes 2400 baud command set
SPOOL DOC 29704 03/28/89 Versa-Spool API Jeff Newbro
SSTEP ARC 2300 11/07/89 explanation of CPU single-step Ed Burnette
ST225 ARC 11264 7/10/87 optimizing ST225 and WD cont. Neil Erbe
TANDON ARC 3612 21/02/88 info on Tandon drives David Welcher
TECH ARC 27827 8/05/88 misc tech info - Fidonet?
TOOLS C 14032 8/10/89 Grid laptop special functions Fredrick Coffman
TOS 938 24/03/88 TOS function calls Mike Crawford
TRYST ARC 29312 29/10/88 DOS and hard disk info Amy Goebel
UNDOCINT 21H 7168 14/04/87 undocumented DOS calls Peter Holzmann
VESA TXT 41269 01/17/90 VESA standard VESA
VGAKIT DOC 7634 05/04/90 VGA programming kit John Bridges
VGAPIN ARC 1252 24/10/88 VGA pinout "Mike"
WD-27X ARC 6144 10/10/87 WD 27X HD controller setup Steve Shelton
WDCONFIG ARC 5504 11/10/87 WD-1002 WXS setup Richard Driggers
WDCONT ARC 11264 25/12/87 info on WD hard disk controllers Peter Fales
XEB1210 ARC 7947 18/07/87 Xebec HD controller setup Richard Driggers
XEBEC ARC 1036 30/04/88 setup for Xebec HD controller Richard Driggers
XEBECTEC ARC 1834 30/04/88 setup for Xebec 1210
XGADEMO LZH 23552 01/27/91 IBM XGA programming info v.50 Bert Tyler
XMS ARC 75776 1/08/88 Microsoft Extended Memory Specification 1.0
Microsoft Corporation
XTCHARTS ARC 12416 4/11/88 ports, charts
**********************************
NBRCV.C Paul McGinnis NetBIOS API calls
DESQ10.ASM James H. LeMay DesqView API calls
NETTUT.DOC Charles L. Hedrick TCP/IP network
CED10D Chris Dunford CED interrupt calls
LANTSTIC.DOC LANtastic adware peer-to-peer LAN calls
GLOSSARY.ARC no author name computer terms
4DOS.DOC Tom Rawson 4DOS int 2Eh, 2Fh calls, SHELL= bug
DOSREF isn't a tutorial, and sometimes you need a tutorial. Microsoft has
finally written a half-decent one - The MS-DOS Programmer's Reference,
Microsoft Press, 1991, ISBN 1-55615-329-5. This is the DOS 5.0 Tech Ref.
It covers data structures and DOS programming concepts clearly. However,
it has no information on other DOS versions, nor does it (of course) cover
undocumented calls.
------------------------------------
Nothing gets written in a vacuum, and I'd like to express my thanks to all
the people who have been good enough to furnish information and support:
(in alphabetical order)
Tommy Apple, Mike Crawford, Herman Diagostino, Joe Felix, Ron Melson,
Denis Murphy, & Ben Sansing,
who all loaned me documentation and reference material for so long
that some of them have forgotten to ask for their stuff back
And those users who were kind enough to help out:
Mike Blaszczak, MA: (blaszczak on BIX)
who went rampaging through work and client's sites to find and
document various model ID bytes, plus plenty of information on MS OBJ
file formats
Carl Bretteville, Drammen Norway:
who sent me a complete Concurrent DOS Programmer's Reference,
considerably enriching the Norwegian postal service thereby
Herman Diagostino, Manassas VA:
who worked up the TECHMENU menu file and provided a copy of the
rare IBM DOS 4.0 Technical Reference and a copy of the original MSDOS
Encyclopedia from Microsoft, info on the Pelican 5.5mb floppy drive,
IBM DOS 4.0 command reference, many hard drive specs
James Drenter, Davenport IA:
additional info on int 1Ch
David Dorling, Buderim, Australia:
found one embarrassing error in the device driver info and provided
many expansions and clarifications
Chris Dunford, Columbia MD: (CIS 76703,2002)
who sent me a copy of the PCED 2.0 API
Steve Grant, Jersey City NJ: (sjgrant on BIX)
who granted permission to include his excellent SYSID program with my
distribution disks, furnished several model IDs
Roedy Green, Vancouver BC Canada: (roedy on BIX)
many names and addresses for Appendix 5, serial and parallel port
details and cabling, granted permission to include some of his very
educational essays with my distribution disks, plus many details on
DOS disk I/O
Michael Koepke, Wood Dale IL:
pinouts on EGA feature connector, PS/2 keyboard connector, DR-DOS
programming information, much info on Digital's DR-DOS
Curt Lankford, Little Rock, AR:
loaned his copy of the AT&T 6300 Plus Hardware Technical Reference
Alan R. Levinstone, Garland TX:
80286 LOADALL instruction
BIOS Data Area floppy control parameters 40:8B, 40:8F, 40:90
Brian Long, Twyford UK:
provided a copy of the then-nearly-unavailable DPMI 0.9 specification,
plus port and address info
Keith Meade, Rochester MN: (keithm on BIX)
who provided a Microsoft Windows 2.11 SDK, copy of IBM TopView
Feico Nater, Hengelo, Netherlands:
additions to FCB calls, several pages of expansions and clarifications
Bruce Nevins, Tucson AZ: (bnevins on BIX)
Irwin low-level tape drive info, DEC PC info
Patrick O'Riva, San Jose CA:
info on what happens to the interleave when the BIOS is finished, and
for his interesting online assembly-language magazine
Klaus Overhage, Stuttgart W.Germany:
FANSI-CONSOLE system calls, and translating the TechRef into German
John Richards, England: (jrichards on BIX)
European DOS 4.0 information
Ben Sansing, Little Rock AR:
ANSI.SYS information, documentation for the NEC V20/30 chips, reported
error in register chart in Chapter 4, loaned his copy of PC-MOS/386
for testing
Hans Schleichert, Marburg West Germany:
information on int 2Fh, fn OAEh (internal DOS commands). Good thing
I took some German in high school...
John Switzer, CA: (jswitzer on BIX)
who allowed me to include his discoveries on alternate DOS entries
and file mysteries. (see BACKDOOR.ZIP on BIX, or Oct 1990 Dr. Dobbs')
Fred Thompson, Rapid City SD:
loaned his Sound Blaster manual, provided much info on graphics
programming
Matt Trask: (matt.trask on BIX)
who donated a complete copy of the TopView Programmer's Reference
Richard Vogh, Marietta GA:
found several embarrassing errors in the boot sector chart in Chapter
8. The shame! The shame!
Jim Wenzel, North Little Rock AR:
more PC model ID codes, loaned his copy of the Windows 3.0 SDK
The Software Link, Atlanta GA:
provided a review copy of PC/MOS-386 and the programming guide
Digital Research, Monterrey CA:
provided review copies of DR-DOS 5.0 and DRMDOS
Microsoft Corporation, Redmond WA:
for beta-test versions of DOS 5.0, Windows 3.1, other products,
information on DOS 5 and the DOSSHELL API
Special thanks to Chris Dunford, who donated his "CED" program to the public
domain. If it wasn't for CED, I would likely have abandoned MSDOS machines
entirely and bought a Macin...uh... something else; and to Haruyasu Yoshizaki
for allowing unrestricted use of his LHarc program used to compress the files
on these diskettes.
Dave Williams
--------------------
Jacksonville, AR
** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴캑 DOSREF (tm) 쳐컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
� Shareware Version, 01/12/92 �
� Please Register Your Copy �
읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴�
Additional Readings...
I don't have and haven't seen most of this stuff, but I've come across
mentions of it. This list is purely FYI...
IBM's literature guide lists the following manuals:
Hardware Technical References:
PS/2 Model 25 $31.50 75X1055
PS/2 Model 30 $82.50 68X2201
PS/2 Model 30/286 $26.75 01F0237
PC $33.00 6322507 (the original)
PC/AT $115.00 6280070
supplement for AT/339 $54.50 6280099 (enhanced 8mHz)
XT/286 $55.00 68X2210
XT and Portable $54.50 6280089
Convertible $82.50 6280648
PCjr $38.50 1502293 (availability varies)
PS/2 Hardware Interface $137.00 68X2330
(Micro Channel docs)
PS/2 BIOS Interface $137.00 68X2341 (no source code listing)
Advanced BIOS Interface $50 68X2288
DOS 3.3 Technical Ref. $93.00 6280059 (no reference for 4.0)
DOS 4.0 Command Ref. $31.50 6280253 (commands only)
8514/A Developer's Guide $26.75 68X2279
There is supposed to be a DOS 4.0 Technical Reference, but there's no name or
part number listed in the official IBM literature. You might check with your
local IBM retailer. (hah!)
DOS 4.0 Technical Ref. $--.-- 6280254 (not listed in catalog)
IBM NetBIOS Application
Development Guide (API) $49.25 68X2270 (not listed in catalog)
address:
IBM Technical Directory 800-426-7282
PO Box 2009 414-633-8108
Racine WI 53404-3336 BC, Canada 112-800-465-1234
Canada 800-465-1234
catalogs are free
Zenith Data Systems' "MS-DOS version 2 Programmer's Utility" comes with MASM,
a version of the MS-DOS Programmer's Reference from Microsoft, the assembly
language source for Zenith's ANSI.SYS driver, an editor, an assortment of
filters and utilities, and the source listing for the "device dependent"
portion of MS-DOS for the Z-151.
"Document Content Architecture: Revisable - Form - Text Reference"
IBM Document SC23-0758-1
IGES (International Graphics Exchange Specification) 3.0 documentation,
Global Engineering Documents (800) 854-7179. Part number NBSIR 86-3359, NBS.
ISBN 0-672-22027-X "Interfacing To the IBM Personal Computer" by
Lewis C. Eggebrecht, Howard W Sams & Co., Indianapolis, IN.
Intel Application Note AP-133, "Getting Started with the Numeric Data
Processor," by Bill Rash. February 1981.
Intel iAPX 286 Programmer's Reference Manual, including the iAPX 286
Numeric Supplement, Intel part no. 210498-003. Has some reasonably useful
example codes in section 4, including ASCII to binary and vice versa on
pages 4-7 to 4-14 and trig functions on 4-18 to 4-23. The programming
style in these examples is rather bizarre but they are better than nothing.
Intel 80387 Programmer's Reference Manual, Intel part no. 231917-001.
Various example listings on pages 7-7 to 7-17, including ASCII to binary
and binary to ASCII conversions and raising a number to a power. No trig
routines in this manual because the 80387 has built-in FSIN, FCOS, and FSINCOS
instructions and generalized FPTAN and FPATAN instructions that make
subroutines unnecessary.
Hercules sells a graphics library for the Herc board called GRAPHX for $50.
DoD Trusted Computer System Evaluation Criteria (popularly known as "The
Orange Book) GPO Stock No 008-000-00461-7 Cost $6.00
Information Interchange Standards:
ANSI X 3.15-1976 (FIPS 16-1)
Bit Sequencing In Serial-By-Bit Data Transmission.
ANSI X3.16-1976 (FIPS 17-1)
Character Structure and Parity-Sense, Serial-By-Bit.
ANSI X3.25-1976 (FIPS 18-1)
Character Structure and Parity-Sense, Parallel-By-Bit.
ANSI X3.4-1977 (FIPS 1-1)
Code for Information Interchange
ANSI X3.41-1974 (FIPS 35)
Code Extension Techniques for Use With 7-Bit Coded Characters.
ANSI X3.64-1979 (FIPS 86)
Additional Controls for Use With...
ANSI X3.32-1973 (FIPS 1)
Graphic Representation of the Control Characters.
ANSI X3.78-1981
Representation of Vertical Carriage positoning Characters.
ANSI X3.42-1975
Representation of numeric values in Character Strings.
ANSI X3.98-1983
Page Image Format (PIF), Text, for Information Systems.
ANSI X3.28-1976
Procedure for the Use of Communications Control Characters.
ANSI X3.66-1979 (FIPS 71)
Advanced Data Communications Control Procedures (ADCCP)
Data Encryption Standards:
ANSI-X3.92-1981
Data Encryption Algorithm
ANSI-X3.105-1983
Data Link Encryption
ANSI-X3.106-1983
Modes of Operation of Data Encryption Algorithm
Serial Interface Standards:
RS-232-C Aug 1969 (June 1981)
Interface Between Data Terminal Equipment (DTE) and
Data Communications Equipment (DCE)
Bulletin #9 May 1971 (Application Notes)
...reviews methods of operation...service and trans-
mission facility characteristics...
Bulletin #12 Nov 1977 (Application Notes)
Interconnection Between RS-449 and RS-232-C ...
Bulletin #14 Mar 1982 (Application Notes)
Loop Test Circuits Not Defined in RS-232-C
RS-336-A Mar 1979
Interface Between DTE and Automatic Calling Equipment
RS-449 Nov 1977
RS-449-1 Addendum 1 Feb 1980
General Purpose 37- and 9-Position Interface for DTE
and Data Circuit-Terminating Equipment (DCE)...
Standards Groups:
AFIP (Federal Information Processing Standards)
Office of Technical Information and Publications
National Bureau of Standards
Washington, D.C. 20234
ANSI American National Standards Institute, Inc.
1430 Broadway
New York, New York 10018
BELL ??
EIA Electronic Industries Association
2001 Eye Street
Washington, D.C. 20006
CCITT ??
ISO International Standards Organization
(available through ANSI)
Coding and Information Theory by Richard W. Hamming (Prentice-Hall, 1980)
Error Correcting Codes by W. Wesley Peterson (MIT Press and Wiley, 1961)
Handbook of Software & Hardware Interfacing for IBM PCs
Jefferey P. Royer
1987 by Prentice-Hall, Inc. (Osborne-McGraw-Hill)
Englewood Cliffs, NJ 07632
ISBN 0-13-381831-4 hardware and expansion card design and interfacing
The C Programmer's Guide to NetBios, W. David Schwaderer, Howard W Sams &
Company, ISBN 0-672-22638-3 $24.95.
Computer Networks - Andrew S. Tanenbaum,Prentice Hall, ISBN 0-13-162959-X
Local Area Networks - Thomas W.Madron - Wiley, ISBN 0-471-85989-3
Netware APIs: There are many API packages available from Novell. Some of them:
Value-Added Process API $10.00 part number 420-10361-001
Netware Enhancements Package (security APIs, Queue Management, Accounting
Services) $15.00 part number 420-010316-110
Peer to Peer Comm. $15.00 part # 421-10070-001
Message Handling Service Interface $15.00 part # 420-10360-001
Novell API Reference Manual vols 1 & 2 $25.00 each part #s 452-760041-001
and 452-760042-001
C language Novell API Reference $250.00 part # 452-760043-001
Programmer's Guide $49.00 part # 420-000089-001
NetWare Technical Journal, 650 South Clark, Chicago, IL 60605-9960, pub. four
times a year for $50.00/yr.
SCSI specification: $25 from the American National Standards Institute,
1430 Broadway, New York, NY 10018, (212) 642-4900.
SCSI-2 X3T9.2 committee working documents, CAM committee documents, and the
most current draft of the SCSI-2 specification are available for downloading
from the SCSI BBS at (316) 636-8700 (300, 1200, or 2400 bps; 24 hours).
A paper copy of the SCSI-2 draft specification is available for $60 from
Global Engineering Documents 2805 McGaw Ave., Irvine, CA 92714,
(800) 854-7179 or (714) 261-1455.
SMB protocol (used by Microsoft in MS-Net and Lan Manager) "IBM Personal
Computer Seminar Proceedings", Volume 2, Number 8-1, G320-9310-00.
Security (DES, etc): NCSC's VENDOR'S GUIDE (dark green book [part of the
Rainbow series of books]). Write to: National Security Agency, ATTN: S613,
Ft. George Meade, MD 20755-6000, or call (301) 688-6581.
Programmer's Guide to PC & PS/2 Video Systems
Richard Wilton
Microsoft Press 1987
ISBN 1-55615-103-9
Logitech Mouse Tech. Ref. and Programmer's Guide v2.0, $25 (415)795-0801
============================== I N V O I C E =================SWv2.2a=======
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