Programmer's Technical Reference for MSDOS and the IBM PC

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** Programmer's Technical Reference for MSDOS and the IBM PC **
USA copyright TXG 392-616 ALL RIGHTS RESERVED
ДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ DOSREF (tm) ГДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД
ISBN 1-878830-02-3 (disk-based text)
Copyright (c) 1987, 1992 Dave Williams
ЪДДДДДДДДДДДДДДДДДДДДДДДДДДДДДї
і Shareware Version, 01/12/92 і
і Please Register Your Copy і
АДДДДДДДДДДДДДДДДДДДДДДДДДДДДДЩ

/* 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

/* 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.

ЙНННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННН»
є Programmer's Technical Reference for MSDOS and the IBM PC SWv2.2a є
ИННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННННј

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:

СНННННННННННННННННННННННННННННС
і Dave Williams, DOSREF і
і PO Box 181 і
і Jacksonville, AR 72076-0181 і
і USA і
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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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і Spearwood Shareware Service і
і PO Box 121 і
і Hamilton Hill, WA 6163 і
і Australia і
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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 њ16.95 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.

ЪДДДДДДї
іЪДДДДДЩ
іАДДДДДї
ГВДДВДДґ Approved
іі іЪїі Author
іАДДЩііі
ГВДДВББґ User -
іі іЪїі Supported
іАДДЩііі Software
ГДДДВЩГґ Association
іЪДїі іі
іАДЩАДЩі
АДДДДДДЩ
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)

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

C H A P T E R O N E

DOS AND THE IBM PC

C O N T E N T S

SOME HISTORYГДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД 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?ГДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД 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 SYSTEMSГДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД 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-DOSГДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД 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 HIERARCHYГДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД 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 STRUCTUREГДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД 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 INITIALIZATIONГДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД 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.

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

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.

ЪДДДДДДВДДДДДВДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДї
іstart іstartіend і і
іaddr. іaddr.іaddr.і usage і
і(dec) і (hex) і і
ГДДДДДДБДДДДДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і *640k RAM Area* і
ГДДДДДДВДДДДДДДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 0k і і start of RAM, first K is interrupt vector table і
і 16k і00000-03FFFі PC-0 system board RAM ends і
і 32k і04000-07FFFі і
і 48k і08000-0BFFFі і
ГДДДДДДЕДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 64k і10000-13FFFі PC-1 system board RAM ends і
і 80k і14000-17FFFі і
і 96k і18000-1BFFFі і
і 112k і1C000-1FFFFі і
ГДДДДДДЕДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 128k і20000-23FFFі і
і 144k і24000-27FFFі і
і 160k і28000-2BFFFі і
і 176k і2C000-2FFFFі і
ГДДДДДДЕДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 192k і30000-33FFFі і
і 208k і34000-37FFFі і
і 224k і38000-3BFFFі і
і 240k і3C000-3FFFFі і
ГДДДДДДЕДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 256k і40000-43FFFі PC-2 system board RAM ends і
і 272k і44000-47FFFі і
і 288k і48000-4BFFFі і
і 304k і4C000-4FFFFі і
ГДДДДДДЕДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 320k і50000-53FFFі і
і 336k і54000-57FFFі і
і 352k і58000-5BFFFі і
і 368k і5C000-5FFFFі і
ГДДДДДДЕДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 384k і60000-63FFFі і
і 400k і64000-67FFFі і
і 416k і68000-6BFFFі і
і 432k і6C000-6FFFFі і
ГДДДДДДЕДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 448k і70000-73FFFі і
і 464k і74000-77FFFі і
і 480k і78000-7BFFFі і
і 496k і7C000-7FFFFі і
ГДДДДДДЕДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 512k і80000-83FFFі і
і 528k і84000-87FFFі і
і 544k і88000-8BFFFі the original IBM PC-1 BIOS limited memory to 544k і
і 560k і8C000-8FFFFі і
ГДДДДДДЕДДДДДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 576k і90000-93FFFі і
і 592k і94000-97FFFі і
і 609k і98000-9BFFFі і
і 624k і9C000-9FFFFі to 640k (top of RAM address space) і
ГДДДДДДБДДДДДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
іA0000 ***** 64k ***** EGA/VGA starting address і
іA0000 ***** 64k ***** Toshiba 1000 DOS ROM (MS-DOS 2.11V) і
ГДДДДДДВДДДДДДДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 640k іA0000-A95B0і MCGA 320x200 256 color video buffer і
і і -AF8C0і MCGA 640x480 2 color video buffer і
і і -A3FFFі і
і 656k іA4000-A7FFFі і
і 672k іA8000-ABFFFі this 64k segment may be used for contiguous DOS і
і 688k іAC000-AFFFFі RAM with appropriate hardware and software і
ГДДДДДДБДДДДДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
іB0000 ***** 64k ***** mono and CGA address і
ГДДДДДДВДДДДДДДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 704k іB0000-B3FFFі 4k monochrome display | The PCjr and early Tandy 1000і
і 720k іB4000-B7FFFі | BIOS revector direct write toі
і 736k іB8000-BBFFFі 16k CGA uses | the B8 area to the Video Gateі
і 756k іBC000-BFFFFі | Array and reserved system RAMі
ГДДДДДДБДДДДДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
іC0000 ***** 64k *************** expansion ROM і
ГДДДДДДВДДДДДДДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 768k іC0000-C3FFFі 16k EGA BIOS C000:001E EGA BIOS signature (letters IBM і
і 784k іC4000-C5FFFі і
і іC6000-C63FFі 256 bytes Professional Graphics Display comm. area і
і іC6400-C7FFFі і
і 800k іC8000-CBFFFі 16k hard disk controller BIOS, drive 0 default і
і іCA000 і some 2nd floppy (high density) controller BIOS і
і 816k іCC000-CDFFFі 8k IBM PC Network NETBIOS і
і іCE000-CFFFFі і
ГДДДДДДБДДДДДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
іD0000 ***** 64k ***** expansion ROM і
ГДДДДДДВДДДДДДДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 832k іD0000-D7FFFі 32k IBM Cluster Adapter | PCjr first ROM cartridge і
і і DA000і voice communications | address area. і
і 848k іD4000-D7FFFі | Common expanded memory board і
і 864k іD8000-DBFFFі | paging area. і
і 880k іDC000-DFFFFі | і
і іDE000 і TI Pro default video buffer, 4k in length і
ГДДДДДДБДДДДДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
іE0000 ***** 64k ***** expansion ROM і
ГДДДДДДВДДДДДДДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 896k іE0000-E3FFFі | PCjr second ROM cartridge і
і 912k іE4000-E7FFFі | address area і
і 928k іE8000-EBFFFі | і
і 944k іEC000-EFFFFі | spare ROM sockets on AT і
ГДДДДДДБДДДДДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
іF0000 ***** 64k ***** system і
ГДДДДДДВДДДДДДДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 960k іF0000-F3FFFі reserved by IBM | cartridge address і
і 976k іF4000- і | area (PCjr cartridge і
і іF6000 і ROM BASIC Begins | BASIC) і
і 992k іF8000-FB000і | і
і 1008kіFC000-FFFFFі ROM BASIC and original | і
і і і BIOS (Compatibility BIOS | і
і і і in PS/2) | і
і 1024kі FFFFFі end of memory (1024k) for 8088 machines і
ГДДДДДДЕДДДДДДДДДДДБДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 384k і100000-15FFFFі 80286/AT extended memory area, 1Mb motherboard і
і 15Mb і100000-FFFFFFі 80286/AT extended memory address space і
і 15Mb і160000-FDFFFFі Micro Channel RAM expansion (15Mb extended memory) і
і 128k іFE0000-FFFFFFі system board ROM (PS/2 Advanced BIOS) і
ГДДДДДДЕДДДДДДДДДДДДДБДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і 64k іC0000000-C000FFFFі Weitek "Abacus" math coprocessor memory-mapped I/O і
АДДДДДДБДДДДДДДДДДДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДЩ

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

ЪДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД
і 000-3FF - 1k DOS interrupt vector table, 4 byte vectors for ints 00h-0FFh.
і 30:00 - used as a stack area during POST and bootstrap routines. This
іto 3F:FF stack area may be revectored by an application program.
ГДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД
і ** The BIOS Data Area ** addresses from 400h to 4FFh
ГДДДДДВДДДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД
іaddr.і size і description
ГДДДДДЕДДДДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД
і40:00і word і COM1 port address | These addresses are zeroed out in the
і40:02і word і COM2 port address | OS/2 DOS Compatibility Box if any of
і40:04і word і COM3 port address | the OS/2 COMxx.SYS drivers are loaded.
і40:06і word і COM4 port address |
і40:08і word і LPT1 port address
і40:0Aі word і LPT2 port address
і40:0Cі word і LPT3 port address
і40:0Eі word і LPT4 port address (not valid in PS/2 machines)
і40:0Eі word і PS/2 pointer to 1k extended BIOS Data Area at top of RAM
і40:10і word і equipment flag (see int 11h)
АДДДДДБДДДДДДДґ bits:
і 0 0 no floppy drive present
і 1 if floppy drive present (see bits 6&7)
і 1 0 no math coprocessor installed
і 1 if 80x87 installed (not valid in PCjr)
і 2,3 system board RAM (not used on AT or PS/2)
і 0,0 16k 0,1 32k
і 1,0 48k 1,1 64k
і 4,5 initial video mode
і 0,0 no video adapter
і 0,1 40 column color (PCjr default)
і 1,0 80 column color
і 1,1 MDA
і 6,7 number of diskette drives
і 0,0 1 drive 0,1 2 drives
і 1,0 3 drives 1,1 4 drives
і 8 0 DMA present
і 1 DMA not present (PCjr, Tandy 1400, Sanyo 55x)
і 9,A,B number of RS232 serial ports
і C game adapter (joystick)
і 0 no game adapter
і 1 if game adapter
і D serial printer (PCjr only)
і 0 no printer
і 1 serial printer present
ЪДДДДДДЩ E,F number of parallel printers installed
іnote 1) The IBM PC and AT store the settings of the system board
АДДДї switches or CMOS RAM setup information (as obtained by the BIOS
і in the Power-On Self Test (POST)) at addresses 40:10h and
і 40:13h. 00000001b indicates "on", 00000000b is "off".
ЪДДДДДВДДДДБДДї
і40:12і byte і reserved (PC, AT)
АДДДДДБДДДДДДДґ number of errors detected by infrared keyboard link (PCjr)
ЪДДДДДВДДДДДДДґ POST status (Convertible)
і40:13і word і availible memory size in Kbytes (less display RAM in PCjr)
ГДДДДДЕДДДДДДДґ this is the value returned by int 12h
і40:15і word і reserved
і40:17і byte і keyboard flag byte 0 (see int 9h)
АДДДДДБДДДДДДДґ bit 7 insert mode on 3 alt pressed
і 6 capslock on 2 ctrl pressed
і 5 numlock on 1 left shift pressed
ЪДДДДДВДДДДДДДґ 4 scrollock on 0 right shift pressed
і40:18і byte і keyboard flag byte 1 (see int 9h)
АДДДДДБДДДДДДДґ bit 7 insert pressed 3 ctrl-numlock (pause) toggled
і 6 capslock pressed 2 PCjr keyboard click active
і 5 numlock pressed 1 PCjr ctrl-alt-capslock held
ЪДДДДДВДДДДДДДґ 4 scrollock pressed 0
і40:19і byte і storage for alternate keypad entry (not normally used)
і40:1Aі word і pointer to keyboard buffer head character
і40:1Cі word і pointer to keyboard buffer tail character
і40:1Eі32bytesі 16 2-byte entries for keyboard circular buffer, read by int 16h
і40:3Eі byte і drive seek status - if bit=0, next seek will recalibrate by
АДДДДДБДДДДДДДґ repositioning to Track 0.
і bit 3 drive D bit 2 drive C
ЪДДДДДВДДДДДДДґ 1 drive B 0 drive A
і40:3Fі byte і diskette motor status (bit set to indicate condition)
АДДДДДБДДДДДДДґ bit 7 write in progress 3 motor on (floppy 3)
і 6 2 motor on (floppy 2)
і 5 1 B: motor on (floppy 1)
ЪДДДДДВДДДДДДДґ 4 0 A: motor on (floppy 0)
і40:40і byte і motor off counter
і і і starts at 37 and is decremented 1 by each system clock tick.
і і і motor is shut off when count = 0.
і40:41і byte і status of last diskette operation where:
АДДДДДБДДДДДДДґ bit 7 timeout failure 3 DMA overrun
і 6 seek failure 2 sector not found
і 5 controller failure 1 address not found
ЪДДДДДВДДДДДДДґ 4 CRC failure 0 bad command
і40:42і7 bytesі NEC floppy controller chip status
і40:49і byte і Video Control Data Area 1 from 0040:0049 through 0040:0066
АДДДДДБДДДДДДДґ current CRT mode (hex value)
і 00h 40x25 BW (CGA) 01h 40x25 color (CGA)
і 02h 80x25 BW (CGA) 03h 80x25 color (CGA)
і 04h 320x200 color (CGA) 05h 320x200 BW (CGA)
і 06h 640x200 BW (CGA) 07h monochrome (MDA)
іextended video modes (EGA/MCGA/VGA or other)
і 08h lores,16 color 09h med res,16 color
і 0Ah hires,4 color 0Bh n/a
і 0Ch med res,16 color 0Dh hires,16 color
ЪДДДДДВДДДДДДДґ 0Eh hires,4 color 0Fh hires,64 color
і40:4Aі word і number of columns on screen, coded as hex number of columns
АДДДДДБДДДДДДДґ 20 col = 14h (video mode 8, low res 160x200 CGA graphics)
і 40 col = 28h
ЪДДДДДВДДДДДДДґ 80 col = 46h
і40:4Cі word і screen buffer length in bytes
ГДДДДДЕДДДДДДДґ(number of bytes used per screen page, varies with video mode)
і40:4Eі word і current screen buffer starting offset (active page)
і40:50і8 wordsі cursor position pages 1-8
АДДДДДБДДДДДДДґ the first byte of each word gives the column (0-19, 39, or 79)
ЪДДДДДВДДДДДДДґ the second byte gives the row (0-24)
і40:60і byte і end line for cursor (normally 1)
і40:61і byte і start line for cursor (normally 0)
і40:62і byte і current video page being displayed (0-7)
і40:63і word і base port address of 6845 CRT controller or equivalent
ГДДДДДЕДДДДДДДґ for active display 3B4h=mono, 3D4h=color
і40:65і byte і current setting of the CRT mode register
і40:66і byte і current palette mask setting (CGA)
і40:67і5 bytesі temporary storage for SS:SP during shutdown (cassette interface)
і40:6Cі word і timer counter low word
і40:6Eі word і timer counter high word
і40:69і byte і HD_INSTALL (Columbia PCs) (not valid on most clone computers)
АДДДДДБДДДДДДДґ bit 0 0 8 inch external floppy drives
і 1 5-1/4 external floppy drives
і 1,2 highest drive address which int 13 will accept
і (since the floppy drives are assigned 0-3,subtract
і 3 to obtain the number of hard disks installed)
і 4,5 # of hard disks connected to expansion controller
і 6,7 # of hard disks on motherboard controller
і (if bit 6 or 7 = 1, no A: floppy is present and
ЪДДДДДВДДДДДДДґ the maximum number of floppies from int 11 is 3)
і40:70і byte і 24 hour timer overflow 1 if timer went past midnight
ГДДДДДЕДДДДДДДґ it is reset to 0 each time it is read by int 1Ah
і40:71і byte і BIOS break flag (bit 7 = 1 means break key hit)
і40:72і word і reset flag
АДДДДДБДДДДДДДґ PCjr keeps 1234h here for softboot when a cartridge is installed
і bits 1234h = soft reset, memory check will be bypassed
і 4321h = preserve memory (PS/2 only)
і 5678h = system suspended (Convertible)
і 9ABCh = manufacturing test mode (Convertible)
ЪДДДДДВДДДДДДДґ ABCDh = system POST loop mode (Convertible)
і40:74і byte і status of last hard disk operation ; PCjr special disk control
і40:75і byte і # of hard disks attached (0-2) ; PCjr special disk control
і40:76і byte і HD control byte; temp holding area for 6th param table entry
і40:77і byte і port offset to current hd adapter ; PCjr special disk control
і40:78і4 bytesі timeout value for LPT1,LPT2,LPT3,LPT4
і40:7Cі4 bytesі timeout value for COM1,COM2,COM3,COM4 (0-0FFh secs, default 1)
і40:80і word і pointer to start of circular keyboard buffer, default 03:1E
і40:82і word і pointer to end of circular keyboard buffer, default 03:3E
АДДДДДБДДДДДДДґ note: early Zenith Z183 BIOS set these pointers to zero and
ЪДДДДДВДДДДДДДґ ignored them.
і40:84і .... і Video Control Data Area 2, 0040:0084 through 0040:008A
і40:84і byte і rows on the screen minus 1 (EGA only)
і40:84і byte і PCjr interrupt flag; timer channel 0 (used by POST)
і40:85і word і bytes per character (EGA only)
і40:85і2 bytesі (PCjr only) typamatic character to repeat
і40:86і2 bytesі (PCjr only) typamatic initial delay
і40:87і byte і mode options (EGA only)
АДДДДДБДДДДДДДґ bit 0 0 cursor emulation in effect
і 1 no cursor emulation
і 1 0 EGA is connected to a color display
і 1 EGA is connected to monochrome TTL display
і 2 0 wait for vertical retrace (CGA active)
і 1 don't wait for vertical retrace (EGA or MDA active)
і 3 0 EGA is the active display,
і 1 "other" display is active.
і 4 reserved
і 5,6 EGA memory size
і 0,0 64k
і 0,1 128k
і 1,0 192k
і 1,1 256k
і 7 0 don't clear screen on mode changes
і 1 if the last "set mode" specified not to clear the
і video buffer
і mode combinations:
і bit3 bit1 Meaning
і 0 0 EGA is active display and is color
і 0 1 EGA is active display and is monochrome
і 1 0 EGA is not active, a mono card is active
ЪДДДДДВДДДДДДДґ 1 1 EGA is not active, a CGA is active
і40:87і byte і (PCjr only) current Fn key code
ГДДДДДЕДДДДДДДґ 80h bit indicates make/break key code?
і40:88і byte і feature bits and switches (EGA only) 0=on, 1=off
АДДДДДБДДДДДДДґ bit 0 switch 1
і 1 switch 2
і 2 switch 3
і 3 switch 4
ЪДДДДДВДДДДДДДґ 4-7 feature bits
і40:88і byte і (PCjr only) special keyboard status byte
АДДДДДБДДДДДДДґ bit 7 function flag 3 typamatic (0=enable,1=disable)
і 6 Fn-B break 2 typamatic speed (0=slow,1=fast)
і 5 Fn pressed 1 extra delay bef.typamatic (0=enable)
ЪДДДДДВДДДДДДДґ 4 Fn lock 0 write char, typamatic delay elapsed
і40:89і byte і (PCjr) current value of 6845 reg 2 (horizontal synch) used by
АДДДДДБДДДДДДДґ ctrl-alt-cursor screen positioning routine in ROM
і (VGA)
і bit 0 reserved
і 1 video summing enabled
і 2 0 for color monitor attached
і 1 for mono monitor
і 3 0 for default palette loading enabled
і 4 0 for 8x8 text font
і 1 for 8x16 text font
ЪДДДДДВДДДДДДДґ 5-7 reserved
і40:8Aі byte і (PCjr) CRT/CPU Page Register Image, default 3Fh
АДДДДДБДДДДДДДґ (VGA) Display Combination Code Index. This is the value
і set/returned by function 1Ah of the Video BIOS. This byte
і contains an index into the ROM BIOS Display Combination Code
і table, which is a list of byte pairs that specify valid
і combinations of one or two video subsystems. Video subsystems
і are designated by the following values:
і 00h no display
і 01h MDA with monochrome display
і 02h CGA with color display
і 03h reserved
і 04h EGA with color display
і 05h EGA with monochrome display
і 06h Professional Graphics Adapter
і 07h VGA with analog monochrome display
і 08h VGA with analog color display
і 09h reserved
і 0Ah MCGA with digital color display
і 0Bh MCGA with analog monochrome display
і 0Ch MCGA with analog color display
ЪДДДДДВДДДДДДДґ 0FFh unrecognized video subsystem
і40:8Bі byte і last diskette data rate selected
АДДДДДБДДДДДДДґ bit 7,6 starting data transfer rate to use
і 0,0 500 kb/sec
і 0,1 300 kb/sec
і 1,0 250 kb/sec
і 1,1 reserved
і 5,4 last step rate selected
і 3 ending data transfer rate to use
і 2 reserved
і 1 reserved
і 0 1 combination floppy/fixed disk controller detected
і 0 XT floppy only controller (for 360kb drive) detected
і Data Transfer Rates
і Kbits/sec Media Drive Sectors/Track
і 250 360k 360k 9
і 300 360k 1.2M 9
і 500 1.2M 1.2M 15
і 250 720k 720k 9
і 250 720k 1.4M 9
ЪДДДДДВДДДДДДДґ 500 1.4M 1.4M 18
і40:8Cі byte і hard disk status returned by controller
і40:8Dі byte і hard disk error returned by controller
і40:8Eі byte і hard disk interrupt (bit 7=working interrupt)
і40:8Fі byte і combo_card - status of drives 0 and 1
АДДДДДБДДДДДДДґ bit 7 reserved
і 6 drive type determined for drive 1
і 5 drive multiple data rate capability for drive 1
і 0 no multiple data rate
і 1 multiple data rate
і 4 1 then drive 1 has 80 tracks
і 0 then drive 1 has 40 tracks
і 3 reserved
і 2 drive type determined for drive 0
і 1 drive multiple data rate capability for drive 0
і 0 no multiple data rate
і 1 multiple data rate
і 0 1 the drive 0 has 80 tracks
ЪДДДДДВДДДДДДДґ 0 the drive 0 has 40 tracks
і40:90і4 bytesі media state drive 0, 1, 2, 3
АДДДДДБДДДДДДДґ floppy_media_state
і bit 7,6 Data transfer rate
і 00 - 500 K/sec
і 01 - 300 K/sec
і 10 - 250 K/sec
і 11 - reserved
і 5 double stepping required
і 4 media/drive determined
і 3 reserved
і 2-0 present state
і 000 360k in 360k unestablished
і 001 360k in 1.2M unestablished
і 010 1.2M in 1.2M unestablished
і 011 360k in 360k established
і 100 360k in 1.2M established
і 101 1.2M in 1.2M established
і 110 reserved
ЪДДДДДВДДДДДДДґ 111 none of the above
і40:94і2 bytesі track currently seeked to drive 0, 1
і40:96і byte і keyboard flag byte 3 (see int 9h)
і40:97і byte і keyboard flag byte 2 (see int 9h)
і40:98і dword і segment:offset pointer to users wait flag
і40:9Cі dword і users timeout value in microseconds
і40:A0і byte і real time clock wait function in use
АДДДДДБДДДДДДДґ bits 7 wait time elapsed and posted flag
і 6-1 reserved
ЪДДДДДВДДДДДДДґ 0 int 15h, function 86h (WAIT) has occurred
і40:A1і byte і LAN A DMA channel flags
і40:A2і2 bytesі status LAN A 0,1
і40:A4і dword і saved hard disk interrupt vector
і40:A8і dword і SAVE_PTR: EGA pointer to table of 7 parameters in segment:
АДДДДДБДДДДДДДґ offset format. Format of table:
і D_1 dword pointer to 1472 byte table of 64 video parameters
і D_2 dword reserved
і D_3 dword reserved
і D_4 dword reserved
і D_5 dword reserved for future use
і D_6 dword reserved for future use
ЪДДДДДВДДДДДДДґ D_7 dword reserved for future use
і40:B0і2 wordsі international support (Tandy 1000 TX)
і40:B4і byte і keyboard NMI control flags (Convertible)
і40:B4і byte і monochrome monitor hookup detect (Tandy 1000 TX)
і і і 00h not present 0FFh present
і40:B5і dword і keyboard break pending flags (Convertible)
і40:B5і byte і extended equipment detect (5 bits) (Tandy 1000 TX)
АДДДДДБДДДДДДДґ bit 0 = 0 drive A is 5¬
і 1 drive A is 3«
і 1 = 0 drive A is 5¬
і 1 drive A is 3«
і 2 = 0 Tandy 1000 keyboard layout
і 1 IBM keyboard layout
і 3 = 0 CPU slow mode
і 1 CPU fast mode
і 4 = 0 internal color video support enabled
і 1 internal color video support disabled, external
і video enabled (chg from mb'd to expansion card)
і 5 = 0 no external monochrome video installed
ЪДДДДДВДДДДДДДґ 1 external monochrome video installed
і40:B6і byte і extended equipment detect (1 bit) (Tandy 1000 TX)
АДДДДДБДДДДДДДґ bit 0 = 0 drive C is 5¬
ЪДДДДДВДДДДДДДґ 1 drive C is 3«
і40:B9і byte і port 60 single byte queue (Convertible)
і40:BAі byte і scan code of last key (Convertible)
і40:BBі byte і pointer to NMI buffer head (Convertible)
і40:BCі byte і pointer to NMI buffer tail (Convertible)
і40:BDі16bytesі NMI scan code buffer (Convertible)
і40:CEі word і day counter (Convertible and after)
і to і -04:8Fі end of BIOS Data Area
ГДДДДДБДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД
і ** End of BIOS Data Area **
ГДДДДДВДДДДДДДВДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД
і40:90і-40:EF і reserved by IBM
і40:F0і16bytesі Inter-Application Communications Area (for use by applications
і40:FFі і to transfer data or parameters to each other)
АДДДДДБДДДДДДДґ 1) Used by Turbo Power's FMARK (mark memory for TSRs).
і 2) Used by Norton Utilities' TimeMark to store the time.
і 3) Used by BRIEF editor.
ЪДДДДДВДДДДДДДґ
і50:00і byte і DOS print screen status flag
АДДДДДБДДДДДДДґ 00h not active or successful completion
і 01h print screen in progress
ЪДДДДДВДДДДДДДґ 0FFh error during print screen operation
і50:01і і Used by BASIC
і50:02-03 і PCjr POST and diagnostics work area
і50:04і byte і Single drive mode status byte - not used by AT&T DOS 2.11!
АДДДДДБДДДДДДДґ 00 logical drive A was last active
ЪДДДДДДДДДДДДДґ 01 logical drive B was last active
і50:05-0E і PCjr POST and diagnostics work area
і50:0Fі і BASIC: SHELL flag (set to 02h if there is a current SHELL)
і50:10і word і BASIC: segment address storage (set with DEF SEG)
і50:12і4 bytesі BASIC: int 1Ch clock interrupt vector segment:offset storage
і50:16і4 bytesі BASIC: int 23h ctrl-break interrupt segment:offset storage
і50:1Aі4 bytesі BASIC: int 24h disk error int vector segment:offset storage
і50:1B-1F і Used by BASIC for dynamic storage
і50:20-21 і Used by DOS for dynamic storage
і50:22-2C і Used by DOS for diskette parameter table. See int 1Eh for values
АДДДДДБДДДДДДДґ In DOS 1.0 this is located in the ROM BIOS, but in DOS 1.1 and
і subsequent it is a part of DOS located at 05:22. The first byte
і (out of eleven) of the Disk Parameter contains the hexadecimal
і value CF in DOS 1.0 and DF in DOS 1.1 and later.
і DOS 1.0 24ms
ЪДДДДДДДДДДДДДґ DOS 1.1 26ms
і50:30-33 і Used by MODE command
і50:81і і number of floppies installed in the system?
і50:82і і first hard disk drive?
і50:83і і last hard disk drive?
і50:34-FF і Unknown - Reserved for DOS
АДДДДДДДДДДДДДБДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДД

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

ЪДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДї
і ROM BIOS Ъ model byte і
і copyright і Ъ submodel byte machine і
і date і і Ъ revision і
ГДДДДДДДДДДЕДДДДЕДДДДЕДДДДЕДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДДґ
і і 00 і 00 і 00 і AT&T 6300, Olivetti PC і
і 09/02/86 і FA і 00 і 00 і PS/2 Model 30 і
і 01/10/86 і FB і 00 і 00 і XT-2 (early) і
і 01/10/86 і FB і 00 і 01 і XT Model 089 і
і 05/09/86 і FB і 01 і 02 і XT-2 (revised) і
і 01/10/84 і FC і -- і -- і AT Model 099 (original) і
і 06/10/85 і FC і 00 і 01 і AT Model 239 6mHz (6.6 max governor) і
і 11/15/85 і FC і 01 і 00 і AT Model 339, 339 8mHz (8.6 max governor) і
і і FC і 01 і 00 і Compaq 386/16