@Tables and Formats used by DOS & BIOS :backup headers ^DOS BACKUP Control Information % BACKUPID.@@@ Format % Offset Size Description 00 byte Disk sequence flag: 00 indicates disk is not the last backup diskette FF indicates disk is the last backup diskette 01 word Floppy disk sequence number (Intel format) 03 word Backup year, four digits (Intel format) 05 byte Day of month (1-31) 06 byte Month of year (1-12) 07 dword System time if /T was specified (see ~FILE ATTRIBUTES~) 0B 117bytes Unused % Backup File Header % Offset Size Description 00 byte Disk sequence flag: 00 indicates disk is not the last backup diskette FF indicates disk is the last backup diskette 01 byte Floppy disk sequence number 02 3bytes Unused 05 64bytes Full pathname (without drive designator) 45 14bytes Unused 53 byte Length of file path name at offset 05 plus 1 54 44Bytes Unused :BIOS Parameter Block:BPB ^BPB - BIOS Parameter Block % Offset Size Description 00 word sector size in bytes 02 byte sectors per cluster (allocation unit size) 03 word number of reserved sectors 05 byte number of FATs on disk 06 word number of root directory entries (directory size) 08 word number of total sectors; if partition > 32Mb then set to zero and dword at 15h contains the actual count 0A byte media descriptor byte (see ~MEDIA DESCRIPTOR~) 0B word sectors per ~FAT~ % Additional/different fields for DOS 3.0+ 0D word sectors per track 0F word number of heads 11 word number of hidden sectors 15 11bytes reserved % Additional/different fields for DOS 4.0+ 15 dword number of total sectors if offset 8 is zero 19 6bytes reserved 1F word number of cylinders 21 byte device type 22 word device attributes - located in the boot sector at offset 0Bh - see ~BOOT SECTOR~ :Batch Control Block:BCB ^BCB - Batch Control Block (undocumented) ^DOS 2.x thru DOS 3.2 BCB Format % Offset Size Description 00 byte unknown 01 word if non-zero; segment of control block for active FOR 03 byte type of batch command 0 - normal batch command 1 - FOR-loop active 04 dword offset of next command to execute in batch file 07 word offset of variable %0 (batch file name) 09 9 words offset of %N batch file parameters, 0FFFFh indicates parameter is null 1C nbytes null terminated path and filename of the current batch file immediately followed by command line parameters. Each parameter %0-%9 plus a CR is appended and resulting string is null terminated. ^DOS 3.3 BCB Format % Offset Size Description 00 byte unknown 01 byte global echo switch, if exec'd by batch CALL-command 1 - turn ECHO ON on return to calling batch file 0 - turn ECHO OFF on return to calling batch file 02 word batch file BCD segment if executed via CALL if zero; batch file was called from command line if non-zero; batch file executed via CALL-command 04 word if non-zero; segment of control block for active FOR 06 byte type of batch command 0 - normal batch command 1 - FOR-loop active 07 dword offset of next command to execute in batch file 0B word offset of variable %0 (batch file name) 0D 9words offset of %N batch file parameters, 0FFFFh indicates parameter is null 1F nbytes null terminated path and filename of the current batch file immediately followed by command line parameters. Each parameter %0-%9 plus a CR is appended and resulting string is null terminated. - BCB length is variable and depends on the size and count of the parameters and fully qualified batch file name - the MCB for a BCB has a process Id of the transient portion of the latest COMMAND.COM - offsets displayed are relative to the BCB segment - SHIFT command changes the offsets of the parameters in the table at the offsets 0B0h thru 1Ch - BCB of DOS 3.3 is the same as earlier versions except 3 bytes were added after offset 0 - to find a BCB, locate the first block in the MCB chain belonging to COMMAND.COM (the second allocated block always belongs to COMMAND.COM). Then scan the ~MCB~ chain for a 64 byte block with the same owner ID as COMMAND.COM). This will be the BCB. :BIOS Data Area:BDA:BIOS memory:memory map ^BDA - BIOS Data Area - PC Memory Map % Address Size Description 00:00 256dwords Interrupt vector table 30:00 256bytes Stack area used during post and bootstrap 40:00 word COM1 port address 40:02 word COM2 port address 40:04 word COM3 port address 40:06 word COM4 port address 40:08 word LPT1 port address 40:0A word LPT2 port address 40:0C word LPT3 port address 40:0E word LPT4 port address (except PS/2) Extended BIOS Data Area segment (PS/2, see ~EBDA~) 40:10 2 bytes Equipment list flags (see ~INT 11~) ³7³6³5³4³3³2³1³0³ 40:10 (value in INT 11 register AL) ³ ³ ³ ³ ³ ³ ³ ÀÄ IPL diskette installed ³ ³ ³ ³ ³ ³ ÀÄÄ math coprocessor ³ ³ ³ ³ ÃÄÅÄÄÄ old PC system board RAM < 256K ³ ³ ³ ³ ³ ÀÄÄ pointing device installed (PS/2) ³ ³ ³ ³ ÀÄÄÄ not used on PS/2 ³ ³ ÀÄÁÄÄÄÄ initial video mode ÀÄÁÄÄÄÄÄÄÄ # of diskette drives, less 1 ³7³6³5³4³3³2³1³0³ 40:11 (value in INT 11 register AH) ³ ³ ³ ³ ³ ³ ³ ÀÄ 0 if DMA installed ³ ³ ³ ³ ÀÄÁÄÁÄÄ number of serial ports ³ ³ ³ ÀÄÄÄÄÄÄÄ game adapter ³ ³ ÀÄÄÄÄÄÄÄÄ not used, internal modem (PS/2) ÀÄÁÄÄÄÄÄÄÄÄÄ number of printer ports 40:12 byte PCjr: infrared keyboard link error count 40:13 word Memory size in Kbytes (see ~INT 12~) 40:15 byte Reserved 40:16 byte PS/2 BIOS control flags 40:17 byte Keyboard flag byte 0 (see ~KB FLAGS~) ³7³6³5³4³3³2³1³0³ keyboard flag byte 0 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ right shift key depressed ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ left shift key depressed ³ ³ ³ ³ ³ ÀÄÄÄÄÄ CTRL key depressed ³ ³ ³ ³ ÀÄÄÄÄÄÄ ALT key depressed ³ ³ ³ ÀÄÄÄÄÄÄÄ scroll-lock is active ³ ³ ÀÄÄÄÄÄÄÄÄ num-lock is active ³ ÀÄÄÄÄÄÄÄÄÄ caps-lock is active ÀÄÄÄÄÄÄÄÄÄÄ insert is active 40:18 byte Keyboard flag byte 1 (see ~KB FLAGS~) ³7³6³5³4³3³2³1³0³ keyboard flag byte ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ left CTRL key depressed ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ left ALT key depressed ³ ³ ³ ³ ³ ÀÄÄÄÄÄ system key depressed and held ³ ³ ³ ³ ÀÄÄÄÄÄÄ suspend key has been toggled ³ ³ ³ ÀÄÄÄÄÄÄÄ scroll lock key is depressed ³ ³ ÀÄÄÄÄÄÄÄÄ num-lock key is depressed ³ ÀÄÄÄÄÄÄÄÄÄ caps-lock key is depressed ÀÄÄÄÄÄÄÄÄÄÄ insert key is depressed 40:19 byte Storage for alternate keypad entry 40:1A word Offset from 40:00 to keyboard buffer head 40:1C word Offset from 40:00 to keyboard buffer tail 40:1E 32bytes Keyboard buffer (circular queue buffer) 40:3E byte Drive recalibration status ³7³6³5³4³3³2³1³0³ drive recalibration status ³ ³ ³ ³ ³ ³ ³ ÀÄÄ 1=recalibrate drive 0 ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1=recalibrate drive 1 ³ ³ ³ ³ ³ ÀÄÄÄÄ 1=recalibrate drive 2 ³ ³ ³ ³ ÀÄÄÄÄÄ 1=recalibrate drive 3 ³ ÀÄÁÄÁÄÄÄÄÄÄ unused ÀÄÄÄÄÄÄÄÄÄÄÄ 1=working interrupt flag 40:3F byte Diskette motor status ³7³6³5³4³3³2³1³0³ diskette motor status ³ ³ ³ ³ ³ ³ ³ ÀÄÄ 1=drive 0 motor on ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1=drive 1 motor on ³ ³ ³ ³ ³ ÀÄÄÄÄ 1=drive 2 motor on ³ ³ ³ ³ ÀÄÄÄÄÄ 1=drive 3 motor on ³ ÀÄÁÄÁÄÄÄÄÄÄ unused ÀÄÄÄÄÄÄÄÄÄÄÄ 1=write operation 40:40 byte Motor shutoff counter (decremented by ~INT 8~) 40:41 byte Status of last diskette operation (see ~INT 13,1~) ³7³6³5³4³3³2³1³0³ status of last diskette operation ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ invalid diskette command ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ diskette address mark not found ³ ³ ³ ³ ³ ÀÄÄÄÄÄ sector not found ³ ³ ³ ³ ÀÄÄÄÄÄÄ diskette DMA error ³ ³ ³ ÀÄÄÄÄÄÄÄ CRC check / data error ³ ³ ÀÄÄÄÄÄÄÄÄ diskette controller failure ³ ÀÄÄÄÄÄÄÄÄÄ seek to track failed ÀÄÄÄÄÄÄÄÄÄÄ diskette time-out 40:42 7 bytes NEC diskette controller status (see ~FDC~) 40:49 byte Current video mode (see ~VIDEO MODE~) 40:4A word Number of screen columns 40:4C word Size of current video regen buffer in bytes 40:4E word Offset of current video page in video regen buffer 40:50 8 words Cursor position of pages 1-8, high order byte=row low order byte=column; changing this data isn't reflected immediately on the display 40:60 byte Cursor ending (bottom) scan line (don't modify) 40:61 byte Cursor starting (top) scan line (don't modify) 40:62 byte Active display page number 40:63 word Base port address for active ~6845~ CRT controller 3B4h = mono, 3D4h = color 40:65 byte 6845 CRT mode control register value (port 3x8h) EGA/VGA values emulate those of the MDA/CGA 40:66 byte CGA current color palette mask setting (port 3d9h) EGA and VGA values emulate the CGA 40:67 dword CS:IP for 286 return from protected mode dword Temp storage for SS:SP during shutdown dword Day counter on all products after AT dword PS/2 Pointer to reset code with memory preserved 5 bytes Cassette tape control (before AT) 40:6C dword Daily timer counter, equal to zero at midnight; incremented by INT 8; read/set by ~INT 1A~ 40:70 byte Clock rollover flag, set when 40:6C exceeds 24hrs 40:71 byte BIOS break flag, bit 7 is set if ~Ctrl-Break~ was *ever* hit; set by ~INT 9~ 40:72 word Soft reset flag via Ctl-Alt-Del or JMP FFFF:0 1234h Bypass memory tests & CRT initialization 4321h Preserve memory 5678h System suspend 9ABCh Manufacturer test ABCDh Convertible POST loop ????h many other values are used during POST 40:74 byte Status of last hard disk operation (see ~INT 13,1~) 40:75 byte Number of hard disks attached 40:76 byte XT fixed disk drive control byte 40:77 byte Port offset to current fixed disk adapter 40:78 4 bytes Time-Out value for LPT1,LPT2,LPT3(,LPT4 except PS/2) 40:7C 4 bytes Time-Out value for COM1,COM2,COM3,COM4 40:80 word Keyboard buffer start offset (seg=40h,BIOS 10-27-82) 40:82 word Keyboard buffer end offset (seg=40h,BIOS 10-27-82) 40:84 byte Rows on the screen (less 1, EGA+) 40:85 word Point height of character matrix (EGA+) byte PCjr: character to be repeated if the typematic repeat key takes effect 40:86 byte PCjr: initial delay before repeat key action begins 40:87 byte PCjr: current Fn function key number byte Video mode options (EGA+) ³7³6³5³4³3³2³1³0³ Video mode options (EGA+) ³ ³ ³ ³ ³ ³ ³ ÀÄÄ 1=alphanumeric cursor emulation enabled ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1=video subsystem attached to monochrome ³ ³ ³ ³ ³ ÀÄÄÄÄ reserved ³ ³ ³ ³ ÀÄÄÄÄÄ 1=video subsystem is inactive ³ ³ ³ ÀÄÄÄÄÄÄ reserved ³ ÀÄÁÄÄÄÄÄÄÄ video RAM 00-64K 10-192K 01-128K 11-256K ÀÄÄÄÄÄÄÄÄÄÄ video mode number passed to ~INT 10~, function 0 40:88 byte PCjr: third keyboard status byte EGA feature bit switches, emulated on VGA ³7³6³5³4³3³2³1³0³ EGA feature bit switches (EGA+) ³ ³ ³ ³ ³ ³ ³ ÀÄÄ EGA SW1 config (1=off) ³ ³ ³ ³ ³ ³ ÀÄÄÄ EGA SW2 config (1=off) ³ ³ ³ ³ ³ ÀÄÄÄÄ EGA SW3 config (1=off) ³ ³ ³ ³ ÀÄÄÄÄÄ EGA SW4 config (1=off) ³ ³ ³ ÀÄÄÄÄÄÄ Input FEAT0 (ISR0 bit 5) after output on FCR0 ³ ³ ÀÄÄÄÄÄÄÄ Input FEAT0 (ISR0 bit 6) after output on FCR0 ³ ÀÄÄÄÄÄÄÄÄ Input FEAT1 (ISR0 bit 5) after output on FCR1 ÀÄÄÄÄÄÄÄÄÄ Input FEAT1 (ISR0 bit 6) after output on FCR1 40:89 byte Video display data area (MCGA and VGA) ³7³6³5³4³3³2³1³0³ Video display data area (MCGA and VGA) ³ ³ ³ ³ ³ ³ ³ ÀÄÄ 1=VGA is active ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1=gray scale is enabled ³ ³ ³ ³ ³ ÀÄÄÄÄ 1=using monochrome monitor ³ ³ ³ ³ ÀÄÄÄÄÄ 1=default palette loading is disabled ³ ³ ³ ÀÄÄÄÄÄÄ see table below ³ ³ ÀÄÄÄÄÄÄÄ reserved ³ ÀÄÄÄÄÄÄÄÄ 1=display switching enabled ÀÄÄÄÄÄÄÄÄÄ alphanumeric scan lines (see table below) % Bit7 Bit4 Scan Lines 0 0 350 line mode 0 1 400 line mode 1 0 200 line mode 1 1 reserved 40:8A byte Display Combination Code (DCC) table index (EGA+) 40:8B byte Last diskette data rate selected ³7³6³5³4³3³2³1³0³ last diskette data rate selected ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄ reserved ³ ³ ÀÄÁÄÄÄÄÄÄÄÄÄÄ last floppy drive step rate selected ÀÄÁÄÄÄÄÄÄÄÄÄÄÄÄ last floppy data rate selected % Data Rate Step Rate 00 500K bps 00 step rate time of 0C 01 300K bps 01 step rate time of 0D 10 250K bps 10 step rate time of 0A 11 reserved 11 reserved 40:8C byte Hard disk status returned by controller 40:8D byte Hard disk error returned by controller 40:8E byte Hard disk interrupt control flag(bit 7=working int) 40:8F byte Combination hard/floppy disk card when bit 0 set 40:90 4 bytes Drive 0,1,2,3 media state ³7³6³5³4³3³2³1³0³ drive media state (4 copies) ³ ³ ³ ³ ³ ÀÄÁÄÁÄÄÄ drive/media state (see below) ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ reserved ³ ³ ³ ÀÄÄÄÄÄÄÄ 1=media/drive established ³ ³ ÀÄÄÄÄÄÄÄ double stepping required ÀÄÁÄÄÄÄÄÄÄ data rate: 00=500K bps 01=300K bps 10=250K bps 11=reserved % Bits % 210 Drive Media State 000 360Kb diskette/360Kb drive not established 001 360Kb diskette/1.2Mb drive not established 010 1.2Mb diskette/1.2Mb drive not established 011 360Kb diskette/360Kb drive established 100 360Kb diskette/1.2Mb drive established 101 1.2Mb diskette/1.2Mb drive established 110 Reserved 111 None of the above 40:94 byte Track currently seeked to on drive 0 40:95 byte Track currently seeked to on drive 1 40:96 byte Keyboard mode/type ³7³6³5³4³3³2³1³0³ Keyboard mode/type ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ last code was the E1 hidden code ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ last code was the E0 hidden code ³ ³ ³ ³ ³ ÀÄÄÄÄÄ right CTRL key depressed ³ ³ ³ ³ ÀÄÄÄÄÄÄ right ALT key depressed ³ ³ ³ ÀÄÄÄÄÄÄÄ 101/102 enhanced keyboard installed ³ ³ ÀÄÄÄÄÄÄÄÄ force num-lock if Rd ID & KBX ³ ÀÄÄÄÄÄÄÄÄÄ last char was first ID char ÀÄÄÄÄÄÄÄÄÄÄ read ID in process 40:97 byte Keyboard LED flags ³7³6³5³4³3³2³1³0³ Keyboard LED flags ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ scroll lock indicator ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ num-lock indicator ³ ³ ³ ³ ³ ÀÄÄÄÄÄ caps-lock indicator ³ ³ ³ ³ ÀÄÄÄÄÄÄ circus system indicator ³ ³ ³ ÀÄÄÄÄÄÄÄ ACK received ³ ³ ÀÄÄÄÄÄÄÄÄ re-send received flag ³ ÀÄÄÄÄÄÄÄÄÄ mode indicator update ÀÄÄÄÄÄÄÄÄÄÄ keyboard transmit error flag 40:98 dword Pointer to user wait complete flag 40:9C dword User wait Time-Out value in microseconds 40:A0 byte RTC wait function flag ³7³6³5³4³3³2³1³0³ ~INT 15,86~ RTC wait function flag ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1= wait pending ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄ not used ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1=INT 15,86 wait time elapsed 40:A1 byte LANA DMA channel flags 40:A2 2 bytes Status of LANA 0,1 40:A4 dword Saved hard disk interrupt vector 40:A8 dword BIOS Video Save/Override Pointer Table address (see ~VIDEO TABLES~) 40:AC 8 bytes Reserved 40:B4 byte Keyboard NMI control flags (convertible) 40:B5 dword Keyboard break pending flags (convertible) 40:B9 byte Port 60 single byte queue (convertible) 40:BA byte Scan code of last key (convertible) 40:BB byte NMI buffer head pointer (convertible) 40:BC byte NMI buffer tail pointer (convertible) 40:BD 16bytes NMI scan code buffer (convertible) 40:CE word Day counter (convertible and after) 40:F0 16bytes Intra-Applications Communications Area (IBM Technical Reference incorrectly locates this at 50:F0-50:FF) % Address Size Description (BIOS/DOS Data Area) 50:00 byte Print screen status byte 00 = PrtSc not active, 01 = PrtSc in progress FF = error 50:01 3 bytes Used by BASIC 50:04 byte DOS single diskette mode flag, 0=A:, 1=B: 50:05 10bytes POST work area 50:0F byte BASIC shell flag; set to 2 if current shell 50:10 word BASICs default DS value (DEF SEG) 50:12 dword Pointer to BASIC ~INT 1C~ interrupt handler 50:16 dword Pointer to BASIC ~INT 23~ interrupt handler 50:1A dword Pointer to BASIC ~INT 24~ disk error handler 50:20 word DOS dynamic storage 50:22 14bytes DOS diskette initialization table (~INT 1E~) 50:30 4bytes MODE command 70:00 I/O drivers from IO.SYS/IBMBIO.COM ^The following map varies in size and locus 07C0:0 Boot code is loaded here at startup (31k mark) A000:0 EGA/VGA RAM for graphics display mode 0Dh & above B000:0 MDA RAM, Hercules graphics display RAM B800:0 CGA display RAM C000:0 EGA/VGA BIOS ROM (thru C7FF) C400:0 Video adapter ROM space C600:0 256bytes PGA communication area C800:0 16K Hard disk adapter BIOS ROM C800:5 XT Hard disk ROM format, AH=Drive, AL=Interleave D000:0 32K Cluster adapter BIOS ROM D800:0 PCjr conventionalsoftware cartridge address E000:0 64K Expansion ROM space (hardwired on AT+) 128K PS/2 System ROM (thru F000) F000:0 System monitor ROM PCjr: software cartridge override address F400:0 System expansion ROMs F600:0 IBM ROM BASIC (AT) F800:0 PCjr software cartridge override address FC00:0 BIOS ROM FF00:0 System ROM FFA6:E ROM graphics character table FFFF:0 ROM bootstrap code FFFF:5 8 bytes ROM date (not applicable for all clones) FFFF:E byte ROM machine id (see ~MACHINE ID~) :boot sector:boot record ^Boot Sector (since DOS 2.0) % Offset Size Description 00 3bytes jump to executable code 03 8bytes OEM name and version 0B word bytes per sector 0D byte sectors per cluster (allocation unit size) 0E word number of reserved sectors (starting at 0) 10 byte number of FAT's on disk 11 word number of root directory entries (directory size) 13 word number of total sectors (0 if partition > 32Mb) 15 byte media descriptor byte (see ~MEDIA DESCRIPTOR~) 16 word sectors per FAT 18 word sectors per track (DOS 3.0+) 1A word number of heads (DOS 3.0+) 1C word number of hidden sectors (DOS 3.0+) 20 dword (DOS 4+) number of sectors if offset 13 was 0 24 byte (DOS 4+) physical drive number 25 byte (DOS 4+) reserved 26 byte (DOS 4+) signature byte (29h) 27 dword (DOS 4+) volume serial number 2B 11bytes (DOS 4+) volume label 36 8bytes (DOS 4+) reserved - implementation format not guaranteed in all OEM DOS releases - BIOS expects a boot sector of 512 bytes - DOS 3.2 began reading BIOS Parameter Block (~BPB~) information from the boot sector, previous versions used only the media byte in FAT - DOS 4.x added offsets 20-3Dh and offset 20h determines the number of sectors if offset 13h is zero - hard disks have a master boot record and partition boot records; the master boot record and ~Disk Partition Table~ (DPT) share the same sector :Box Drawing Chars ^Box Drawing Characters 218 196 194 191 201 205 203 187 ÚÄÄÄÄÄÄÄÄÄÂÄÄÄÄ¿ ÉÍÍÍÍÍÍÍÍÍËÍÍÍÍ» 179 ³ 197 ³ ³ 179 186 º 206 º º 186 ³ \ ³ ³ º \ º º 195 ÃÄÄÄÄÄÄÄÄÄÅÄÄÄÄ´ 180 204 ÌÍÍÍÍÍÍÍÍÍÎÍÍÍ͹ 185 ³ ³ ³ º º º ÀÄÄÄÄÄÄÄÄÄÁÄÄÄÄÙ ÈÍÍÍÍÍÍÍÍÍÊÍÍÍͼ 192 196 193 217 200 205 202 188 214 196 210 183 213 205 209 184 ÖÄÄÄÄÄÄÄÄÄÒÄÄÄÄ· ÕÍÍÍÍÍÍÍÍÍÑÍÍÍ͸ 186 º 215 º º 186 179 ³ 216 ³ ³ 179 º \ º º ³ \ ³ ³ 199 ÇÄÄÄÄÄÄÄÄÄ×ÄÄÄĶ 182 198 ÆÍÍÍÍÍÍÍÍÍØÍÍÍ͵ 181 º º º ³ ³ ³ ÓÄÄÄÄÄÄÄÄÄÐÄÄÄĽ ÔÍÍÍÍÍÍÍÍÍÏÍÍÍ; 211 196 208 189 212 205 207 190 - see ~ASCII~ :code pages ^Code Page and Country Codes % Country Keyboard Valid Code % Country Code Code Pages Arabic 785 437 Australia 061 US 437,850 Belgium 032 BE 437,850 Canada (English) 001 US 437,850 Canada (French) 002 CF 863,850 Denmark 045 DK 865,850 Finland 358 SU 437,850 France 033 FR 437,850 Germany 049 GR 437,850 Hebrew 972 437 Italy 039 IT 437,850 Latin America 003 LA 437,850 Netherlands 031 NL 437,850 Norway 047 NO 865,850 Portugal 351 PO 860,850 Spain 034 SP 437,850 Sweden 046 SV 437,850 Switzerland (French) 041 SF 437,850 Switzerland (German) 041 SF 437,850 United Kingdom 044 UK 437,850 United States 001 US 437,850 - code pages are lookup tables containing the definition of one or more character sets - contain country specific information - implemented starting with DOS 3.3 :colors:color table ^Color Definitions % Definitions found in TURBO C's "conio.h" 0 - BLACK 4 - RED 8 - DARKGRAY C - LIGHTRED 1 - BLUE 5 - MAGENTA 9 - LIGHTBLUE D - LIGHTMAGENTA 2 - GREEN 6 - BROWN A - LIGHTGREEN E - YELLOW 3 - CYAN 7 - LIGHTGRAY B - LIGHTCYAN F - WHITE ³7³6³5³4³3³2³1³0³ AL ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ blue component of foreground color ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ green component of foreground color ³ ³ ³ ³ ³ ÀÄÄÄÄÄ red component of foreground color ³ ³ ³ ³ ÀÄÄÄÄÄÄ INTENSITY component of foreground color ³ ³ ³ ÀÄÄÄÄÄÄÄ blue component of background color ³ ³ ÀÄÄÄÄÄÄÄÄ green component of background color ³ ÀÄÄÄÄÄÄÄÄÄ red component of background color ÀÄÄÄÄÄÄÄÄÄÄ BLINKING of foreground character - see ~ANSI~ for ANSI color definitions :country codes:country info ^DOS Country Codes (DOS 2.x) % Offset Size Description 00 word Date and time format 0 = month day year, hh:mm:ss (USA) 1 = day month year, hh:mm:ss (Europe) 2 = year month day, hh:mm:ss (Japan) 02 2bytes ASCIIZ currency symbol 04 2bytes ASCIIZ thousands separator 06 2bytes ASCIIZ decimal separator 08 18bytes Reserved ^DOS Country Codes (DOS 3.0+) % Offset Size Description 00 word Date and time format 0 = month day year, hh:mm:ss (USA) 1 = day month year, hh:mm:ss (Europe) 2 = year month day, hh:mm:ss (Japan) 02 5bytes ASCIIZ currency symbol 07 2bytes ASCIIZ thousands separator 09 2bytes ASCIIZ decimal separator 0B 2bytes ASCIIZ date separator 0D 2bytes ASCIIZ time separator 0F byte Currency symbol format 0 = symbol leads, without space 1 = symbol follows, without space 2 = symbol leads, one space 3 = symbol follows, one space 4 = symbol replace decimal separator 10 byte Number of digits after decimal 11 byte Time format Bit 0 = 0 12 hour clock = 1 24 hour clock 12 dword Case map call address 16 2bytes ASCIIZ data list separator 18 10bytes Reserved - see also ~INT 21,38~ :disk partition table:partition table ^Disk Partition Table (Fixed disk boot record) % Offset Represents: (see format below) 01BE Partition 1 data table (16 bytes) 01CE Partition 2 data table (16 bytes) 01DE Partition 3 data table (16 bytes) 01EE Partition 4 data table (16 bytes) 01FE Signature (hex 55 AA, 2 bytes) % Offset from beginning of partition data shown above: % Offset Size Description 00 byte boot indicator 01 byte beginning sector head number 02 byte beginning sector (2 high bits of cylinder #) 03 byte beginning cylinder# (low order bits of cylinder #) 04 byte system indicator 05 byte ending sector head number 06 byte ending sector (2 high bits of cylinder #) 07 byte ending cylinder# (low order bits of cylinder #) 08 dword number of sectors preceding the partition 0B dword number of sectors in the partition % Boot indicator (BYTE) 00 - non-bootable partition 80 - bootable partition (one partition only) % System Indicator (BYTE) 00 - unknown operating system 01 - DOS with 12 bit FAT, 16 bit sector number 02 - XENIX 04 - DOS with 16 bit FAT, 16 bit sector number 05 - DOS Extended partition (DOS 3.3+) 06 - DOS 4.0 (Compaq 3.31), 32 bit sector number 51 - Ontrack extended partition 64 - Novell 75 - PCIX DB - CP/M FF - BBT % Signature Hex 55AA marks the end of valid boot sector. This is also required in each of the partition boot records. % Sector/Cylinder 2 bytes are combined to a word similar to INT 13: ³7³6³5³4³3³2³1³0³ 1st byte (sector) ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄ Sector offset within cylinder ÀÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄ High order bits of cylinder # ³7³6³5³4³3³2³1³0³ 2nd byte (cylinder) ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄ Low order bits of cylinder # - all partitions begin on sector 1 head 0, except the first partition which follows the disk's master boot record and begins in sector 2 - some of this information may vary with some variants of DOS 3.2 and DOS 3.3 that use their own sectoring scheme for large disks - see ~INT 21,32~ ~Disk Partition Table~ :device attributes ^Device Driver Attribute Values (brief) ³F³E³D³C³B³A-7³6³5³4³3³2³1³0³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄ 1 = character device is stdin ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ 1 = block dev supports generic IOCTL ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = character device is stdout ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ 1 = block dev supports generic IOCTL ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = current NUL device ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = current clock device ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÄÄÄÄÄ reserved by DOS ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄ 1 = supports Get/Set logical device ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄ reserved (must be zero) ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = supports removable media ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄ reserved (must be zero) ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = non-IBM format (block device) ³ ³ 1 = output until busy (char device) ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = supports IOCTL strings ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = character device, 0 = block device - true bit values are described, a false indicates opposite - see ~INT 21,44~ or IOCTL,n where "n" is an IOCTL function ^Device Driver Attribute Bit Values (detailed) 0 standard input device: used by character devices to tell DOS a character device driver is the standard input device. For block devices, a 1 indicates generic IOCTL supported 1 standard output device: used by character devices to tell DOS a character device driver is the standard output device. For block devices, a 1 indicates generic IOCTL supported 2 NUL attribute: used for character devices only. Tells DOS the character device driver is a NUL device. This bit is used by DOS to determine if the NUL device is being used. The NUL device cannot be reassigned. 3 clock device: set to 1 to tell DOS this is the new CLOCK$ device. 0B open/close removable media: set to 1 tells DOS the device driver can handle removable media. (DOS 3.x) 0D non-IBM format: for block devices, indicates the method the driver uses to determine media type. Set to 1 for drivers that use the BPB to determine media type, set to zero for drivers that use the media descriptor byte. For character devices (usually printers), set to 1 if the driver supports output until busy, set to 0 otherwise. 0E IOCTL bit: used with both character and block devices. Indicates if the device driver can handle control strings through the IOCTL. Zero if a device driver can't process control strings. If an attempt to send/receive an IOCTL control strings, is made without this bit set, an error code is returned. The IOCTL functions allow data to be sent to and from the driver without doing normal reads or writes. The device driver can use the data for information. It is up to the device to interpret the string, but the information must not be treated as a normal I/O request. Affects only IOCTL functions AL=2 and AL=5. 0F device type: used to indicate block or character device. :device command codes:device codes:device commands ^Device Command Codes (Device Request Header) % Code Function 0 INIT 1 MEDIA CHECK (block devices,character = NOP) 2 BUILD BPB (block devices,character = NOP) 3 IOCTL 4 INPUT (read) 5 NONDESTRUCTIVE INPUT NO WAIT (character devices) 6 INPUT STATUS (character devices) 7 INPUT FLUSH (character devices) 8 OUTPUT (write) 9 OUTPUT (write with verify) 10 OUTPUT STATUS (character devices) 11 OUTPUT FLUSH (character devices) 12 IOCTL OUTPUT 13 DEVICE OPEN (DOS 3.x) 14 DEVICE CLOSE (DOS 3.x) 15 REMOVABLE MEDIA (DOS 3.x) :device header ^Device Driver Header % Offset Size Description 00 dword pointer to next device header 04 word attribute (see ~DEVICE ATTRIBUTE~) 06 word pointer to device strategy routine 08 word pointer to device interrupt routine 0A 8bytes name/unit field - see ~INT 21,44~ and IOCTL,n where "n" is an IOCTL function :device request header ^Device Request Header Format % Offset Size Description 00 byte length in bytes of the request header 01 byte unit code; the sub-unit the operation is for (block devices); meaningless for character devices 02 word command code, (see ~DEVICE COMMANDS~) 04 8bytes reserved for DOS 0C nbytes request data (variable length) - see ~INT 21,44~ or ~DEVICE ATTRIBUTES~ or ~DEVICE CODES~ - see also IOCTL,n where "n" is an IOCTL function :device status ^Device Status Word The device status word is set to zero on entry and is set by the driver interrupt routine on return. ³15³14-10³9³8³7-0³ STATUS word ³ ³ ³ ³ ÀÄÄÄÄ Error return code (if bit 15=1) ³ ³ ³ ÀÄÄÄÄÄÄ Done bit, function completed ³ ³ ÀÄÄÄÄÄÄÄ Busy bit ³ ÀÄÄÄÄÄÄÄÄÄÄ Reserved ÀÄÄÄÄÄÄÄÄÄÄÄÄÄ Error flag bits 0-7 have error code % Error return codes 00 Write protect violation 01 Unknown unit 02 Device not ready 03 Unknown command 04 CRC error 05 Bad drive request structure length 06 Seek error 07 Unknown media 08 Sector not found 09 Printer out of paper 0A Write fault 0B Read fault 0C General failure 0D Reserved 0E Reserved 0F Invalid disk change :directory format ^DIRECTORY - DOS Directory Structure % Byte Description 00 Filename status: 00 = Filename never used 05 = First character of filename is E5 E5 = File has been erased 2E = This is a subdirectory entry 00-07 Filename, left justified 08-0A Filename extension, left justified 0B File's attribute: ³7³6³5³4³3³2³1³0³ byte 0B ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ read only ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ hidden ³ ³ ³ ³ ³ ÀÄÄÄÄÄ system ³ ³ ³ ³ ÀÄÄÄÄÄÄ volume label ³ ³ ³ ÀÄÄÄÄÄÄÄ subdirectory ³ ³ ÀÄÄÄÄÄÄÄÄ archive ÀÄÁÄÄÄÄÄÄÄÄÄ unused 0C-15 Reserved by DOS 16-17 Time the file was created or last updated: ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³ 17,16 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄ seconds/2 ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ minutes ÀÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ hours 18-19 Date the file was created or last updated: ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³ 19,18 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄ day 1-31 ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ month 1-12 ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ year + 1980 1A-1B Starting cluster number of the first file cluster 1C-1F File size in bytes (low order first) :DBT:Disk Base Table ^DBT - Disk Base Table (BIOS INT 13) % Offset Size Description 00 byte specify byte 1; step-rate time, head unload time 01 byte specify byte 2; head load time, DMA mode 02 byte timer ticks to wait before disk motor shutoff 03 byte bytes per sector code: 0 - 128 bytes 2 - 512 bytes 1 - 256 bytes 3 - 1024 bytes 04 byte sectors per track (last sector number) 05 byte inter-block gap length/gap between sectors 06 byte data length, if sector length not specified 07 byte gap length between sectors for format 08 byte fill byte for formatted sectors 09 byte head settle time in milliseconds 0A byte motor startup time in eighths of a second :DTA:Disk Transfer Area ^DTA - Disk Transfer Area (partially undocumented) DTA contains data, of which the first 21 bytes (00-15h) are known as being "reserved for DOS use on subsequent find next calls" % Offset Size Description 00 byte attribute of search (undocumented) 01 byte drive used in search (undocumented) 02 11bytes search name used (undocumented) 0D word directory entry number (0 based, DOS 3.x+, undoc.) 0F word starting cluster number of current directory zero for root directory (DOS 3.x+, undocumented) 11 word reserved (undocumented) 13 word starting cluster number of current directory zero for root directory (DOS 2.x+, undocumented) 15 byte attribute of matching file 16 word file time (see ~FILE ATTRIBUTES~) 18 word file date (see FILE ATTRIBUTES) 1A word file size 1E 13bytes ASCIIZ filename and extension in the form NAME.EXT with blanks stripped - fields of DTA change dependent upon function call in progress - the ~DTA~ cannot span a 64K segment boundary - for compatibility with CP/M the default DTA is at offset 80h in the ~PSP~; this area is also used for the command tail. To avoid collision, set another DTA (INT 21,1A) or preserve the command tail before using ~FCB~ function calls - see ~INT 21,4E~ ~INT 21,1A~ ~INT 21,2F~ :DOS error codes:extended errors ^DOS Error Codes Of the following error codes, only error codes 1-12 are returned in AX upon exit from interrupt 21 or 24; The rest are obtained by issuing the "get extended error" function call; see ~INT 21,59~ 01 Invalid function number 02 File not found 03 Path not found 04 Too many open files (no handles left) 05 Access denied 06 Invalid handle 07 Memory control blocks destroyed 08 Insufficient memory 09 Invalid memory block address 0A Invalid environment 0B Invalid format 0C Invalid access mode (open mode is invalid) 0D Invalid data 0E Reserved 0F Invalid drive specified 10 Attempt to remove current directory 11 Not same device 12 No more files 13 Attempt to write on a write-protected diskette 14 Unknown unit 15 Drive not ready 16 Unknown command 17 CRC error 18 Bad request structure length 19 Seek error 1A Unknown media type 1B Sector not found 1C Printer out of paper 1D Write fault 1E Read fault 1F General failure 20 Sharing violation 21 Lock violation 22 Invalid disk change 23 FCB unavailable 24 Sharing buffer overflow 25 Reserved 26 Unable to complete file operation (DOS 4.x) 27-31 Reserved 32 Network request not supported 33 Remote computer not listening 34 Duplicate name on network 35 Network name not found 36 Network busy 37 Network device no longer exists 38 NetBIOS command limit exceeded 39 Network adapter error 3A Incorrect network response 3B Unexpected network error 3C Incompatible remote adapter 3D Print queue full 3E No space for print file 3F Print file deleted 40 Network name deleted 41 Access denied 42 Network device type incorrect 43 Network name not found 44 Network name limit exceeded 45 NetBIOS session limit exceeded 46 Temporarily paused 47 Network request not accepted 48 Print or disk redirection is paused 49-4F Reserved 50 File already exists 51 Reserved 52 Cannot make directory entry 53 Fail on INT 24 54 Too many redirections 55 Duplicate redirection 56 Invalid password 57 Invalid parameter 58 Network device fault 59 Function not supported by network (DOS 4.x) 5A Required system component not installed (DOS 4.x) ^DOS Error Code/Classes % Error Classes 01 Out of resource, out of space, channel, etc 02 Temporary situation, not an error, ex: file lock 03 Authorization, permission denied 04 Internal, system detected internal error 05 Hardware failure, serious problem related to hardware 06 System failure, ex: invalid configuration 07 Application error, inconsistent request 08 Not found, file/item not found 09 Bad format, file/item in invalid format 0A Locked, file/item interlocked 0B Media failure, ECC/CRC error, wrong or bad disk 0C Already exists, collision with existing item 0D Unknown, classification doesn't exist or is inappropriate ^DOS Error Code/Action Codes and Locus % Error Action Codes (in BL) 01 retry, attempt a few more times and re-prompt 02 delay retry, retry a few more times after a pause 03 re-enter input, prompt user to re-enter input 04 abort with cleanup, orderly abort and shutdown 05 immediate abort, exit immediately without cleanup 06 ignore error 07 user intervention, retry after user fixes the problem % Error Locus (in CH) 01 unknown 02 block device 03 network 04 serial device 05 memory :DOS versions:version ^VERSION - Versions of DOS % Version Date Changes PC-DOS 1.0 Oct 1981 original release, single sided drive PC-DOS 1.1 Jun 1982 bugfix, double sided drive support MS-DOS 1.25 Jun 1982 for early compatibles PC-DOS 2.0 Mar 1983 PC/XT, added (hard drive &UNIX features) PC-DOS 2.1 Oct 1983 PCjr & portable mods, fixes for 2.0 MS-DOS 2.11 Oct 1983 compatible equivalent to 2.1 PC-DOS 3.0 Aug 1984 support for 1.2 Mb drive (AT) PC-DOS 3.1 Nov 1984 added network support, fixes for 3.0 MS-DOS 2.25 Oct 1985 compatible; foreign language support PC-DOS 3.2 Jul 1986 720k 3«" drive support for Convertible MS-DOS 3.2 Jul 1986 MS-DOS 3.21 May 1987 MS-DOS 3.3 Jul 1987 PC-DOS 3.3 Apr 1987 PS/2, 1.44 disk support, mult. partitions MS-DOS 3.30a Feb 1988 CPQ-DOS 3.31 Oct 1988 Compaq DOS for disk partitions > 32MB PC-DOS 4.00 Aug 1988 Larger DOS partitions, EMS support (bugs) MS-DOS 4.00 Oct 1988 MS-DOS 4.01 Nov 1988 MS-DOS 4.01a Apr 1989 PC-DOS 4.01 ??? ???? Fixes for major bugs in 4.0 - release dates vary between OEM versions - IBM was supposedly responsible for most changes in DOS 4.x - DOS 4.01 reports version 4.0, except in some vendor versions - DOS 5.0 is primarily a Microsoft developed version :drive parameter table:disk parameter table:DPB:DPT ^DPT/DPB - Drive Parameter Table / Disk Parameter Block % Offset Size Description 00 byte drive (0 = A, 1 = B) 01 byte unit within device, usually equals drive (ramdisk=0) 02 word bytes per sector 04 byte sectors per cluster minus 1 05 byte sectors per cluster (times to shift left or x2) 06 word number of sectors before FAT (boot sectors) 08 byte number of ~FAT~ copies 09 word number of root directory entries 0B word number of first data sector 0D word total number of clusters plus 1 0F byte number of sectors used by first FAT % The following fields are DOS version dependant 10 word number of first sector in root directory 12 dword far pointer to current disk device header 16 byte media descriptor byte (see ~MEDIA DESCRIPTOR~) 17 byte zero if disk accessed, (default=FF, must rebuild ~DPB~) 18 dword far pointer to next drive parameter table; offset is set to FFFFh if last block in chain 1C word current directory cluster number; 0=root 1E 64bytes ASCIIZ current working directory ^Fields differing in DOS 3.x % Offset Size Description 1C word starting cluster for free space search 1E 64bytes number of free clusters; FFFFh = unknown ^Fields differing in DOS 4.x % Offset Size Description 11 word first sector of root directory 13 dword far pointer to current disk device header 17 byte media descriptor byte (see ~MEDIA DESCRIPTOR~) 18 byte zero if disk accessed, (default=FF, must rebuild ~DPB~) 19 dword pointer to next drive parameter table; offset is set to FFFFh if last block in chain 1D word starting cluster for free space search 1F word number of free clusters, FFFFh = unknown - ~INT 21,32~ which is used to read this data resets accessed byte at offset 17h or 18h (depending on DOS version) - dword at offset 12h & 13h aren't supported in OS/2 compatability box - sector references are DOS logical sectors - see ~Disk Base Table~ ~BPB~ ~INT 21,1F~ ~INT 21,32~ :drive status data:disk status data:diskette status data ^Drive Status Bytes Found in BIOS Data Area % Drive recalibration status (at 40:3E) ³7³6³5³4³3³2³1³0³ byte at 40:3E ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1=recalibrate drive 0 ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1=recalibrate drive 1 ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1=recalibrate drive 2 ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1=recalibrate drive 3 ³ ÀÄÁÄÁÄÄÄÄÄÄÄ unused ÀÄÄÄÄÄÄÄÄÄÄÄÄ 1=working interrupt flag % Diskette motor status ³7³6³5³4³3³2³1³0³ byte at 40:3F ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1=drive 0 motor on ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1=drive 1 motor on ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1=drive 2 motor on ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1=drive 3 motor on ³ ÀÄÁÄÁÄÄÄÄÄÄÄ unused ÀÄÄÄÄÄÄÄÄÄÄÄÄ 1=write operation % Disk Status Byte ³7³6³5³4³3³2³1³0³ byte at 40:41 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ invalid diskette command ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ diskette address mark not found ³ ³ ³ ³ ³ ÀÄÄÄÄÄ sector not found ³ ³ ³ ³ ÀÄÄÄÄÄÄ diskette DMA error ³ ³ ³ ÀÄÄÄÄÄÄÄ CRC check / data error ³ ³ ÀÄÄÄÄÄÄÄÄ diskette controller failure ³ ÀÄÄÄÄÄÄÄÄÄ seek to track failed ÀÄÄÄÄÄÄÄÄÄÄ diskette time-out % Last diskette data rate selected ³7³6³5³4³3³2³1³0³ byte at 40:8B ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄ step rate time selected (see below) ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ data rate selected (see below) % Bits % 76 Diskette Data Rate Selected 00 500K bps 01 300K bps 10 250K bps 11 reserved % Bits % 54 Diskette Step Rate Time Selected 00 step rate time of 0C 01 step rate time of 0D 10 step rate time of 0A 11 reserved % Media state for fixed drives (bytes at 40:90-93) ³7³6³5³4³3³2³1³0³ bytes at 40:90-40:93 ³ ³ ³ ³ ³ ÀÄÁÄÁÄÄÄ reserved (set to 1) ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄ reserved ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄ 0=media/drive unestablished ³ ³ ÀÄÄÄÄÄÄÄÄÄÄ reserved ÀÄÁÄÄÄÄÄÄÄÄÄÄÄ data rate (see below) % Bits % 76 Fixed Disk Data Rate Selected 00 500K bps 01 reserved 10 250K bps 11 reserved - not all OEM's implemented these bytes identically. Some are also AT specific. :EXE file header:.EXE ^.EXE - DOS EXE File Structure % Offset Size Description 00 word "MZ" - Link file .EXE signature (Mark Zbikowski?) 02 word length of image mod 512 04 word size of file in 512 byte pages 06 word number of relocation items following header 08 word size of header in 16 byte paragraphs, used to locate the beginning of the load module 0A word min # of paragraphs needed to run program 0C word max # of paragraphs the program would like 0E word offset in load module of stack segment (in paras) 10 word initial SP value to be loaded 12 word negative checksum of pgm used while by EXEC loads pgm 14 word program entry point, (initial IP value) 16 word offset in load module of the code segment (in paras) 18 word offset in .EXE file of first relocation item 1A word overlay number (0 for root program) - relocation table and the program load module follow the header - relocation entries are 32 bit values representing the offset into the load module needing patched - once the relocatable item is found, the CS register is added to the value found at the calculated offset % Registers at load time of the EXE file are as follows: AX: contains number of characters in command tail, or 0 BX:CX 32 bit value indicating the load module memory size DX zero SS:SP set to stack segment if defined else, SS = CS and SP=FFFFh or top of memory. DS set to segment address of EXE header ES set to segment address of EXE header CS:IP far address of program entry point, (label on "END" statement of program) :EBDA:extended BIOS ^EBDA - Extended BIOS Data Area EBDA (PS/2) % Offset Size Description 00 word number of bytes allocated to EBDA in Kbytes 01-21 21bytes reserved 22 dword device driver far call pointer 26 byte pointing device flag (1st byte, see below) 27 byte pointing device flag (2nd byte, see below) 28-2F 8 bytes reserved % Pointing Device Flag Byte 1 ³7³6³5³4³3³2³1³0³ Offset 26 ³ ³ ³ ³ ³ ÀÄÁÄÁÄÄÄ index count ³ ³ ³ ³ ÀÄÄÄÄÄÄÄÄ reserved (0) ³ ³ ³ ÀÄÄÄÄÄÄÄÄÄ error ³ ³ ÀÄÄÄÄÄÄÄÄÄÄ acknowledge ³ ÀÄÄÄÄÄÄÄÄÄÄÄ resend ÀÄÄÄÄÄÄÄÄÄÄÄÄ command in progress % Pointing Device Flag Byte 2 ³7³6³5³4³3³2³1³0³ Offset 27 ³ ³ ³ ³ ³ ÀÄÁÄÁÄÄÄ package size ³ ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄ reserved ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ device driver far call flag - EBDA is located in highest memory just under 640K on PS/2 - word at ~BIOS Data Area~ 40:0E is segment address of EBDA :FAT:File Allocation Table ^FAT - File Allocation Table % 12 Bit Meaning 16 Bit 000 free space 0000 FF1-FF7 bad track marking FFF1-FFF7 FF8-FFE may be used to mark end of a file chain FFF8-FFFE FFF standard marker for end of a file chain FFFF - the FAT is implemented as an array containing a linked list for each file; the files directory entry has a pointer to the first cluster which contains the cluster number of the next cluster in the chain until the pointer contained is FFFh (12 bit FAT) and FFFFh (16 bit FAT) marking end of file - DOS maintains two copies of the FAT, but does not use the second copy for anything other than a mirror image of the first; CHKDSK doesn't even read the second FAT - disks with FF1h clusters and above use 16 bit FAT tables, disk with less use 12 bit FAT tables - DOS 4.x did not change the size of the cluster number as some suggest, but instead increased the size of the sector number - bytes 0 of the FAT contains the Media Descriptor Byte ^Calculating 12 bit FAT Entries 1. Get starting cluster from directory entry. 2. Multiply the cluster number just used by 1.5 3. The whole part of the product is the offset into the FAT, of the entry that maps to the cluster in the directory. This entry contains the number of the next cluster. 4. Move the word at the calculated FAT into a register. 5. If the last cluster used was an even number, keep the low order 12 bits of the register, otherwise, keep the high order 12 bits. 6. If the resultant 12 bits are (0FF8h-0FFFh) no more clusters are in the file. Otherwise, the next 12 bits contain the cluster number of the next cluster in the file. ^Calculating 16 Bit FAT Entries 1. Get the starting cluster of the file from the directory. 2. Multiply the cluster number found by 2. 3. Load the word at the calculated FAT offset into a register. 4. If the 16 bits are (0FFF8h-0FFFFh) no more clusters are in the file. Otherwise, the 16 bits contain the cluster number of the next cluster in the file. To convert the cluster to a logical sector number (relative sector, similar to that used by DEBUG, int 25h and 26h): 1. Subtract 2 from the cluster number 2. Multiply the result by the number of sectors per cluster. 3. Add the logical sector number of the beginning of the data area. - see ~MEDIA DESCRIPTOR~ :FCB:File Control Block ^FCB - Standard DOS File Control Block % Offset Size Description -7 byte if FF this is an extended FCB Ø -6 5bytes reserved Ø -1 byte file attribute if extended FCB Ø 00 byte drive number (0 for default drive, 1=A:, 2=B:, ...) 01 8bytes filename, left justified with trailing blanks 09 3bytes filename extension, left justified w/blanks 0C word current block number relative to beginning of the file, starting with zero 0E word logical record size in bytes 10 dword file size in bytes 14 word date the file was created or last updated ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³ 15,14 (Intel reverse order) ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄ day 1-31 ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ month 1-12 ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ year + 1980 16 word time of last write ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³ 17,16 (Intel reverse order) ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÄ secs in 2 second increments ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄ minutes (0-59) ÀÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ hours (0-23) 18 8bytes see below for version specific information Ø 1A dword address of device header if character device Ø 20 byte current relative record number within current BLOCK 21 dword relative record number relative to the beginning of the file, starting with zero; high bit omitted if record length is 64 bytes ^DOS 2.x Values for reserved fields at offsets 18h-1Ah Ø % Offset Size Description 18 byte ³7³6³5³4³3³2³1³0³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄ unknown ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = open ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 1 = logical device 19 word starting cluster number Ø ^DOS 3.x Values for reserved fields at offsets 18h-19h Ø % Offset Size Description 18 byte System File Table (SFT) entry for file Ø 19 byte attributes Ø ³7³6³5³4³3³2³1³0³ attributes ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄ unknown ÀÄÁÄ share status 00 = SHARE not loaded block device 01 = SHARE not loaded characted device 10 = SHARE loaded, remote file 11 = SHARE loaded local file ^DOS 3.x with SHARE, local file reserved offsets 1Ah-1Eh Ø % Offset Size Description 1A word starting cluster number 1C word offset within SHARE of sharing record 1E byte file attribute ^DOS 3.x with SHARE, remote file reserved offsets 1Ah-1Eh Ø % Offset Size Description 1A word sector number containing directory entry 1C word last cluster accessed relative to beginning of file 1E byte absolute cluster number of last cluster accessed ^DOS 3.x without SHARE reserved offsets 1Ah-1Fh Ø % Offset Size Description 1A byte ((device attribute word low byte) & 0Ch) || (open mode) 1B word starting cluster number 1D word sector number containing directory entry 1F byte number of directory entry within sector % The following are FCB related DOS functions: ~INT 21,F~ Open file using FCB ~INT 21,10~ Close file using FCB ~INT 21,11~ Search for first entry using FCB ~INT 21,12~ Search for next entry using FCB ~INT 21,13~ Delete file using FCB ~INT 21,14~ Sequential read using FCB ~INT 21,15~ Sequential write using FCB ~INT 21,16~ Create a file using FCB ~INT 21,17~ Rename file using FCB ~INT 21,21~ Random read using FCB ~INT 21,22~ Random write using FCB ~INT 21,23~ Get file size using FCB ~INT 21,24~ Set relative record field for FCB ~INT 21,27~ Random block read using FCB ~INT 21,28~ Random block write using FCB ~INT 21,29~ Parse filename for FCB Ø see ~Bibliography~ reference to "Undocumented DOS" - see ~XFCB~ ~INT 21,52~ :file attributes ^DOS File Attributes % Directory Attribute Flags ³7³6³5³4³3³2³1³0³ Directory Attribute Flags ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = read only ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = hidden ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = system ³ ³ ³ ³ ÀÄÄÄÄÄÄ 1 = volume label (exclusive) ³ ³ ³ ÀÄÄÄÄÄÄÄ 1 = subdirectory ³ ³ ÀÄÄÄÄÄÄÄÄ 1 = archive ÀÄÁÄÄÄÄÄÄÄÄÄ unused % Directory Time Format ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³ Directory Time Format ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÄÄ seconds (2 second increments) ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄ minutes (0-59) ÀÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ hours (0-23) % Directory Date Format ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³ Directory Date Format ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄÄÄ Day (1-31) ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄ Month (1-12) ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Year (less 1980) - with respect to the ~findfirst~() and ~findnext~() functions normal files are always included along with the requested attributes except when the LABEL attribute is requested. It's up to the programmer to determine which files are match the requested attributes. :file handles:default handles:handles ^DOS Default/Predefined File Handles 0 - Standard Input Device - can be redirected (STDIN) 1 - Standard Output Device - can be redirected (STDOUT) 2 - Standard Error Device - can be redirected (STDERR) 3 - Standard Auxiliary Device (STDAUX) 4 - Standard Printer Device (STDPRN) %See the following INT 21h Handle related function calls: ~INT 21,3C~ Create file using handle ~INT 21,3D~ Open file using handle ~INT 21,3E~ Close file using handle ~INT 21,3F~ Read file or device using handle ~INT 21,40~ Write file or device using handle ~INT 21,41~ Delete file ~INT 21,42~ Move file pointer using handle ~INT 21,43~ Change file mode ~INT 21,45~ Duplicate file handle ~INT 21,46~ Force duplicate file handle ~INT 21,56~ Rename file ~INT 21,57~ Get/set file date and time using handle ~INT 21,5A~ Create temporary file (3.x+) ~INT 21,5B~ Create new file (3.x+) ~INT 21,67~ Set handle count (3.3+) ~INT 21,68~ Flush buffer (3.3+) - STDIN, STDOUT and STDERR can be redirected - maximum number of files available to all DOS processes at one time is defined by the FILES=N statement of ~CONFIG.SYS~ - maximum number of files available to an application is N-3 where N is derived from the CONFIG.SYS FILES=N statement minus the count of handles used by other processes - ~INT 21,67~ can be used in DOS 3.3+ to increase the number of file handles for an application to greater than 20; the max handle count is still limited by the value of FILES= in CONFIG.SYS file - An application can increase the maximum allowed file handles in DOS 3.0-3.2 by copying the open file table located through offset 34h in the ~PSP~ to another location. All unopened slots must be initialized to FF and the values at PSP offsets 32h and 34h must be updated to reflect the new values. - see ~SFT~ ~INT 21~ ~INT 21,52~ ~INT 21,67~ :float formats:floating point:real numbers ^Floating Point Formats % IEEE 4 byte real 31 30 23 22 0 ÚÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³s³ 8 bits ³msb 23 bit mantissa lsb³ ÀÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ mantissa ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ biased exponent (7fh) ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ sign bit % IEEE 8 byte real 63 62 52 51 0 ÚÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³s³ 11 bits ³msb 52 bit mantissa lsb³ ÀÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ mantissa ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ biased exponent (3FFh) ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ sign bit % Microsoft 4 byte real 31 24 23 22 0 ÚÄÄÄÄÄÄÄÄÂÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ 8 bits ³s³msb 23 bit mantissa lsb³ ÀÄÄÄÄÄÄÄÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ mantissa ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ sign bit ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ biased exponent (81h) % Microsoft 8 byte real (see note below) 63 56 55 54 0 ÚÄÄÄÄÄÄÄÂÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ 8bits ³s³msb 52 bit mantissa lsb³ ÀÄÄÄÄÄÄÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄ mantissa ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ sign bit ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ biased exponent (401h, see below) % IEEE 10 byte real (temporary real) 79 78 64 63 62 0 ÚÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³s³ 15 bits ³1³msb 63 bit mantissa lsb³ ÀÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³ ³ ³ ÀÄÄÄÄÄ mantissa ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ first mantissa bit ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ biased exponent (3FFFh) ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ sign bit % Turbo Pascal 6 byte real 47 40 39 38 0 ÚÄÄÄÄÄÄÄÄÂÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ 8 bits ³s³msb 39 bit mantissa lsb³ ÀÄÄÄÄÄÄÄÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ³ ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄ mantissa ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ sign bit ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ biased exponent (80h) % Microsoft Fortran Complex number ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ Float Real component ³ Float Imaginary component ³ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ (each component is either 8 or 16 byte IEEE real) - sign bit representation: 0 is positive and 1 is negative - in all float formats except the IEEE 10 byte real, the mantissa is stored without most significant bit; since the state of this bit is known to be set, it is not included and the exponent is adjusted accordingly - all formats use binary float representation - memory representation uses 80x86 reverse byte/word order. - Microsoft languages use the IEEE real formats; BASIC is the only normal user of the Microsoft float format - Microsoft 8 byte real format has not been verified; several Microsoft publications show an 8 bit exponent instead of 11 bits and state the BIAS is 401h; the discrepancy is that 8 bits can't hold the value 401h (requires 11 bits) % True exponent is the exponent value minus the following bias: 81h for Microsoft 4 byte real 401h for Microsoft 8 byte real 7Fh for IEEE 4 byte real 3FFh for IEEE 8 byte real 80h for Turbo Pascal 6 byte real % Size Range Significant digits 4 byte real 8.43x10E-37 to 3.37x10E38 6-7 8 byte real 4.19x10E-307 to 1.67x10E308 15-16 10 byte real 3.4x10E-4932 to 1.2x10E4932 19 - see ~dmsbintoieee~() ~dieeetomsbin~() ~NUMERIC RANGES~ :floppy formats:disk formats ^Common Floppy Disk Formats % Supporting ÚÄÄÄÄÄSectorsÄÄÄÄ¿ Entries % Disk DOS per per per per per Total % Type Vers Sides Trks TRK FAT DIR Cluster DIR Sectors ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 5¬ 160k (1.0) 1 (40) 8 1 4 1 64 320 5¬ 320k (1.1) 2 (40) 8 1 7 2 112 640 5¬ 180k (2.0) 1 (40) 9 2 4 1 64 360 5¬ 360k (2.0) 2 (40) 9 2 7 2 112 720 5¬ 1.2M (3.0) 2 (80) 15 7 14 1 224 2400 3« 720k (3.2) 2 (80) 9 3 7 2 112 1440 3« 1.44M (3.3) 2 (80) 18 9 14 1 224 2880 :ID bytes:machine identificatn ^Machine Identification Byte % Model Sub-Model Machine FF ?? Original IBM PC 4/24/81 ?? IBM PC 10/19/81 ?? IBM PC 10/27/82 FE ?? IBM XT (Original) ?? IBM portable PC ?? Compaq DeskPro FD ?? PCjr FC ?? IBM AT (6 MHz) 01 IBM AT 3x9 (8 MHz) 02 IBM XT 286 04 IBM PS/2 Model 50 05 IBM PS/2 Model 60 0B IBM PS/1 FB 00 IBM 256/640K XT (aka XT/2) FA 00 IBM PS/2 Model 30 01 IBM PS/2 Model 25 F9 00 IBM PC Convertible F8 00 IBM PS/2 Model 80 (16 MHz) 01 IBM PS/2 Model 80 (20 MHz) 04 IBM PS/2 Model 70 (20 MHz) 09 IBM PS/2 Model 70 (16 MHz) B6 ?? Hewlett Packard 110 9A ?? Compaq Plus 86 XT (BIOS 11/82+) & AT (BIOS 1/84+) (see note) 80 PC & PCjr (see note) 2D ?? Compaq PC - found at memory location F000:FFFE or via INT 15,C0 - model values of 80 & 86 are returned by BIOS versions previous to the PS/2 but after the BIOS dates marked - see ~INT 15,C0~ :KB flags:keyboard flags ^Keyboard Flags Bytes 0 and 1 ³7³6³5³4³3³2³1³0³ 40:17 Keyboard Flags Byte 0 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ right shift key depressed ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ left shift key depressed ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ CTRL key depressed ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ ALT key depressed ³ ³ ³ ÀÄÄÄÄÄÄÄÄ scroll-lock is active ³ ³ ÀÄÄÄÄÄÄÄÄÄ num-lock is active ³ ÀÄÄÄÄÄÄÄÄÄÄ caps-lock is active ÀÄÄÄÄÄÄÄÄÄÄÄ insert is active ³7³6³5³4³3³2³1³0³ 40:18 Keyboard Flags Byte 1 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ left CTRL key depressed ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ left ALT key depressed ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ system key depressed and held ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ suspend key has been toggled ³ ³ ³ ÀÄÄÄÄÄÄÄÄ scroll lock key is depressed ³ ³ ÀÄÄÄÄÄÄÄÄÄ num-lock key is depressed ³ ÀÄÄÄÄÄÄÄÄÄÄ caps-lock key is depressed ÀÄÄÄÄÄÄÄÄÄÄÄ insert key is depressed ^Keyboard Flags Bytes 2 and 3 ³7³6³5³4³3³2³1³0³ 40:97 LED Indicator Flags ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ scroll lock indicator ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ num-lock indicator ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ caps-lock indicator ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ circus system indicator ³ ³ ³ ÀÄÄÄÄÄÄÄÄ ACK received ³ ³ ÀÄÄÄÄÄÄÄÄÄ re-send received flag ³ ÀÄÄÄÄÄÄÄÄÄÄ mode indicator update ÀÄÄÄÄÄÄÄÄÄÄÄ keyboard transmit error flag ³7³6³5³4³3³2³1³0³ 40:96 Keyboard Mode/Type ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ last code was the E1 hidden code ³ ³ ³ ³ ³ ³ ÀÄÄÄÄÄ last code was the E0 hidden code ³ ³ ³ ³ ³ ÀÄÄÄÄÄÄ right CTRL key depressed ³ ³ ³ ³ ÀÄÄÄÄÄÄÄ right ALT key depressed ³ ³ ³ ÀÄÄÄÄÄÄÄÄ 101/102 enhanced keyboard installed ³ ³ ÀÄÄÄÄÄÄÄÄÄ force num-lock if Rd ID & KBX ³ ÀÄÄÄÄÄÄÄÄÄÄ last char was first ID char ÀÄÄÄÄÄÄÄÄÄÄÄ read ID in process - see ~INT 9~ ~BDA~ :make codes:break codes ^INT 9 - Hardware Keyboard Make/Break Codes % Key Make Break Key Make Break Backspace 0E 8E F1 3B BB Caps Lock 3A BA F2 3C BC Enter 1C 9C F3 3D BD Esc 01 81 F4 3E BE Left Alt 38 B8 F7 41 C1 Left Ctrl 1D 9D F5 3F BF Left Shift 2A AA F6 40 C0 Num Lock 45 C5 F8 42 C2 Right Shift 36 B6 F9 43 C3 Scroll Lock 46 C6 F10 44 C4 Space 39 B9 F11 57 D7 Sys Req (AT) 54 D4 F12 58 D8 Tab 0F 8F % Keypad Keys Make Break Keypad 0 (Ins) 52 D2 Keypad 1 (End) 4F CF Keypad 2 (Down arrow) 50 D0 Keypad 3 (PgDn) 51 D1 Keypad 4 (Left arrow) 4B CB Keypad 5 4C CC Keypad 6 (Right arrow) 4D CD Keypad 7 (Home) 47 C7 Keypad 8 (Up arrow) 48 C8 Keypad 9 (PgUp) 49 C9 Keypad . (Del) 53 D3 Keypad * (PrtSc) 37 B7 Keypad - 4A CA Keypad + 4E CE % Key Make Break Key Make Break A 1E 9E N 31 B1 B 30 B0 O 18 98 C 2E AE P 19 99 D 20 A0 Q 10 90 E 12 92 R 13 93 F 21 A1 S 1F 9F G 22 A2 T 14 94 H 23 A3 U 16 96 I 17 97 V 2F AF J 24 A4 W 11 91 K 25 A5 X 2D AD L 26 A6 Y 15 95 M 32 B2 Z 2C AC % Key Make Break Key Make Break 1 02 82 - 0C 8C 2 03 83 = 0D 8D 3 04 84 [ 1A 9A 4 05 85 ] 1B 9B 5 06 86 ; 27 A7 6 07 87 ' 28 A8 7 08 88 ` 29 A9 8 09 89 \ 2B AB 9 0A 8A , 33 B3 0 0B 8B . 34 B4 / 35 B5 ^Enhanced Keyboard Keys (101/102 keys) % Control Keys Make Break Alt-PrtSc (SysReq) 54 D4 Ctrl-PrtSc E0 37 E0 B7 Enter E0 1C E0 9C PrtSc E0 2A E0 37 E0 B7 E0 AA Right Alt E0 38 E0 B8 Right Ctrl E0 1D E0 9D Shift-PrtSc E0 37 E0 B7 / E0 35 E0 B5 Pause E1 1D 45 E1 9D C5 (not typematic) Ctrl-Pause (Ctrl-Break) E0 46 E0 C6 (not typematic) - Keys marked as "not typematic" generate one stream of bytes without corresponding break scan code bytes (actually the break codes are part of the make code). % Normal Mode or % Shift w/Numlock % Key Make Break ÚÄÄÄÄÄ Numlock on ÄÄÄÄÄÄ¿ % Make Break Del E0 53 E0 D3 E0 2A E0 53 E0 D3 E0 AA Down arrow E0 50 E0 D0 E0 2A E0 50 E0 D0 E0 AA End E0 4F E0 CF E0 2A E0 4F E0 CF E0 AA Home E0 47 E0 C7 E0 2A E0 47 E0 C7 E0 AA Ins E0 52 E0 D2 E0 2A E0 52 E0 D2 E0 AA Left arrow E0 4B E0 CB E0 2A E0 4B E0 CB E0 AA PgDn E0 51 E0 D1 E0 2A E0 51 E0 D1 E0 AA PgUp E0 49 E0 C9 E0 2A E0 49 E0 C9 E0 AA Right arrow E0 4D E0 CD E0 2A E0 4D E0 CD E0 AA Up arrow E0 48 E0 C8 E0 2A E0 48 E0 C8 E0 AA % Key ÚÄÄLeft Shift PressedÄÄ¿ ÚÄÄRight Shift PressedÄÄ¿ % Make Break Make Break Del E0 AA E0 53 E0 D3 E0 2A E0 B6 E0 53 E0 D3 E0 36 Down arrow E0 AA E0 50 E0 D0 E0 2A E0 B6 E0 50 E0 D0 E0 36 End E0 AA E0 4F E0 CF E0 2A E0 B6 E0 4F E0 CF E0 36 Home E0 AA E0 47 E0 C7 E0 2A E0 B6 E0 47 E0 C7 E0 36 Ins E0 AA E0 52 E0 D2 E0 2A E0 B6 E0 52 E0 D2 E0 36 Left arrow E0 AA E0 4B E0 CB E0 2A E0 B6 E0 4B E0 CB E0 36 PgDn E0 AA E0 51 E0 D1 E0 2A E0 B6 E0 51 E0 D1 E0 36 PgUp E0 AA E0 49 E0 C9 E0 2A E0 B6 E0 49 E0 C9 E0 36 Right arrow E0 AA E0 4D E0 CD E0 2A E0 B6 E0 4D E0 CD E0 36 Up arrow E0 AA E0 48 E0 C8 E0 2A E0 B6 E0 48 E0 C8 E0 36 / E0 AA E0 35 E0 B5 E0 2A E0 B6 E0 35 E0 B5 E0 36 - The PS/2 models have three make/break scan code sets. The first set matches the PC & XT make/break scan code set and is the one listed here. Scan code sets are selected by writing the value F0 to the keyboard via the ~8042~ (port 60h). The following is a brief description of the scan code sets (see the PS/2 Technical Reference manuals for more information on scan code sets 2 and 3): ù set 1, each key has a base scan code. Some keys generate extra scan codes to generate artificial shift states. This is similar to the standard scan code set used on the PC and XT. ù set 2, each key sends one make scan code and two break scan codes bytes (F0 followed by the make code). This scan code set is available on the IBM AT also. ù set 3, each key sends one make scan code and two break scan codes bytes (F0 followed by the make code) and no keys are altered by Shift/Alt/Ctrl keys. ù typematic scan codes are the same as the make scan code - Some Tandy 1000's do not handle Alt key combinations when multiple shift keys are pressed. The Alt-Shift-H combination loses the Alt. - extended keys like (F11, F12) can only be read with systems that have extended keyboard BIOS support (or ~INT 9~ extensions); to read these special keys on these systems ~INT 16,10~ must be used - see ~SCAN CODES~ ~KB FLAGS~ ~KEYBOARD COMMANDS~ :GDT:Global Descriptor Table ^GDT - Global Descriptor Table % Offset Size Description 00 8bytes dummy, set to 0 08 8bytes ~GDT~ data segment location, set to 0 10 8bytes source GDT pointer 18 8bytes target GDT pointer 20 8bytes pointer to BIOS code segment, set to 0. used by the BIOS to create protected mode code segment 28 8bytes pointer to BIOS stack segment, set to 0. Used by the BIOS to create protected mode stack segment 30 8bytes user code segment 38 8bytes temporary BIOS code segment % Source/Target GDT use the following format (offsets 10h and 18h): % Offset Size Description 00 word Segment limit 02 3bytes 24 bit segment physical address 05 byte data access rights, set to 93h 06 word reserved word, must be 0 - see ~LGDT~ ~SGDT~ :media descriptor byte ^Media Descriptor Byte % Media Descriptor Byte Layout: ³7³6³5³4³3³2³1³0³ IBM Media Descriptor Byte ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1 = 2 sided, 0 = not 2 sided ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 1 = 8 sector, 0 = not 8 sector ³ ³ ³ ³ ³ ÀÄÄÄÄÄ 1 = removable, 0 = not removable ÀÄÁÄÁÄÁÄÁÄÄÄÄÄÄ must be set to 1 F8 Hard disk Double sided 18 sector diskette PS/2 1.44 Mb. DSQD F9 5¬ Double sided, High Density diskette (15 sector) 3« Double Sided, Double High Density diskette (9 sector) FA Ram disk (not all Ramdisks use this) FC 5¬ Single Sided, Double Density diskette (9 sector) 8 inch Double Sided, Single Density diskette FD 5¬ Double Sided, Double Density (9 sector) 8 inch Double Sided Single Density (26 sector) (IBM 3740 format) 128 bytes per sector, soft sector, 4 sectors cluster, 4 reserved sectors, 2 FATs, 68 directory entries, 77*26*2 sectors. FE 5¬ Single Sided, Double Density diskette (8 sector) 8 inch Single Sided, Single Density diskette (26 sector) (IBM 3740 format) 128 bytes per sector, soft sector, 4 sectors per cluster, 1 reserved sector, 2 FATs. 68 directory entries, 77*26 sectors. 8 inch Double Sided, Double Density (8 sector), 1024 bytes per sector, soft sector, 1 sector per cluster, 1 reserved sector, 2 FATs, 192 directory entries, 77*8*2 sectors. To distinguish from 8 inch SS/SD attempt read of side 2. FF 5¬ Double Sided, Double Density diskette (8 sector) - see also ~INT 21,1B~ ~INT 21,1C~ ~FAT~ :Memory Control Block:MCB ^MCB - DOS Memory Control Block Format % Offset Size Description 00 byte 'M' 4Dh member of a MCB chain, (not last) 'Z' 5Ah indicates last entry in MCB chain other values cause "Memory Allocation Failure" on exit 01 word ~PSP~ segment address of MCB owner (Process Id) possible values: 0 = free 8 = Allocated by DOS before first user pgm loaded other = Process Id/PSP segment address of owner 03 word number of paras related to this MCB (excluding MCB) 05 11bytes reserved 08 8bytes ASCII program name, NULL terminated if less than max length (DOS 4.x+) 10 nbytes first byte of actual allocated memory block - to find the first MCB in the chain, use ~INT 21,52~ - DOS 3.1+ the first memory block contains the DOS data segment ie., installable drivers, buffers, etc - DOS 4.x the first memory block is divided into subsegments, with their own memory control blocks; offset 0000h is the first - the 'M' and 'Z' are said to represent Mark Zbikowski - the MCB chain is often referred to as a linked list, but technically isn't ^DOS 4.x Initial Data Segment Subsegment Control Blocks: % Offset Size Description 00 byte subsegment type 'D' device driver 'E' device driver appendage 'I' Installable File System driver 'F' FILES= control block storage area (for FILES>5) 'X' FCBS= control block storage area, if present 'C' BUFFERS EMS workspace area if BUFFERS /X is used 'B' BUFFERS= storage area 'L' LASTDRIVE= current directory structure array 'S' STACKS= code/data area, if present (see below) 01 word paragraph of subsegment start 03 word subsegment size in paragraphs 05 3bytes unused 08 types "D" and "I", filename of driver loaded driver - see ~INT 21,48~ ~INT 21,49~ ~INT 21,4A~ :Program Segment Prefix:PSP ^PSP - DOS Program Segment Prefix Layout % Offset Size Description 00 word machine code ~INT 20~ instruction (CDh 20h) 02 word top of memory in segment (paragraph) form 04 byte reserved for DOS, usually 0 05 5bytes machine code instruction long call to the DOS function dispatcher (obsolete CP/M) 06 word .COM programs bytes available in segment (CP/M) 0A dword ~INT 22~ terminate address; DOS loader jumps to this address upon exit; the EXEC function forces a child process to return to the parent by setting this vector to code within the parent (IP,CS) 0E dword ~INT 23~ Ctrl-Break exit address; the original INT 23 vector is NOT restored from this pointer (IP,CS) 12 dword ~INT 24~ critical error exit address; the original INT 24 vector is NOT restored from this field (IP,CS) 16 word parent process segment addr (Undoc. DOS 2.x+) COMMAND.COM has a parent id of zero, or its own PSP 18 20bytes file handle array (Undocumented DOS 2.x+); if handle array element is FF then handle is available. Network redirectors often indicate remotes files by setting these to values between 80-FE. 2C word segment address of the environment, or zero (DOS 2.x+) 2E dword SS:SP on entry to last INT 21 function (Undoc. 2.x+) Ø 32 word handle array size (Undocumented DOS 3.x+) 34 dword handle array pointer (Undocumented DOS 3.x+) 38 dword pointer to previous PSP (deflt FFFF:FFFF, Undoc 3.x+) Ø 3C 20bytes unused in DOS before 4.01 Ø 50 3bytes DOS function dispatcher CDh 21h CBh (Undoc. 3.x+) Ø 53 9bytes unused 5C 36bytes default unopened ~FCB~ #1 (parts overlayed by FCB #2) 6C 20bytes default unopened FCB #2 (overlays part of FCB #1) 80 byte count of characters in command tail; all bytes following command name; also default ~DTA~ (128 bytes) 81 127bytes all characters entered after the program name followed by a CR byte - offset 5 contains a jump address which is 2 bytes too low for PSP's created by the DOS EXEC function in DOS 2.x+ Ø - program name and complete path can be found after the environment in DOS versions after 3.0. See offset 2Ch. Ø see ~Bibliography~ for reference to "Undocumented DOS" :scan codes ^INT 16 - Keyboard Scan Codes % Key Normal Shifted w/Ctrl w/Alt A 1E61 1E41 1E01 1E00 B 3062 3042 3002 3000 C 2E63 2E42 2E03 2E00 D 2064 2044 2004 2000 E 1265 1245 1205 1200 F 2166 2146 2106 2100 G 2267 2247 2207 2200 H 2368 2348 2308 2300 I 1769 1749 1709 1700 J 246A 244A 240A 2400 K 256B 254B 250B 2500 L 266C 264C 260C 2600 M 326D 324D 320D 3200 N 316E 314E 310E 3100 O 186F 184F 180F 1800 P 1970 1950 1910 1900 Q 1071 1051 1011 1000 R 1372 1352 1312 1300 S 1F73 1F53 1F13 1F00 T 1474 1454 1414 1400 U 1675 1655 1615 1600 V 2F76 2F56 2F16 2F00 W 1177 1157 1117 1100 X 2D78 2D58 2D18 2D00 Y 1579 1559 1519 1500 Z 2C7A 2C5A 2C1A 2C00 % Key Normal Shifted w/Ctrl w/Alt 1 0231 0221 7800 2 0332 0340 0300 7900 3 0433 0423 7A00 4 0534 0524 7B00 5 0635 0625 7C00 6 0736 075E 071E 7D00 7 0837 0826 7E00 8 0938 092A 7F00 9 0A39 0A28 8000 0 0B30 0B29 8100 % Key Normal Shifted w/Ctrl w/Alt - 0C2D 0C5F 0C1F 8200 = 0D3D 0D2B 8300 [ 1A5B 1A7B 1A1B 1A00 ] 1B5D 1B7D 1B1D 1B00 ; 273B 273A 2700 ' 2827 2822 ` 2960 297E \ 2B5C 2B7C 2B1C 2600 (same as Alt L) , 332C 333C . 342E 343E / 352F 353F % Key Normal Shifted w/Ctrl w/Alt F1 3B00 5400 5E00 6800 F2 3C00 5500 5F00 6900 F3 3D00 5600 6000 6A00 F4 3E00 5700 6100 6B00 F5 3F00 5800 6200 6C00 F6 4000 5900 6300 6D00 F7 4100 5A00 6400 6E00 F8 4200 5B00 6500 6F00 F9 4300 5C00 6600 7000 F10 4400 5D00 6700 7100 F11 8500 8700 8900 8B00 F12 8600 8800 8A00 8C00 % Key Normal Shifted w/Ctrl w/Alt BackSpace 0E08 0E08 0E7F 0E00 Del 5300 532E 9300 A300 Down Arrow 5000 5032 9100 A000 End 4F00 4F31 7500 9F00 Enter 1C0D 1C0D 1C0A A600 Esc 011B 011B 011B 0100 Home 4700 4737 7700 9700 Ins 5200 5230 9200 A200 Keypad 5 4C35 8F00 Keypad * 372A 9600 3700 Keypad - 4A2D 4A2D 8E00 4A00 Keypad + 4E2B 4E2B 4E00 Keypad / 352F 352F 9500 A400 Left Arrow 4B00 4B34 7300 9B00 PgDn 5100 5133 7600 A100 PgUp 4900 4939 8400 9900 PrtSc 7200 Right Arrow 4D00 4D36 7400 9D00 SpaceBar 3920 3920 3920 3920 Tab 0F09 0F00 9400 A500 Up Arrow 4800 4838 8D00 9800 - Some key combinations are not available on all systems. The PS/2 includes many that aren't available on the PC, XT and AT. - To retrieve the character from a scan code logical AND the word with 0x00FF. - see ~INT 16~ ~MAKE CODES~ :SFT:file table:System File Table ^System File Table (Undocumented) ^DOS 2.x System File Table Format % Offset Size Description 00 dword pointer to next system file table; offset of ffffh indicates last table in chain 04 word number of file descriptors in table 06 nbytes file descriptor table of the format (40 bytes each): % Offset Size Description 00 byte count of handles referring to this file or zero if file is no longer open 01 byte open mode 02 byte file attribute 03 byte drive (1=A, 2=B:, ..., 0=char device) 04 11bytes filename in ~FCB~ format 0F word unknown 11 word unknown 13 dword file size 17 word file date 19 word file time 1B byte device attribute 1C word starting cluster of file (block device) dword pointer to device driver (if char device) 1E word if block device, relative cluster within file of the last cluster read; zero if file has never been read or written 20 word absolute cluster number of current cluster 22 word unknown 24 dword current file position ^DOS 3.x System File Table and FCB Table Format % Offset Size Description 00 dword pointer to next system file table; offset of ffffh indicates last table in chain 04 word number of file descriptors in table 06 nbytes file descriptor table of the format (53 bytes each): % Offset Size Description 00 word count of handles referring to this file or zero if file is no longer open 02 word open mode, bit 15 set if file id opened via FCB 04 byte file attribute 05 word device info word 07 dword if char device pointer to device driver header if block device pointer to DOS Device Control Block 0B word starting cluster of file 0D word file time 0F word file date 11 dword file size 15 dword current file position 19 word if block device, relative cluster within file of the last cluster read 1B word absolute cluster number of last cluster read zero if file has never been read or written 1D word sector number containing the directory entry 1F byte number of dir entry within sector 20 11bytes filename in ~FCB~ format 2B dword SHARE pointer to previous ~SFT~ sharing same file 2F word SHARE number of network machine opening file 31 word PSP segment of file owner 33 word offset within SHARE code segment of sharing record 0000h = none ^DOS 4.0+ System File Table and FCB Table % Offset Size Description 00 dword pointer to next system file table; offset of ffffh indicates last table in chain 04 word number of file descriptors in table 06 nbytes file descriptor table of the format (59 bytes each): % Offset Size Description 00 word count of handles referring to this file or zero if file is no longer open 02 word open mode, bit 15 set if file id opened via FCB 04 byte file attribute 05 word device info word 07 dword if char device pointer to device driver header if block device pointer to DOS Device Control Block or REDIR data 0B word starting cluster of file 0D word file time 0F word file date 11 dword file size 15 dword current file position 19 dword if network redirector, pointer to REDIRIFS record word if local block dev, relative cluster within file of the last cluster read 1B dword if local, sector number of directory entry 1F byte if local, number of directory entry within sector 20 11bytes filename in ~FCB~ format 2B dword SHARE pointer to previous ~SFT~ sharing same file 2F word SHARE number of network machine opening file 31 word PSP segment of file owner 33 word offset within SHARE code seg of sharing record 0000h = none 35 word absolute cluster number of last cluster read zero if file has never been read or written 37 dword pointer to file IFS driver, NULL if native DOS - these structures are allocated by DOS during the scanning of the CONFIG.SYS file - ~INT 21,67~ can be used to allow an application to have more than 20 file handles; the total number of handles is limited still to the value of FILES=n in CONFIG.SYS - the structure of these fields is undocumented; I do not recommend relying on any of this information, instead use it as an aid in debugging - see ~Bibliography~ references to Bernd Schemmer and "Data Structures Used in IBM PC Compatibles and the PS/2". - see ~INT 21,52~ :system descriptor ^BIOS System Descriptor Table (PS/2) % Offset Size Description 00 word length of descriptor (8 minimum) 02 byte model byte (same as FFFF:E, not reliable) 03 byte secondary model byte 04 byte BIOS revision level (zero based) 05 byte feature information (see table) 06 dword reserved ³7³6³5³4³3³2³1³0³ feature information at offset 5 ³ ³ ³ ³ ³ ³ ³ ÀÄÄÄ reserved ³ ³ ³ ³ ³ ³ ÀÄÄÄÄ 0=PC bus, 1=Micro Channel ³ ³ ³ ³ ³ ÀÄÄÄÄÄ Extended BIOS Data Area (~EBDA~) allocated ³ ³ ³ ³ ÀÄÄÄÄÄÄ wait for external event supported ³ ³ ³ ÀÄÄÄÄÄÄÄ ~INT 15,4F~ used (kbd intercept) ³ ³ ÀÄÄÄÄÄÄÄÄ RTC present ³ ÀÄÄÄÄÄÄÄÄÄ 2nd ~8259~ present ÀÄÄÄÄÄÄÄÄÄÄ DMA channel 3 used by fixed disk BIOS - see also ~MACHINE IDENT~ and ~INT 15,C0~ :video information:video tables ^Video Information Tables % BIOS Data Area Fields % Address Size Description 40:49 byte Current video mode (see ~VIDEO MODE~) 40:4A word Number of screen columns 40:4C word Size of video regen buffer in bytes 40:4E word Starting address in video regen buffer (offset) 40:50 8 words Cursor position of pages 1-8, high order byte=row, low order byte=column 40:60 byte Ending (bottom) scan line for cursor 40:61 byte Starting (top) scan line for cursor 40:62 byte Active display page number 40:63 word Base port address for active ~6845~ CRT controller 3B4h = mono, 3D4h = color 40:65 byte 6845 CRT mode control register value (port 3x8h) EGA/VGA values emulate those of the MDA/CGA 40:66 byte CGA current color palette setting (port 3d9h) EGA and VGA values emulate the CGA 40:84 byte Rows on the screen (less 1, EGA+) 40:85 word Point height of character matrix (EGA+) 40:87 byte Video mode options (EGA+) ³7³6³5³4³3³2³1³0³ Video mode options (EGA+) ³ ³ ³ ³ ³ ³ ³ ÀÄÄ 1=alphanumeric cursor emulation enabled ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1=video subsystem attached to monochrome ³ ³ ³ ³ ³ ÀÄÄÄÄ reserved ³ ³ ³ ³ ÀÄÄÄÄÄ 1=video subsystem is inactive ³ ³ ³ ÀÄÄÄÄÄÄ reserved ³ ÀÄÁÄÄÄÄÄÄÄ video RAM 00-64K 10-192K 01-128K 11-256K ÀÄÄÄÄÄÄÄÄÄÄ video mode number passed to ~INT 10~, function 0 40:88 byte EGA feature bit switches, emulated on VGA ³7³6³5³4³3³2³1³0³ EGA feature bit switches (EGA+) ³ ³ ³ ³ ³ ³ ³ ÀÄÄ EGA SW1 config (1=off) ³ ³ ³ ³ ³ ³ ÀÄÄÄ EGA SW2 config (1=off) ³ ³ ³ ³ ³ ÀÄÄÄÄ EGA SW3 config (1=off) ³ ³ ³ ³ ÀÄÄÄÄÄ EGA SW4 config (1=off) ³ ³ ³ ÀÄÄÄÄÄÄ Input FEAT0 (ISR0 bit 5) after output on FCR0 ³ ³ ÀÄÄÄÄÄÄÄ Input FEAT0 (ISR0 bit 6) after output on FCR0 ³ ÀÄÄÄÄÄÄÄÄ Input FEAT1 (ISR0 bit 5) after output on FCR1 ÀÄÄÄÄÄÄÄÄÄ Input FEAT1 (ISR0 bit 6) after output on FCR1 40:89 byte Video display data area (MCGA and VGA) ³7³6³5³4³3³2³1³0³ Video display data area (MCGA and VGA) ³ ³ ³ ³ ³ ³ ³ ÀÄÄ 1=VGA is active ³ ³ ³ ³ ³ ³ ÀÄÄÄ 1=gray scale is enabled ³ ³ ³ ³ ³ ÀÄÄÄÄ 1=using monochrome monitor ³ ³ ³ ³ ÀÄÄÄÄÄ 1=default palette loading is disabled ³ ³ ³ ÀÄÄÄÄÄÄ see table below ³ ³ ÀÄÄÄÄÄÄÄ reserved ³ ÀÄÄÄÄÄÄÄÄ 1=display switching enabled ÀÄÄÄÄÄÄÄÄÄ alphanumeric scan lines (see table below) % Bit7 Bit4 Scan Line information 0 0 350 line mode 0 1 400 line mode 1 0 200 line mode 1 1 reserved 40:8A byte Display Combination Code (DCC) table index (EGA+) 40:A8 dword BIOS Video Save/Override Pointer Table address ^EGA / VGA Related Tables % Video Save/Override Pointer Table (pointer at 40:A8): 00 dword Video Parameter Table pointer 04 dword Dynamic Parameter Save Area pointer (EGA, VGA) 08 dword Alphanumeric Character Set Override pointer 0C dword Graphics Character Set Override pointer 10 dword Secondary Save Pointer Table pointer (VGA) 14 dword reserved, set to 0000:0000 18 dword reserved, set to 0000:0000 % Video Parameter Table 00 byte number of displayed character columns 01 byte number of displayed screen rows minus 1 02 byte character matrix height in points 03 word video buffer size in bytes 05 dword contents of sequencer registers 1-4 09 byte misc. output register values 0A 25bytes contents of CRTC registers 0-18h 23 20bytes contents of attribute controller regs 0-13h 37 9 bytes contents of graphics controller regs 0-8 % Dynamic Parameter Save Area 00 16bytes contents of graphics controller pallette regs 10 byte contents of graphics controller overscan reg 11 239bytes reserved % Alphanumeric Character Set Override 00 byte length of each character definition in bytes 01 byte character generator RAM bank 02 word count of characters defined 04 word first character code in table 06 dword pointer to character font definition table 0A byte number of character rows displayed 0B nbytes array of applicable video modes 0B+n byte FFh end of mode list marker % Graphics Character Set Override 00 byte count of displayed character rows 01 word length of each character definition in bytes 03 dword pointer to character font definition table 07 nbytes array of applicable video modes 07+n byte FFh end of mode list marker % Secondary Save Pointer Table 00 word length of table in bytes 02 dword pointer to display combination code table 06 dword pointer to secondary alphanumeric char set override 0A dword pointer to user palette profile table (VGA) 0E dword reserved 12 dword reserved 16 dword reserved % Display Combination Code Table 00 byte number of table entries 01 byte DCC table version number 02 byte maximum display type code 03 byte reserved 04 n words array valid display combinations: 0,0 entry 0 no display 0,1 entry 1 MDPA 0,2 entry 2 CGA 2,1 entry 3 MDPA + CGA 0,4 entry 4 EGA 4,1 entry 5 EGA + MDPA 0,5 entry 6 MEGA 2,5 entry 7 MEGA + CGA 0,6 entry 8 PGC 1,6 entry 9 PGC + MDPA 5,6 entry 10 PGC + MEGA 0,8 entry 11 CVGA 1,8 entry 12 CVGA + MDPA 0,7 entry 13 MVGA 2,7 entry 14 MVGA + CGA 2,6 entry 15 MVGA + PGC % Secondary Alpha Mode Auxillary Character Generator Table 00 byte bytes per character 01 byte block to load 02 byte reserved 03 dword font table pointer 07 nbytes array of mode values for this font 07+n byte FFh end of mode list marker % Palette Profile Table (VGA only) 00 byte 1 - enable underlining in all alphanumeric modes 0 - enable underlining in monochrome alpha modes -1 - disable underlining in all alpha modes 01 byte reserved 02 word reserved 04 word count of attribute controller regs in table 06 word first attribute controller register number 08 dword pointer to attribute controller reg table 0C word count of video DAC color registers in table 0E word first video DAC color register number 10 dword video DAC color register table pointer 14 nbytes array of applicable video modes for this font 14+n byte FFh end of video mode list marker - see also ~BIOS Data Area~ - see ~INT 10,1B~ for Dynamic Video State Table and Video Static Functionality Table :video pages ^Video modes and corresponding number of pages % Mode Pages Adapters 00 pages 0-7 (CGA,EGA,MCGA,VGA) 01 pages 0-7 (CGA,EGA,MCGA,VGA) 02 pages 0-3 (CGA) pages 0-7 (EGA,MCGA,VGA) 03 pages 0-3 (CGA) pages 0-7 (EGA,MCGA,VGA) 07 pages 0-7 (EGA,VGA) no pages (MDA) 0D pages 0-7 (EGA,VGA) 0E pages 0-4 (EGA,VGA) 0F pages 0-1 (EGA,VGA) 10 pages 0-1 (EGA,VGA) :XFCB:Extended FCB:extended file ctlblk ^XFCB - Extended DOS File Control Block % Offset Size Description 00 byte flag containing FF if this is an extended ~FCB~ 01 5bytes reserved 06 byte directory attribute byte (see ~FILE ATTRIBUTE~) 07 byte drive number (0 for default drive, 1 = A:, 2 = B:) 08 8bytes filename, left justified with trailing blanks 16 3bytes filename extension, left justified w/blanks 19 word current block number relative to file start (0 based) 21 word logical record size in bytes 23 dword file size in bytes 27 word date the file was created or last updated: ³F³E³D³C³B³A³9³8³7³6³5³4³3³2³1³0³ 21,20 ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÁÄ day 1-31 ³ ³ ³ ³ ³ ³ ³ ÀÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄ month 1-12 ÀÄÁÄÁÄÁÄÁÄÁÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ year + 1980 29 16bytes reserved for system use 39 byte relative record number within current BLOCK 40 4bytes relative record number from start of file (0 based)