bios_data_area

anonymous@undisclosed.example.com (Anonymous) — Tue, 13 Aug 2024 09:23:55 +0000

BDA - BIOS Data Area - PC Memory Map - WIP 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

cmos_ram

anonymous@undisclosed.example.com (Anonymous) — Sun, 22 Dec 2024 10:50:17 +0000

CMOS RTC - Real Time Clock and Memory (ports 70h & 71h) The information here is only applicable to AT and PS/2 systems Reg# Description 00 RTC seconds

disk_base_table

anonymous@undisclosed.example.com (Anonymous) — Thu, 19 Jan 2023 21:04:45 +0000

DBT - Disk Base Table (BIOS INT 13) Offset Size Description 00 byte specify byte 1; step-rate time, head unload time

dos_error_code

anonymous@undisclosed.example.com (Anonymous) — Mon, 16 Jan 2023 16:54:33 +0000

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 0x21,0x59 Extended DOS Error Code 00 No Error

edba

anonymous@undisclosed.example.com (Anonymous) — Mon, 16 Jan 2023 17:03:36 +0000

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

executable-header-format

anonymous@undisclosed.example.com (Anonymous) — Mon, 16 Jan 2023 16:54:33 +0000

Executable Header Format Format of .EXE file header: Offset Size Description 00h 2 BYTEs .EXE signature, either

file_control_block

anonymous@undisclosed.example.com (Anonymous) — Mon, 16 Jan 2023 16:54:33 +0000

FCB - DOS File Control Block Standard DOS File Control Block Offset Size Description 00 byte drive number (0 for default drive, 1=A:, 2=B:,

file-system-format

anonymous@undisclosed.example.com (Anonymous) — Fri, 03 Mar 2023 16:52:54 +0000

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

irq

anonymous@undisclosed.example.com (Anonymous) — Mon, 12 Jan 2026 08:09:58 +0000

IRQs - Interrupts List Intel Defined CPU Exception Table (see notes) Interrupt Function 0 Divide by zero 1 Single step 2 Non-maskable (NMI)

kb_flags

anonymous@undisclosed.example.com (Anonymous) — Sun, 07 Apr 2024 01:00:33 +0000

Keyboard Memory Bytes Keyboard Flags Bytes 0 and 1 bit 40:17 Keyboard Flags Byte 0 0 right shift key depressed 1 left shift key depressed 2 CTRL key depressed 3 ALT key depressed 4 scroll-lock is active

keyboard-make-code

anonymous@undisclosed.example.com (Anonymous) — Sun, 11 Jan 2026 22:46:02 +0000

INT 9 - Hardware Keyboard Make/Break Codes Standard Keyboard Key Make Break Backspace 0Eh 8Eh Caps Lock 3Ah BAh Enter 1Ch 9Ch Esc 01h 81h Left Alt 38h

keyboard-scan-code

anonymous@undisclosed.example.com (Anonymous) — Sun, 19 Feb 2023 11:55:28 +0000

INT 16 - Keyboard Scan Codes Those table are the AX register return's value: Key Normal Shifted w/Ctrl w/Alt A 1E61 1E41 1E01 1E00 B 3062 3042 3002 3000 C 2E63 2E42 2E03

machine-id

anonymous@undisclosed.example.com (Anonymous) — Mon, 16 Jan 2023 16:54:33 +0000

Machine Identification Byte Model Sub-Model Machine FF ?? Original IBM PC 4/24/81 ?? IBM PC 10/19/81 ??

program_segment_prefix

anonymous@undisclosed.example.com (Anonymous) — Tue, 13 Aug 2024 09:26:58 +0000

PSP - DOS Program Segment Prefix Layout The Program Segment Prefix (PSP) is a data structure used in DOS systems to store the state of a program. It resembles the Zero Page in the CP/M operating system. The PSP has the following structure: Offset

start

anonymous@undisclosed.example.com (Anonymous) — Mon, 16 Jan 2023 16:59:02 +0000

Informations * BDA - BIOS Data Area - PC Memory Map - WIP * CMOS RTC - Real Time Clock and Memory (ports 70h & 71h) * DBT - Disk Base Table (BIOS INT 13) * DOS error Codes * EBDA - Extended BIOS Data Area EBDA (PS/2) * Executable Header Format * FCB - DOS File Control Block * INT 16 - Keyboard Scan Codes * INT 9 - Hardware Keyboard Make/Break Codes * IRQs - Interrupts List * Keyboard Memory Bytes * Machine Identification Byte * PSP - DOS Program Segment Prefix Layout * System Fil…

video_bios_informations

anonymous@undisclosed.example.com (Anonymous) — Thu, 19 Jan 2023 20:16:00 +0000

Video Information Tables BIOS Data Area Fields Address Size Description 40:49 byte Current video mode (see VIDEO MODE)

Nox-Rhea WiKi - back2root:ibm-pc-ms-dos:hardware:informations

bios_data_area

cmos_ram

disk_base_table

dos_error_code

edba

executable-header-format

file_control_block

file-system-format

irq

kb_flags

keyboard-make-code

keyboard-scan-code

machine-id

program_segment_prefix

start

video_bios_informations