Format of Extended BIOS Data Area (IBM)

Offset  Size    Description     (Table M001)
 00h   BYTE    length of EBDA in kilobytes
 01h 15 BYTEs  reserved
 17h   BYTE    number of entries in POST error log (0-5)
 18h  5 WORDs  POST error log (each word is a POST error number)
 22h   DWORD   Pointing Device Driver entry point
 26h   BYTE    Pointing Device Flags 1 (see #M002)
 27h   BYTE    Pointing Device Flags 2 (see #M003)
 28h  8 BYTEs  Pointing Device Auxiliary Device Data
 30h   DWORD   Vector for INT 07h stored here during 80387 interrupt
 34h   DWORD   Vector for INT 01h stored here during INT 07h emulation
 38h   BYTE    Scratchpad for 80287/80387 interrupt code
 39h   WORD    Timer3: Watchdog timer initial count
 3Bh   BYTE    ??? seen non-zero on Model 30
 3Ch   BYTE    ???
 3Dh 16 BYTEs  Fixed Disk parameter table for drive 0 (for older machines
         which don't directly support the installed drive)
 4Dh 16 BYTEs  Fixed Disk parameter table for drive 1 (for older machines
         which don't directly support the installed drive)
 5Dh-67h   ???
 68h   BYTE    cache control
       bits 7-2 unused (0)
       bit 1: CPU cache failed test
       bit 0: CPU cache disabled
 69h-6Bh   ???
 6Ch   BYTE    Fixed disk: (=FFh on ESDI systems)
           bits 7-4: Channel number 00-0Fh
           bits 3-0: DMA arbitration level 00-0Eh
 6Dh   BYTE    ???
 6Eh   WORD    current typematic setting (see INT 16/AH=03h)
 70h   BYTE    number of attached hard drives
 71h   BYTE    hard disk 16-bit DMA channel
 72h   BYTE    interrupt status for hard disk controller (1Fh on timeout)
 73h   BYTE    hard disk operation flags
       bit 7: controller issued operation-complete INT 76h
       bit 6: controller has been reset
       bits 5-0: unused (0)
 74h   DWORD   old INT 76h vector
 78h   BYTE    hard disk DMA type
       typically 44h for reads and 4Ch for writes
 79h   BYTE    status of last hard disk operation
 7Ah   BYTE    hard disk timeout counter
 7Bh-7Dh
 7Eh  8 WORDs  storage for hard disk controller status
 8Eh-E6h
 E7h   BYTE    floppy drive type
       bit 7: drive(s) present
       bits 6-2: unused (0)
       bit 1: drive 1 is 5.25" instead of 3.5"
       bit 0: drive 0 is 5.25"
 E8h  4 BYTEs  ???
 ECh   BYTE    hard disk parameters flag
       bit 7: parameters loaded into EBDA
       bits 6-0: unused (0)
 EDh   BYTE    ???
 EEh   BYTE    CPU family ID (03h = 386, 04h = 486, etc.) (see INT 15/AH=C9h)
 EFh   BYTE    CPU stepping (see INT 15/AH=C9h)
 F0h 39 BYTEs  ???
117h   WORD    keyboard ID (see INT 16/AH=0Ah)
       (most commonly 41ABh)
119h   BYTE    ???
11Ah   BYTE    non-BIOS INT 18h flag
       bits 7-1: unused (0)
       bit 0: set by BIOS before calling user INT 18h at offset 11Dh
11Bh  2 BYTE   ???
11Dh   DWORD   user INT 18h vector if BIOS has re-hooked INT 18h
121h and up:   ??? seen non-zero on Model 60
3F0h   BYTE    Fixed disk buffer (???)

See Also: #M004
Bitfields for Pointing Device Flags 1:
Bit(s) Description (Table M002)
 7 command in progress
 6 resend byte (FAh) received
 5 acknowledge byte (FEh) received
 4 error byte (FCh) received
 3 unexpected value received
 2-0   index count for auxiliary device data at 28h

See Also: #M001,#M003
Bitfields for Pointing Device Flags 2:
Bit(s) Description (Table M003)
 7 device driver far call flag
 6-3   reserved
 2-0   package size (number of bytes received) - 1

See Also: #M001,#M002