Specifications

164
5.4 BDA and EBDA Memory Addresses
The BIOS Data Area (BDA) starts at 40:0 and is 257 bytes in length. Byte 40:100 is
byted by INT 0x05.
Table 16 BIOS Data Area
Start
Location
Length
in
bytes
Description Modified by
Legacy BIOS
INT
Using It
Comments
0x00 2 COM 1 base address No 14
0x02 2 COM 2 base address No 14
0x04 2 COM 3 base address No 14
0x06 2 COM 4 base address No 14
0x08 2 LPT 1 base address No 17
0x0A 2 LPT 2 base address No 17
0x0C 2 LPT 3 base address No 17
0x0E 2 EBDA segment No
0x10 2 Installed hardware No 11
0x12 1 Reserved No
0x13 2 Base memory size No 12
0x15 2 Reserved No
0x17 1 Keyboard control 1 Yes 16
0x18 1 Keyboard control 2 Yes 16
0x19 1 Work area for ALT key Yes 16
0x1A 2 Keyboard-buffer Head Yes 16
0x1C 2 Keyboard-buffer Tail Yes 16
0x1E 32 Keyboard Buffer Yes 16
0x3E 1 Floppy recalibrate status Yes 13
0x3F 1 Floppy motor status Yes 13
0x40 1 Floppy motor timeout Yes 13
0x41 1 Floppy operation status Yes 13
0x42 7 Floppy controller status Yes 13
0x49 30 Video info No 10
0x67 4 POST re-entry ptr
0x6B 1 Last Unexpected interrupt Yes
0x6C 4 Timer Counter Yes 1A
0x70 1 Timer Overflow Yes 1A
0x71 1 Break key state Yes 16
0x72 2 Reset Flag Yes
0x74 1 HDD operation status Yes 13