Legend:
S - set by the emulator (Bochs)
Q - set by the emulator (Qemu)
B - set by the bios
U - unused by the bios
LOC NOTES MEANING
0x00 S rtc seconds
0x01 B second alarm
0x02 S rtc minutes
0x03 B minute alarm
0x04 S rtc hours
0x05 B hour alarm
0x06 S,U day of week
0x07 S,B date of month
0x08 S,B month
0x09 S,B year
0x0a S,B status register A
0x0b S,B status register B
0x0c S status register C
0x0d S status register D
0x0f S shutdown status
values:
0x00: normal startup
0x09: normal
0x0d+: normal
0x05: eoi ?
else: unimpl
0x10 S fd drive type (2 nibbles: high=fd0, low=fd1)
values:
1: 360K 5.25"
2: 1.2MB 5.25"
3: 720K 3.5"
4: 1.44MB 3.5"
5: 2.88MB 3.5"
!0x11 configuration bits!!
0x12 S how many disks first (hd type)
!0x13 advanced configuration bits!!
0x14 S,U equipment byte (?)
bits where what
7-6 floppy.cc
5-4 vga.cc 0 = vga
2 keyboard.cc 1 = enabled
0 floppy.cc
0x15 S,U base memory - low
0x16 S,U base memory - high
0x17 S,U extended memory in k - low
0x18 S,U extended memory in k - high
0x19 S hd0: extended type
0x1a S hd1: extended type
0x1b S,U hd0:cylinders - low
0x1c S,U hd0:cylinders - high
0x1d S,U hd0:heads
0x1e S,U hd0:write pre-comp - low
0x1f S,U hd0:write pre-comp - high
0x20 S,U hd0:retries/bad_map/heads>8
0x21 S,U hd0:landing zone - low
0x22 S,U hd0:landing zone - high
0x23 S,U hd0:sectors per track
0x24 S,U hd1:cylinders - low
0x25 S,U hd1:cylinders - high
0x26 S,U hd1:heads
0x27 S,U hd1:write pre-comp - low
0x28 S,U hd1:write pre-comp - high
0x29 S,U hd1:retries/bad_map/heads>8
0x2a S,U hd1:landing zone - low
0x2b S,U hd1:landing zone - high
0x2c S,U hd1:sectors per track
0x2d S boot from (bit5: 0:hd, 1:fd)
0x2e S,U standard cmos checksum (0x10->0x2d) - high
0x2f S,U standard cmos checksum (0x10->0x2d) - low
0x30 S extended memory in k - low
0x31 S extended memory in k - high
0x32 S rtc century
0x34 S extended memory in 64k - low
0x35 S extended memory in 64k - high
0x37 S ps/2 rtc century (copy of 0x32, needed for winxp)
0x38 S eltorito boot sequence + boot signature check
bits
0 floppy boot signature check (1: disabled, 0: enabled)
7-4 boot drive #3 (0: unused, 1: fd, 2: hd, 3:cd, else: fd)
0x39 S ata translation policy - ata0 + ata1
bits
1-0 ata0-master (0: none, 1: LBA, 2: LARGE, 3: R-ECHS)
3-2 ata0-slave
5-4 ata1-master
7-6 ata1-slave
0x3a S ata translation policy - ata2 + ata3 (see above)
0x3d S eltorito boot sequence (see above)
bits
3-0 boot drive #1
7-4 boot drive #2
0x5b S extra memory above 4GB
0x5c S extra memory above 4GB
0x5d S extra memory above 4GB
0x5f Q number of processors |