: Help ! I'm desperate ! I need to find out the address in BIOS where is stored the value for boot drive. I'm not talkin here about the logical boot drive (like A:, C:, D: ...etc) but i'm talking about the physical boot drive (0 for floppy, 80h for first harddisk, 81h for the second harddisk ... etc). Any system call wouldnt help me because i want to be operating system indpendent except that if that system call can tell me the address where i can find the value for the boot physical drive.
: Anyone can help me ?!
:
The Drive type is located in CMOS RAM and the addresses are as follows:
10 Diskette drive types
== ====================
bits 7-4 - drive 0 type (A:)
bits 3-0 - drive 1 type (B:)
0000b - no drive
0001b - 360k
0010b - 1.2M
0011b - 720k
0100b - 1.44M
11 Reserved
12 Hard disk drive type
== ====================
(for drives C: and D:, when between 1 and 14)
bits 7-4 - fixed disk 0 type (C:)
bits 3-0 - fixed disk 1 type (D:)
0000b = no drive
0001b-1110b = drive type
1111b = drive 0 (1) type stored at addr 19h (1Ah)
13 Reserved
14 Equipment byte
== ==============
bits 7-6 - no. of floppy drives (00=1, 01=2, 10=3, 11=4)
bits 5-4 - primary display 00 = none, EGA, VGA ...
01 = 40x25 colour
10 = 80x25 colour
11 = 80x25 monochrome
bits 3-2 - reserved
bit 1 =1 if math copro installed
bit 0 =1 if floppy drive(s) present
19 Disk 0 type if (CMOS addr 12H & 0fH) is 0fH
1A Disk 1 type if (CMOS addr 12H & f0H) is f0H
what you have to do is-
;Read a cmos register
cli ; make sure no interrupt wants to access the RTC in the mean time
mov al,10h
out 70h,al ;first let himknow which address you want to read/write to
nop ;a slight delay
in al,71h ;then read
sti
cli
mov al,12h ;same as above.
out 70h,al
nop
in al,71h
sti
