LBA addressing

1. Check if LBA i/o is supported

TYPE int48buffer
size AS WORD
flags AS WORD
cylinders AS DWORD
heads AS DWORD
sectorspertrack AS DWORD
totalsectors AS QUAD
bytespersector as WORD
END TYPE

int48buffer.size=1Eh

call int 13h, ah=48h

dl=BIOS drive number
ds:si=segment/offset of buffer

if carry clear, then LBA is supported and the buffer will be
filled in. You can ignore everything except the totalsectors
(which is the total number of sectors on the disk).

In some cases the total sectors returned will reflect the BIOS
address limit rather than the actual size of the disk.

If you want CHS parameters use int 13h, ah=8 to get the correct
cylinder and head counts. The only reason you would need CHS
values would be to calculate LBAs for cylinder boundries.

2. to read the disk

TYPE LBApacket
size AS BYTE
reserved AS BYTE
transfer AS WORD
buffoff AS WORD
buffseg AS WORD
LBA AS QUAD
END TYPE

Fill in the LBApacket buffer and call int 13h, ah=42h

LBApacket.size=1Eh
LBApacket.reserved=0
LBAPacket.transfer=number of sectors to read
buffoff/buffseg are offset & segment of the buffer the sectors
are read to.
LBA is the LBA address of the first sector to read.

dl=BIOS drive number
ds:si = segment/offset of LBApacket buffer.

More details can be found in Ralf Brown's Interrupt List.

Bob

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