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LBA addressing

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    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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  • Mel Bishop
    started a topic LBA addressing

    LBA addressing

    Does anyone have any examples of int13 LBA addressing? My specific
    problem is the "disk address packet". I've read a lot of material
    concerning this but can't make hide-ner-hare of this. Thanks.


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