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    SubjectRe: [Fwd: Hard disk geometry]
        From clausen@alphalink.com.au Fri Oct 22 02:20:21 1999

    OK, then. If it isn't possible to detect geometry, how does Windows
    determine geometry (even if it's geometry is "wrong"). I need to test
    this more, but Windows needs partitions to begin and end on cylinder
    boundaries, although the rules are a lot stranger than this. (long
    story).

    Well - BIOS-using operating systems have one advantage:
    they need not worry which disk is addressed by BIOS 0x80 or 0x81
    as long as they themselves also use the BIOS to address the disk.

    So all that matters to me is that the geometry on the software side,
    no matter what operating system, needs to be the same.

    Does Windows determine the geometry from the partition table ONLY?

    It can use: (i) the disk, (ii) the BIOS setup, (iii) the partition table.
    In a Linux context ingredient (ii) is unavailable.

    If that's the case, then there's no problem - we can use any geometry we
    like, by writing it to the partition table (because Windows assumes each
    partition ends on the end of a cylinder,

    I consider that a common myth. What are your sources, or experiments?
    I did some experiments four years ago and found this false for DOS.
    This is also false for Windows NT on an Alpha.

    the end head and sector values
    should be the size of cylinders and heads, respectively). But I
    suspect it uses BIOS calls to do I/O - at least on
    some systems, which will screw everything up. Can someone confirm this?

    Yes.

    Andries

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