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Subject: Re: ATA 4 KiB sector issues.
From: James Bottomley <James.Bottomley@suse.de>
To: Tejun Heo <tj@kernel.org>
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Date: Tue, 16 Mar 2010 08:02:28 -0700
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On Tue, 2010-03-16 at 23:50 +0900, Tejun Heo wrote:
> e.g.  If the first partition begins at CHS 0/32/33 and ends at
> 12/233/19 and the corresponding LBA addresses are 2048 and 206848, you
> can solve the equation and determine that the parameters gotta be 63
> secs/trk and 255 heads/cyl to make those two pairs of addresses match
> each other and in fact some BIOSs try to do this depending on
> configuration (and sometimes falls into infinite loop or causes other
> boot related problems if the parameters are too uncommon).

for an msdos label, this is illegal, that was Arnd's point.  The
partitions have to begin and end on cylinder boundaries*.  Knowing that,
you can deduce the geometry from the last sector entry.

James

* at least if you want to preserve windows compatibility, which is what
most of our partitioning tools seem to do.