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SubjectRe: Disk geometry from /sys
Hello Mark

On Fri, Apr 18, 2008 at 3:22 PM, Mark Lord <lkml@rtr.ca> wrote:
> That can sound a bit misleading. The complete story, for ATA/SATA drives,
> is that the disk has two geometries: an internal physical one, with a
> fixed number of heads and cylinders, but variable sectors/track
> (which normally varies by cylinder zone).
>
> Software *never* sees or knows about that geometry, so ignore it.
>
> The second geometry, is the one that the drive reports to software
> as its "native" geometry. This is what you see from "hdparm -I"
> and friends, and this geometry is what has to be used by software
> when using cylinder/head/sector (CHS) addressing for I/O operations.
> The hardware interface has a limit of 4-bits for the head value,
> so the maximum number of heads can never be more than 16.
>
> Nobody uses CHS addressing for I/O operations, at least not on
> any hardware newer than at least ten years old, so this geometry
> is also unimportant for most uses.
>

Is it because IDE drives support several IO operation modes ?

thanks
--
Francis


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