Hi Murray,

On 02-Dec-99, Murray Lesser wrote to Will Honea:



 ML> AFAIAC, the loss of that last cylinder is also "in the noise" :-(.
 ML> If I wanted to guess, I would say that the practice you describe
 ML> dates from the XT days when the last cylinder was reserved for a
 ML> test track used only by the hard-drive read/write diagnostics.  I
 ML> had a small assembly-language routine for my XT that moved the
 ML> heads over to that last cylinder before shutting down, so that if
 ML> there wasn't a smooth landing, there would be no damage to usable
 ML> data.  As I understand it, this was done automatically on the AT.
 ML> (I never owned an AT; I skipped the 286 generation as it didn't
 ML> make any sense to me.)  I would guess that hard-drive reliability
 ML> (at least for drives from reputable makers) had improved (by the
 ML> time OS/2 came along) to the point where that "test track" was
 ML> probably unnecessary, but nobody noticed it was still there until
 ML> relatively recently!

The need to reserve the last track as a test track became redundant
with the demise of ST506 drives. While I don't know the details of
EDSI so I can't comment on them, in all the ATA & SCSI drives
currently available the geometry presented to the OS bears no
relationship at all to the underlying geometry of the hardware, with
the disk controller also handling bad sector re-mapping etc.
While the reliability may have improved, the ability to use the test
track was removed by the on drive controllers.

George

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