Murray Lesser wrote to Will Honea on 12-02-1999

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
ML> describe dates from the XT days when the last cylinder was reserved
ML> for a test track used only by the hard-drive read/write diagnostics.
ML>  I 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 make
ML> any sense to me.)  I would guess that hard-drive reliability (at
ML> least for drives from reputable makers) had improved (by the time
ML> OS/2 came along) to the point where that "test track" was probably
ML> unnecessary, but nobody noticed it was still there until relatively
ML> recently!

According to Sam Detweiler of IBM, this was originally a parking zone
but like so many things it got built into other unrelated programs. 
Specifically, it was used for destructive read/write/read testing in
some diags that IBM used for their PC's.  So we have 1 cylinder at
either end of the drive that is possibly wasted - mousefarts in a
hurricane.  But as the politician said: "a trillion here, a trillion
there; pretty soon we're talking about some real money!"

Will Honea 
--- Maximus/2 2.02