"Bob Kos" wrote in message ink.net...

2) Even if you do decide to swap platters, don't sweat the dirt
too much. Scott Mueller has stated in his famous book that he
has run the same open hard drive for a long time at his seminars
with apparently little consequence. You won't be running that
long. Just be careful & neat about everything.

I've heard of people opening up drives as large as 1G, replacing the
cover, and running them for over a year, but my own luck has been much
worse, although I didn't use a clean room, just a tent, gloves, and a
baggie over my head. None of the perfectly good 120M and 200M drives
that I opened worked for more than a few hours, but a couple of 5.25"
20-30M drives on which I installed clear plastic covers worked fine.

I wouldn't trust Scott Mueller on hardware because in a very early
edition of his book he wrote that RLL 2,7 drives required plated
magnetic coatings because the oxide magnetic coatings used for MFM
drives at the time were inadequate, which wasn't true, and the real
limitation was the MFM electronics. Also, Randy Van De Loo, an
engineer who owned a hard drive repair company, Tri-Logic Systems,
back in the 1980s, wrote of Mueller:

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As far as steppers being able to only position within a single track.
Well,
this is where Mueller's lack of experience with current (since 1984)
technology starts to show. Even the venerable (read cheap) ST-225
has the
ability to micro-step in 1/2 step incrememnts as do ALL Seagate
Stepper
drives. Tandon / Western digital drives use embedded servo feedback
to
"PULL" the stepper from one phase to another like a vioce coil, to
"fine-tune" the positioning of the drives head actuator. Miniscribe's
steppers have had the ability to micro-step, although there were only
a few
models which used that ability.

The alloy used in the substrate of today's drives is based on a 5086
aluminum with a titanium and nickle clad which makes the substrate
literally
movement free in a temperature range from 50-150 degrees F. This is
in
stark contrast to the substrate used in the old 8 / 11 / 14 inch
drives
which would literally CRASH the drive when the platters would warp
when
overheated (over 120 degrees F).

As you have read above, this is not really much of a problem any
longer,
and frankly, I am quite surprised that Mueller didn't do his homework
a
little better on this subject. Given the fact that we have
complimentary
materials (which are used in both voice coil and stepper drives
alike), we
have reduced the positioning error to a couple micro-inches in all
drives.
As a matter of fact with the new high performance stepper motors being
used
in some of the newer 2.5 and 1.8 inch drives, the steppers have a
resolution
of 4,000 TPI. These drives have not yet been released to the public
yet,
but wait a few months and I am sure you will read about them in a
magazine.

I am not surprised that Mueller did not address the bit-cell
propogation
problem. After all, the problem has been around for as long as there
has
been magnetic storage devices. I can see a bit of consistency here
now.
The marketing departments of a few of the manufacturers have tried to
quell
the facts that magnetic storage media revolve around, in an attempt to
sell
the "problem free" storage device. Unfortunately, all storage devices
will
fail. Bar none. Some maybe sooner than others. If Mueller contacted
Conner Peripherals' marketing department for information to use in his
book,
he would have gotten pretty much what you have quoted here. It's far
cheaper to manufacture a drive with a voice coil actuator than it is
to put
a high performance stepper motor in it. Yes, a voice coil can move
faster,
but it is subject to a great deal more problems than a quality stepper
motor. After time, a voice coil's induction will change as it's poles
become more / less magnetized as well as the servo itself becoming
more /
less magnetized.

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