OT: the 1U system

From: Jeffrey S. Worley <Technoid_at_30below.com>
Date: Thu Jan 30 14:02:00 2003

Tony gets a cigar!

Yes. It is true that hard disk makers didn't warrant drives that were
installed in funny positions such as on their face's or corners or
whatnot. These days though it seems you could mount one on any angle
you like. I've seen lots of machines with drives mounted with their
'faces' down.

Back in the day, drives relied on a passive stepper scheme for
alignment. These days, the stepper is replaced by a voice coil similar
to a speaker's cone. The coil throws the arm around and the arm's
pickup(s) 'sniff' at pre-coded positioning information on the disks to
fine-tune the coil's final location.

I think the reason for the switch to voice coils+wedge-servo encoded
positioning was a function of cost. It takes some local intelligence on
the part of the hard disk to do all that and in the early days it was
just too expensive.

One of the first drives I'm aware of that used this method was the
popular server drive by Seagate. The ST4096. It differs from today's
drive by having dedicated a whole platter to the wedge positioning
information. Now they use something called 'embedded servo' where the
positioning 'map' is factory encoded on the same platter(s) that user
data is stored.

Regards,

Jeff

-----Original Message-----
From: cctalk-admin_at_classiccmp.org [mailto:cctalk-admin_at_classiccmp.org]
On Behalf Of Tony Duell
Sent: Thursday, January 30, 2003 2:24 PM
To: cctalk_at_classiccmp.org
Subject: Re: OT: the 1U system

> Folklore for PC's was that if you recorded data on a hard drive with
the
> platters horizontal, remounting it vertically could cause read errors.
Any
> truth to this?

It might be true for the old hard drives that used stepper motor
positioners, or some other system where the positioning was 'absolute'
rather than taking a position reference (servo) signal off the platters.

With those drives, the force of gravity on the head assembly might move
it slightly off-track.

Servo-tracked drives position the head by reading signals off the
platters, and will correct automatically for gravity, etc.

-tony
Received on Thu Jan 30 2003 - 14:02:00 GMT