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From: jcburt@ipsun.larc.nasa.gov (John Burton)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Danger of not parking HD?
Keywords: Error reading drive c: (Abort, Retry, Self-Destruct)?
Message-ID: <1990Oct30.145343.20085@abcfd20.larc.nasa.gov>
Date: 30 Oct 90 14:53:43 GMT
References: <795@ra.MsState.Edu> <1990Oct29.143743.23911@granite.cr.bull.com>
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In article <1990Oct29.143743.23911@granite.cr.bull.com> buck@granite.cr.bull.com (Kenneth J. Buck) writes:
>In article <795@ra.MsState.Edu> pam1@ra.MsState.Edu
>   (Phillip A. McReynolds) writes:
>>Is there much serious danger in leaving my heads unparked?
>
>This brings up a more general question upon which I am uninformed.
>Do some/all/none hard drives in use these days support autoparking heads, or
>is it still something that must be done manually?
>
>It seems that this is something which should be able to be done automatically
>upon machine shutdown (when the drive or controller detects power loss, or
>something).  I would have thought that by now, all drives would do this.
>
>What is the _real_ story here, please?

The *real* story is the differences in  technologies... The answer  to your
head parking question is yes and no...

There are two basic technologies for head positioning, stepper motor and
voice coil. Stepper motor head positioning is the cheapest and is used
on  most of the lower priced hard disks. When  the power goes off, the heads
just stay where they are, unless additional hardware is used to pull  the heads
back to their parking space (unlikely). Voice coil is more expensive (but IMHO
well  worth the extra price) and by default autoparks the heads on power  down
(when the power is removed from the voice coil, an electromagnet, the heads move
back to a base position).

If you can afford it, voice coil head positioning is the way to go. You get
automatic head parking and you *don't* have the problems of head misalignement
due to thermal expansion of the platters that can occur with stepper motor. Many
disk technicians suggest regular low level formatting of stepper motor disks
as a preventive maintenance. With voice coil, its not needed.

just my thoughts on the subject...

John Burton
(jcburt@cs.wm.edu)
(jcburt@ipsun.larc.nasa.gov)