Path: utzoo!mnetor!uunet!husc6!bu-cs!madd
From: madd@bu-cs.BU.EDU (Jim Frost)
Newsgroups: comp.sys.ibm.pc
Subject: Re: RESET BUTTONS AND HARD DISKS
Message-ID: <19876@bu-cs.BU.EDU>
Date: 12 Feb 88 15:12:35 GMT
References: <3505@batcomputer.tn.cornell.edu> <-497141@cpedev> <662@gethen.UUCP> <19824@bu-cs.BU.EDU> <1691@mipos3.intel.com>
Reply-To: madd@bu-it.bu.edu (Jim Frost)
Followup-To: comp.sys.ibm.pc
Organization: Boston University Distributed Systems Group
Lines: 34

In article <1691@mipos3.intel.com> dbraun@cadev4.UUCP (Doug Braun ~) writes:
>In article <19824@bu-cs.BU.EDU> madd@bu-it.bu.edu (Jim Frost) writes:
>>I recall a time back in the CP/M days when a drive that just dropped
>>the heads was turned off before doing a power down sequence.  The
>>noise that that thing made was enough to make anyone cry.

>The noise mentioned above is undoubtedly due to a mechanical brake
>that stops the rotating disks ASAP after power-off.  Some drives
>have a brake with a little solenoid pulls the brake pad away
>from the motor rotor when power is applied.  Other drives use a relay
>to short out the motor coils when power is removed, electrically
>braking the motor.

The noise I mentioned was of the heads destroying the surface of the
disk.  The drive was destroyed, a cost of several thousand dollars at
the time, not to mention the loss of data.

As for whether or not the drive heads actually touch the disk, I
suppose you're right that they do on cheap drives, but the only drives
I've worked on that appeared to do this were really old drives on an
AT.  They made an obvious "clunk" during spin down that always made me
jitter.  But recently I've been working with drives of 80 meg and
up....

>Take apart a few of these beasties, and you'll know what's
>REALLY going on.

I liked it better when they encased drives in clear plastic so you
could watch 'em run.

Cheers,

jim frost
madd@bu-it.bu.edu