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From: jso@edison.UUCP (John Owens)
Newsgroups: net.micro.pc
Subject: Re: Hard disk shutoff
Message-ID: <879@edison.UUCP>
Date: Mon, 20-Oct-86 12:40:54 EDT
Article-I.D.: edison.879
Posted: Mon Oct 20 12:40:54 1986
Date-Received: Wed, 22-Oct-86 22:25:29 EDT
References: <12068@watnot.UUCP>
Distribution: net
Organization: General Electric Company, Charlottesville, VA
Lines: 49
Summary: hard disks are meant to run continuously

In article <12068@watnot.UUCP>, rdgreenall@watnot.UUCP (Richard Greenall) writes:
> I am wondering if the constant running of the hard disk is damaging to
> it. (Ex.  running approximately 20 hours. per day.)

>      It seems crazy to me that the hard disk should be running 
> when there is no activity on the board.  The
> ideal situation  would be for the pc to start the motor on the 
> hard disk as soon as it detects a call on the modem. (I think this 
> is impossible but who knows what somebody can come up with)

I can see where you are coming from, but this would be worse, for a
number of reasons.

1) Although the heads contact the disk surface for floppies, for hard
disks they fly above the surface of the disk, separated by a small air
space.  There is no wear on the surface on the disk while it is
spinning or being accessed.

2) A hard disk has a lot of inertia.  When you start the motor on a
floppy drive, the system typically waits for a second or less for the
floppy to "come up to speed".  This can take up to a minute on a
typical small (20MB) hard disk.  Even after this amount of time, the
rotational speed won't be quite as stable as it will after it has been
running for a long period of time.

3) The shocks to the drive mechanism and to the disk platters
themselves from slowing down, stopping, and coming back up to speed
are significant.  They can, after time, cause mechanical problems and
can knock loose any foreign particles that might be safely tucked in a
crevice somewhere.

4) Winchester-type disks are *designed* to be constantly running.  On
large multi-user systems, with disks up to 14" in diameter, the drives
run 24 hours a day, 365 days a year, constantly; "spinning down" the
disk is a rare event.  When designing hard disks for microcomputers,
the designers have to take into account that the disk will be powered
up and down quite often (once or twice a day), and make it more rugged
to withstand that.

In summary, please *don't* try to start and stop your hard disk like
that.  And for anyone who has a system with a hard disk: don't turn it
on and off many times a day if you can help it.  I have an XT that I
turn on and off daily, and an AT that has been running for months
without being powered down.  (The AT is running XENIX, and I want to
leave it up at all times to pick up mail and such.)

John Owens		General Electric Company - Charlottesville, VA
jso@edison.GE.COM	old arpa: jso%edison.GE.COM@seismo.CSS.GOV
+1 804 978 5726		old uucp: {seismo,decuac,houxm,calma}!edison!jso