Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site utah-cs.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!houxm!vax135!cornell!uw-beaver!tektronix!hplabs!utah-cs!schimpf
From: schimpf@utah-cs.UUCP (James Schimpf)
Newsgroups: net.micro
Subject: Re: Q: Turning machines on/off frequently
Message-ID: <3040@utah-cs.UUCP>
Date: Sat, 22-Sep-84 11:36:16 EDT
Article-I.D.: utah-cs.3040
Posted: Sat Sep 22 11:36:16 1984
Date-Received: Wed, 26-Sep-84 06:42:21 EDT
References: sri-arpa.13200, <3279@ecsvax.UUCP>
Organization: Univ of Utah CS Dept
Lines: 31


       In this discussion the way light bulbs fail (i.e. when turned on)
is   mentioned  as  a  justification  for  leaving  equipment  on.    An
incandescent bulb failure ,assuming no mechanical shocks, is usually due
to  high  current  through  a  thin  spot  on  the  filament melting the
tungsten.   The  thin spot is due to the migration of the tungsten atoms
from the filament to the glass bulb (Edison Effect).  The failure occurs
at initial turn on because the metal filament has a positive temperature
coefficient  of  resistance  change.   Thus  the tungsten has its lowest
resistance  (i.e.  allowing  higher  current) when it is cold.   In IC's
there  is an analogous effect (electromigration) which affects the metal
(particularly  aluminum)  traces  on  the silicon.  IC manufacturers are
very aware of this effect so the designs compensate as much as possible.
But  if this occurs and when turned on the chip is cold then the current
surge  due to the lower resistance of the metal leads could be the final
blow.

       On the original subject most newer terminals are designed to shut
down  the  screen when not in use.  Floppy drives now stop spinning when
not  in  use.   Hard  disks  I agree are another problem but with sealed
winchesters  it seems that bearing failure is a much smaller threat than
track loss due to bouncing heads.

       Finally  my  personal  experience  with a half dozen micros which
were  left  on continuously for years has been quite good.  In that time
we lost only two dynamic ram chips and a disk controller chip.  Over 90%
of the down time was for periodic adjustment of floppy drives.

					Jim Schimpf
					CS Department University of Utah