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