Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!elroy.jpl.nasa.gov!swrinde!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!unixhub!slacvm!dbg
From: DBG@SLACVM.SLAC.STANFORD.EDU
Newsgroups: comp.sys.mac.hardware
Subject: Leave the Mac on
Message-ID: <91053.130639DBG@SLACVM.SLAC.STANFORD.EDU>
Date: 22 Feb 91 21:06:39 GMT
Organization: Stanford Linear Accelerator Center
Lines: 38

Hard drive bearings gradually fail while the drive is not spinning.
Vibrations from the environment polish (brinnell) the contact areas
on the ball bearing races, and this eventually causes the bearing
to vibrate during operation.

ICs usually fail during on/off thermal transients. The chip material
and package material are not perfectly matched for thermal expansion,
so temperature changes cause small relative motions that cause cracks
to grow from the rough edges of the chip into the working areas.

I estimate that about 90% of the failures I have seen in personal-
computer-like equipment have occurred during power on/off transitions.
Machines that are turned off overnight fail noticeably more often.

When you consider the environmental impact of leaving the mac powered
up, you should also consider the cost in energy of replacing failed
parts (usually a whole board is discarded and replaced). This cost is
generally proportional to the price of the board (energy is an important
part of the cost of anything if you follow the components back far
enough in their production).

You also have to consider the value of your time for recovering from
the equipment failure.

I leave my Macs on all the time unless I know a power outage is
scheduled (an unsupervised restart destroyed my Jasmine 80 when
head stiction stalled the disk rotation, and heat buildup over
several days baked the disk into oblivion). I do power off my
LaserWriter overnight, though I wonder if even that energy saving
is worth it. Yes, I do pay my own electric bills (and repair bills).
I now use an uninterruptable power supply to avoid unsupervised
restarts of my hard drives and to keep my faxmodem up at all times.

-- David B. Gustavson, Computation Research Group, SLAC, POB 4349 MS 88,
    Stanford, CA 94309   tel (415)926-2863  fax (415)961-3530
-- What the world needs next is a Scalable Coherent Interface!
-- Any opinions expressed are mine and not necessarily those
   of the Stanford Linear Accelerator Center, the University, or the DOE.