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From: wnn@ornl.gov
Newsgroups: comp.sys.mac.hardware
Subject: Re: Leaving Mac On
Message-ID: <1991Feb11.192154.19250@cs.utk.edu>
Date: 11 Feb 91 19:21:54 GMT
References: <6140@idunno.Princeton.EDU>
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Organization: University of Tennessee/Oak Ridge National Labora
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In article <6140@idunno.Princeton.EDU> rlwald@phoenix.princeton.edu (Rob Wald)
writes:
>
>  What is the current wisdom on leaving your computer on?

The stress of thermal cycling may reduce component life if you keep turning
your computer off and on every hour.
On the other hand, most components are reated for mean time between
failure (MTBF) not taking into account how many power-on cycles you
go through. If you turn your computer off and on less than four or five times
per day, total up time probably has a greater influence on the life span of
most of the components. Many electronic components, such as CRTs or capacitors
decay over time and mechanical parts, such as disk drive bearings wear out.

At the minimum, turn your computer off over night. 
A week has 168 hours, most people work only 40 to 50 hours. So you
can expect your hardware to last about three times longer, even figuring in a
rather generous discount for thermal stress aging.

And, of course, you help conserve a lot of energy that way, which
will not only save you or your employer money, but will also help
reduce environmental impacts!

Moreover, while your computer is turned off, it is much less likely
to be damaged by a power spike.

In terms of power consumption, it is even more important that you turn laser
printers off when not in use. They generally consume much more energy than a
personal computer because they keep their fuser rollers hot all the time.
Actually, some of the older models of the HP LaserJet can even suffer damage
when left turned on for several day without use. The constant pressure and
warmth one one side of the rubber rollers causes them to be deformed.

The myth that it is better for computers to be left powered on may stem in part
from a mistaken comparison with mainframes, most of
which do batch processing during the night anyway.
Modern desktop computers are designed for frequent power cycling and they use
components that are quite different from those in their
elder brothers and sisters. Some mainframe CPU's are cooled to
cryogenic temperatures and can only stand a few dozen or hundred
cycles of warming up to room temperature and being brought down
to operating conditions again.

The entire debate reminds me a little bit of the one about fluorescent
lighting. In that case an old myth holds that restarting fluorescent
lamps takes more energy than leaving them on for several hours.
Just think how much power that would be in the couple of seconds for starting
them up and what heavy wiring it would require to supply that power. Our wall
switches and power distribution boxes would resemble a power company
switchyard!

Wolfgang N. Naegeli
President, MacClique--East Tennessee Macintosh Users Group
University of Tennessee & Oak Ridge National Laboratory
Internet: wnn@ornl.gov    Bitnet: wnn@ornlstc
Phone: 615-574-6143       Fax: 615-574-6141 (MacFax)
QuickMail (QM-QM): Wolfgang Naegeli @ 615-574-4510