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From: gillies@m.cs.uiuc.edu (Don Gillies)
Newsgroups: comp.sys.mac.hardware
Subject: Re: Leave the Mac on
Message-ID: <1991Feb28.204601.31131@m.cs.uiuc.edu>
Date: 28 Feb 91 20:46:01 GMT
References: <91053.130639DBG@SLACVM.SLAC.STANFORD.EDU> <1991Feb28.050936.6830@m.cs.uiuc.edu>
Organization: University of Illinois, Dept. of Comp. Sci., Urbana, IL
Lines: 34

Oops, that last paragraph was a little incoherent.  Let's try again.

On the savings side, small PC's (mac SE, SE/030) consume 60 watts of
power when turned on and add to air conditioning (power consumption at
UIUC was determined empirically with electrical measuring devices).
Big PC's (Mac II, IBM PS/2 50, 70) take more than 110 watts when
turned on, and add proportionately more to air conditioning costs.
For a Mac II, at 8c/kilowatt-hr, the cost of leaving it on is $58.60 a
year in wasted electricity (assuming a 40-hour work week, i.e. a
128-hour waste week).  My Mac II has been cycled an average of 2-3
times daily for 3.5 years with a Quantum-80 5" disk drive, and has
never exhibited trouble.  The savings are even greater if you consider
the reduced air conditioning.

I would think that motor failure is the most improbable failure mode
for a hard disk.  More likely is media failure (magnetic oxide being
scraped from the disk platter), stepper-motor failure (failure of
the disk arm to be able to move correctly over the surface of the
disk), or electronics failure (failure of the controller chips).

Also, it may well be that conservation minded people cannot afford to
buy the highest quality machines and blow the power to keep them
running all the time.  The cheapest hard disks on the market use the
lowest quality components and exceed manufacturer's specs by the
smallest margins (this is a quote from a friend of mine who does
reverse-engineering for the #1 hard disk maker in the world).

Don Gillies	     |  University of Illinois at Urbana-Champaign
gillies@cs.uiuc.edu  |  Digital Computer Lab, 1304 W. Springfield, Urbana IL
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"UGH!  WAR! ... What is it GOOD FOR?  ABSOLUTELY NOTHING!"  
	- the song "WAR" by Edwin Starr, circa 1971

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