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From: fouts@orville.nas.nasa.gov (Marty Fouts)
Newsgroups: comp.arch
Subject: Re: Power vs number of circuits
Message-ID: <2957@ames.arpa>
Date: Thu, 1-Oct-87 17:39:01 EDT
Article-I.D.: ames.2957
Posted: Thu Oct  1 17:39:01 1987
Date-Received: Mon, 5-Oct-87 07:36:14 EDT
References: <732@obiwan.UUCP>
Sender: usenet@ames.arpa
Reply-To: fouts@orville.nas.nasa.gov.UUCP (Marty Fouts)
Lines: 22

In article <732@obiwan.UUCP> mark@mips.UUCP (Mark G. Johnson) writes:
>In article <2934@ames.arpa>, lamaster@pioneer.arpa (Hugh LaMaster) writes
>	> Current Cray technology is a 250MHz processor.  Try clocking
>	> your 68020 or MIPS machine at that speed and see how long it
>	> takes to melt.
>
>In the MIPS CPU case, about 3/4 of its 2W power dissipation (at 60 ns
>cycle) is due to switching (power = C*V*V*f).  However, assume the worst,
>that ALL power consumption is due to switching transients.  Then you
>just scale by (60ns / 4ns) and find that its power at 250 MHz would
>be 30 Watts.  Since it's now a Cray-class device, it gets to use a
>Cray-sized 50 ton refrigeration unit, so 30 Watts should be no problem :-).
>

Shouldn't you be taking the increase in volume of circuitry into
account?  After all, MY Cray 2 has 2 gigabytes of memory in the same
cabinetry as 4 CPUs.  The total effect that the added part count has
on power dissipation through can be estimated by multiplying 30 watts
by 120000 (the number of parts in a Cray 2 CPU) and dividing by
whatever the number of components in a MIPS CPU case are.  Since I
don't know this number I'll just divide by 100 and come up with 36
KWatts, which is slightly higher than your estimate.