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From: hedlund@unc.UUCP (Kye Hedlund)
Newsgroups: net.arch
Subject: Mips / MHz
Message-ID: <1363@unc.unc.UUCP>
Date: Mon, 21-Apr-86 08:29:32 EST
Article-I.D.: unc.1363
Posted: Mon Apr 21 08:29:32 1986
Date-Received: Thu, 24-Apr-86 06:21:07 EST
Distribution: net
Organization: CS Dept, U. of N. Carolina, Chapel Hill
Lines: 35

When comparing the perofrmance of microprocessor architectures, it would
be desirable to separate architectural factors from technological
factors. For example, if machine A has performance 1.0 and machine B
has performance 2.0, does B have a "faster architecture?"  The answer of
course is "it depends."  It depends on many factors including the
underlying technology used to fabricate the chip.  If B was implemented
in 1.0um CMOS and runs off a 20MHz clock whereas A was fabricated with 
4um nMOS and runs at 5MHz then perhaps the architects (and 
implementors) of A did an excellent job with a slower technology.
Perhaps A will run circles around B if implemented with similar 
technology.

This leads us to making a first attempt at factoring out the technology
speed out of performance estimates of microprocessors by computing
performance/MHz.  Mips/MHz immediately comes to mind but one could
also compare Drystones/MHz, Whetstones/Mz, etc.

This measure is clearly far from precise.  Performance ratings are subject
to interpretation and variation.  MHz is by no means a complete
measure of the underlying circuit technology.  Drystones and Whetstones
also measure the quality of code produced by the compiler, etc., etc, etc.
We could generate hundreds of net messages thinking of other shortcomings.

BUT, a 68010 is about 0.4 mips @ 10MHz, and a 68020 is about 1.5mips @
16.67MHz (measured on SUN workstations running C under 4.2 BSD).
This gives 0.040 mips/MHz for the 68010 and 0.091 mips/MHz for the 68020
and suggests that there is better than 2:1 architectural and implementation
advantage for the 68020 independent of the circuit technology.

---- Kye S. Hedlund
     Dept. of Computer Science
     U. of North Carolina
     Chapel Hill, NC  27514

     CSNet:  hedlund@unc