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From: bcw@rti.rti.org (Bruce Wright)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Why The Move To RISC Architectures?  ('386 vs. RISC)
Summary: Mips and hype
Message-ID: <3685@rtifs1.UUCP>
Date: 22 Mar 90 22:08:51 GMT
References: <28011@cup.portal.com> <40970054@hpindda.HP.COM> <2607b76e.5ca0@polyslo.CalPoly.EDU>
Organization: Research Triangle Institute, RTP, NC
Lines: 34

In article <2607b76e.5ca0@polyslo.CalPoly.EDU>, jdudeck@polyslo.CalPoly.EDU (John R. Dudeck) writes:
> 
> A few weeks ago I made the remark on the net that it seems meaningless to
> compare RISC MIPS with CISC MIPS.  I was soundly rebutted by any number
> of netters telling me that all the manufacturers use VAX MIPS
> when rating their cpu's.  In other words, benchmarks are run for various
> types of cpu-intensive applications, and the results are compared to the
> same benchmarks on a VAX 11/780, which is the platinum standard by which
> all cpu's are measured.

Unfortunately, although this might be useful in some situations, it is
too often abused:  the manufacturer tries a number of benchmarks, and
advertizes the one that shows his machine off the best, as if it were
the typical case rather than the best case.  Unfortunately, not all
machines perform their operations with equal efficiency - even VAXes
don't all execute all their instructions in times that are simple
multiples of each other.  And we are probably all aware of how far off
things like the Norton SI index are for PC's.  This is even worse when
you are talking about machines with such drastically different machine
architectures as a VAX and a RISC machine - sometimes you can find
situations where a single VAX instruction -> a single RISC instruction,
and other times a VAX instruction -> several dozen (or hundred) RISC
instructions.  Comparison for all possible applications is extremely
difficult, which enhances the probability that at least one benchmark
will show off one machine particularly well against another.

And, of course, sometimes machines and compilers are designed with a
particular benchmark _in mind_, resulting in even more anomolous
results.

In fairness this isn't new with the RISC-CISC debate - it's a tradition
that's been going on for decades.

						Bruce C. Wright