Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Why The Move To RISC Architectures?  ('386 vs. RISC)
Message-ID: <1990Mar20.175843.2612@utzoo.uucp>
Organization: U of Toronto Zoology
References: <28012@cup.portal.com>
Date: Tue, 20 Mar 90 17:58:43 GMT

In article <28012@cup.portal.com> Will@cup.portal.com (Will E Estes) writes:
>What is the MIPS rating of these microprocessors:
>
>386SX-15
>386-20
>386-25
>386-33

With what memory systems, and running what workload?  And which flavor of
"MIPS" are you talking about?

>Also, since the 80386 has a more complex instruction set and does
>more work in a given instruction than does a typical RISC chip,
>does comparing MIPS figures between RISC and non-RISC
>architectures really tell you anything of worth?

Comparing MIPS figures tells you nothing of worth even when those
complications aren't present.  MIPS numbers are marketing nonsense, not
useful performance measures.

>Finally, why is everyone so excited about RISC?  Why the move to
>simplicity in microprocessor instruction sets?  You would think
>that the trend would be just the opposite - toward more and more
>complex instruction sets - in order to increase the execution
>speed of very high-level instructions by putting them in silicon
>and in order to make implementation of high-level language
>constructs easier.

Oh my, a newcomer to the group, I'd say...  RISC is exciting because it
generally leads to computers that run real workloads faster.  That is
the meaningful measure of performance.  The fact is, trying to bundle
zillions of instructions onto the chip usually makes them slower, and
compilers find it very difficult to effectively exploit all the bizarre
silliness that CISC designers throw in.  About a decade ago, it started
to become clear that executing simple instructions very quickly works
much better.
-- 
MSDOS, abbrev:  Maybe SomeDay |     Henry Spencer at U of Toronto Zoology
an Operating System.          | uunet!attcan!utzoo!henry henry@zoo.toronto.edu