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From: aad@stepstone.com (Anthony A. Datri)
Newsgroups: comp.sys.sun
Subject: Re: Is RISC faster
Message-ID: <2820@stpstn.UUCP>
Date: 22 Feb 89 11:18:22 GMT
References: <15686@mimsy.UUCP>
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Original-Date: 13 Feb 89 18:38:08 GMT
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In article <15686@mimsy.UUCP> folta@tove.umd.edu (Wayne Folta) writes:

>A co-worker and I were debating why RISC machines might be faster than
>CISC (traditional) machines.  I had just read an article that did some
>UNIX benchmarks, and found RISC machines ran about 3 times faster than
>CISC (a 68030-based machine, for example).

*WHICH* RISC machine?  RISC is a general description of a style processor
design, not a specific implementation.

>The question is why.  I had assumed that a RISC machine had a much smaller
>and simpler instruction set.  That is, fewer instructions, each of which
>did simpler things than a CISC instruction set.

True.

>But how can this make a
>machine that much faster?  Is it because most CISC machines are
>microcoded?

I think microcoding is a seperate issue.  One of the usual ideas about
RISC machines is that all instructions execute in one cycle.

>It seems to me that to accomplish the same work, the RISC machine would
>just have to execute more instructions than the CISC machine.

It often will.  The idea is that you get a code generator that is really
smart, and can output code that does fewer unnecessary things than your
average ciscish code.  I've heard that IBM's PL.8 compiler is one such.
But on the other hand, your executables are often bigger, and that means
you should have more memory, bigger disks, and that you spend more time
paging and swapping things around.

Followups to comp.arch

[[ Agreed!  Usenet people, please follow up to comp.arch.  Non-Usenet
people, I don't think there is a suitable forum.  --wnl ]]

Anthony A. Datri @SysAdmin(Stepstone Corporation) aad@stepstone.com stpstn!aad