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From: thomsen@trwspf.TRW.COM (Mark Thomsen)
Newsgroups: comp.arch
Subject: Re: What should be in hardware but isn't
Message-ID: <441@trwspf.TRW.COM>
Date: Fri, 25-Sep-87 21:41:19 EDT
Article-I.D.: trwspf.441
Posted: Fri Sep 25 21:41:19 1987
Date-Received: Sun, 27-Sep-87 09:52:28 EDT
References: <581@l.cc.purdue.edu> <18336@amdcad.AMD.COM> <582@l.cc.purdue.edu> <704@winchester.UUCP>
Reply-To: thomsen@trwspf.UUCP (Mark Thomsen)
Organization: TRW - Data Systems Lab., Redondo Beach, CA
Lines: 38

In article <704@winchester.UUCP> mash@winchester.UUCP (John Mashey) writes:
>However, the general approach (anecdotal) is not the way people design
>computers, these days, and for good reason.
>As noted before here, a plausible way to design a computer is:
>
>1) Pick a REPRESENTATIVE set of benchmarks.
>2) Do a first-cut architecture, based on past experience.
>3) Do compilers.
>4) Add or delete features, measuring the impact by running compiled/assembled
>code through architectural simulators.
>5) Iterate until you can't find anything else to add that actually
>improves performance by some noticeable amount, or until you run out of time.

I second this -- a processor design in the abstract space of "features that
are useful in current processors, that would seem to be useful, or that every
other processor has" creates the rut that the breakthrough designs have been
exploiting.  I am familiar with the MIPS, Transputer, and Lilith processors
and all three seem very efficiently designed for their role.  By efficiency
I mean speed of execution of the applications run relative to clock speeds -
as compared to competitive processors.  The Lilith for example (Wirth's
desktop marvel) is a legitimate 1 MIP workstation with a clock speed of
6.67 MHz.  Now, if you want to use it for numerical analysis it practically
grinds to a halt.  But for programming support, document production, and such
it is exceptional.  It also supports bit-map operations at 30 Mb/s.  Not bad
for its age.

Please don't go bashing the good processors of our time.  The bad processors
are so easy to pick out.  However, after weeding them out the remainders
generally have some domain of support (Unix/C, Lisp, Modula-2, assumbly
language, CAD, program development, document production, numerical analysis)
that they are quite good for.  Learn from them and sally forth to the next
generation.

This is self-serving.  I get to use the processors and I am delighted to see
what is happening.  Better and better processors are becoming available.


                                          Mark R. Thomsen