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From: brucek@hpsrla.HP.COM (Bruce Kleinman)
Newsgroups: comp.arch
Subject: Re: Re: really CISC (was: Japanese 32-bit CPUs ( NEC V70 ))
Message-ID: <3460002@hpsrla.HP.COM>
Date: Fri, 22-May-87 15:18:04 EDT
Article-I.D.: hpsrla.3460002
Posted: Fri May 22 15:18:04 1987
Date-Received: Sun, 24-May-87 01:40:56 EDT
References: <692@cpocd2.UUCP>
Organization: Network Measurements Div - Santa Rosa, CA
Lines: 35


+---------
| Last time I looked, every CISC microprocessor ever made spent
| 50% to 75% of the chip area on control, with an average of about 2/3.
| [....]
| This leaves only 25% to 50% of the chip to do useful work.
+---------

My point exactly.  Consider the newest Transputer, the T8 I believe.
A RISCy chip which happens to be microcoded, curiously enough.  Very
tight instruction set, and a stack-like programming model.  Fixed-width
instructions, a scant 8 bits wide.  Honest.  Sound simple?  It is.

The instruction decode and microcode occupy about 10% of the die.  Hmmm,
what to do the rest of that real estate.  The Inmos folks decided on
4K bytes of RAM, a floating point unit, a DRAM controller, and four
high-speed serial links.  They have experimented with a version that
replaces the floating point unit with a Winchester controller.

My point here is not to glorify the Transputer (although I am exceedingly
impressed by the chip).  I use it to illustrate the possibilities opened
up by "simple instruction set computers" as a whole.  MIPS II has a
4K byte cache.  The AMD 29000 has a 192 registers, a branch target cache,
and an MMU.  The Fairchild Clipper has a floating point unit (the 8K bytes
of cache and the pair of MMUs are on two separate dies).  The possibilities
seem nearly endless.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                              Bruce Kleinman
              Hewlett Packard -- Network Measurements Division
                          Santa Rosa, California

                         ....hplabs!hpsrla!brucek
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~