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From: AKONSTAM@TRINITY.BITNET (AARON KONSTAM)
Newsgroups: comp.sys.sun
Subject: Re: Is RISC faster
Message-ID: <8902131837.AA10519@rice.edu>
Date: 22 Feb 89 10:58:11 GMT
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Original-Date: Mon, 13 Feb 89 10:30:43 CST
X-Sun-Spots-Digest: Volume 7, Issue 164, message 3 of 9

<Wayne Folta asks: Is Risc faster? (V7n142)

The best place to find a clear and concise expalnation of why RISC
machines are faster than CISC machines in the first two chapters of the
book, "RISC Architecture"  by Daniel Tabak, Research Studies Press(John
Wiley ,1987).  Briefly the reasons are as follows:

a. 10% of the RISC chip is taken up with the control unit as opposed to
60% of the area of the MC68000. There are only a very few instructions
(about 30 on most RISC machines) which execute in one clock cycle. They
are fast enough that a set of RISC instructions that do the same job as
one 68000 instruction execute faster than the 68000 instruction.

b. RISC machines are however much slower in doing things like floating
point instructions so they cheat and have floating point coprocessors to
do the floating point arithmetic.

c. The rest of the area on the RISC cpu chip are taken up by a larger
number of registers. This allows more register-register processing instead
of register-memory processing.

d. Each process is given a register window for its local variables.  These
widows are made to overlap so that a calling process shares resgisters
with the process it calls. By means of these shared registers arguments
are passed between the processes (or really not passed so calls are
executed faster).  Ther is more to be said about this but I hope this is
helpfull.

AARON KONSTAM
Trinity University
715 Stadium Dr.
San Antonio, Tx 78284
(512)-736-7484
AKONSTAM.TRINITY.BITNET