Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!zaphod.mps.ohio-state.edu!mips!ultra!shj
From: shj@ultra.com (Steve Jay)
Newsgroups: comp.arch
Subject: Re: Why The Move To RISC Architectures?  ('386 vs. RISC)
Message-ID: <1990Mar22.184122.7917@ultra.com>
Date: 22 Mar 90 18:41:22 GMT
References: <28012@cup.portal.com> <1990Mar20.175843.2612@utzoo.uucp> <5303@scolex.sco.COM> <1268@m3.mfci.UUCP>
Organization: Ultra Network Technologies
Lines: 32

colwell@mfci.UUCP (Robert Colwell) writes:

>>Well, I'd say more than that, about 25 years.  Seymour Cray and the CDC
>>Cyber 6600, a truly wonderful machine with less than 74 instructions, a
>>load-store architecture, and three-operand instructions.  Just beautiful.

>An amazing machine.  But unless we know more about how it shared 
>responsibility for performance with its compiler, I refuse to call
>it a RISC.  From what I've read, it was designed so that the hardware
>would extract whatever parallelism it could use, and all the compiler
>did was convert the high level source into sequential machine ops.

The original compiler for the 6600, called "RUN", made no attempt
to optimize instruction sequences.  By 1970, however, CDC had a new
compiler, FTN, which did rearrange instructions to optimize usage
of the multiple functional units.  The technology of both local and
global optimization in the FTN compiler was continously improved,
and by mid to late 70's, it was difficult to beat the compiler even
with hand tuned assembly language.

I don't think the unavailability of an optimizing compiler when the
6600 first came out in any way detracts from the RISCness of the
machine.  You can read articles written around 1965 which justify
the design decisions for the 6600 in terms almost identical to those
used today to justify RISC over CISC.  I suspect that experiences with
the 6600/7600 were important in teaching later architects how important
compiler technology is.

Steve Jay
shj@ultra.com  ...ames!ultra!shj
Ultra Network Technologies / 101 Dagget Drive / San Jose, CA 95134 / USA
(408) 922-0100 x130	"Home of the 1 Gigabit/Second network"