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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.arch
Subject: Re: What with these Vector's anyways?
Message-ID: <8344@utzoo.UUCP>
Date: Thu, 23-Jul-87 13:29:55 EDT
Article-I.D.: utzoo.8344
Posted: Thu Jul 23 13:29:55 1987
Date-Received: Thu, 23-Jul-87 13:29:55 EDT
References: <218@astra.necisa.oz> <142700010@tiger.UUCP>, <363@astroatc.UUCP>
Organization: U of Toronto Zoology
Lines: 16

> BTW:  The Cray-1 & XMP are also very-good Scalar machines!

It should be noted that this is an important reason why they sell so well
(the Cray production runs are an order of magnitude larger than those of a
lot of other supercomputer projects in the last two decades).  If a program
is 90% vectorizable, than magically making the vector part of it *infinitely*
fast will only speed it up by a factor of ten.  Too many of the pre-Cray
supercomputers did vectors really fast but were pigs on scalar computation.
Cray's secret is that its machines are blindingly-fast *scalar* engines that
sort of incidentally happen to do vectors even faster.  For some reason :-),
saying "our machines run your code real fast if you rewrite it somewhat"
doesn't have nearly the customer appear of saying "our machines run your
code real fast -- even faster if you rewrite it somewhat".
-- 
Support sustained spaceflight: fight |  Henry Spencer @ U of Toronto Zoology
the soi-disant "Planetary Society"!  | {allegra,ihnp4,decvax,utai}!utzoo!henry