Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!gatech!gitpyr!loligo!mccalpin
From: mccalpin@loligo.uucp (John McCalpin)
Newsgroups: comp.arch
Subject: Re: Don't look back
Message-ID: <7367@pyr.gatech.EDU>
Date: 24 Feb 89 15:26:10 GMT
References: <20667@lll-winken.LLNL.GOV> <7330@pyr.gatech.EDU> <656@m3.mfci.UUCP>
Sender: news@pyr.gatech.EDU
Reply-To: mccalpin@loligo.cc.fsu.edu (John McCalpin)
Organization: Supercomputer Computations Research Institute
Lines: 35

In article <656@m3.mfci.UUCP> colwell@mfci.UUCP (Robert Colwell) writes:
>In article <7330> mccalpin@loligo.cc.fsu.edu (John McCalpin) writes:
>>
>>I don't mean to pick on CDC/ETA --- even the fastest Cray's are going
>>to get caught by the highest performance RISC chips pretty soon.
>
>A note from the other side of the aisle.  "Even the fastest Crays"?  Are
>you kidding?  If you believe the Cray-3 is going to be manufacturable
>(an entertaining discussion all by itself) then how the heck do you think
>a micro is going to get 1800 mflops any time soon?  I think that's wishful
>thinking or outright fantasy. 
>Bob Colwell               ..!uunet!mfci!colwell

If you re-read my original message, you will see that I am talking about 
SCALAR code only.  Comparing the performance of EXISTING Cray machines
to the fastest RISC chips show that the Whetstone performance of a 
Cray X/MP is not that much faster than a 25 MHz MIPS R-3000/3010
(or an MC88000). Cray may have a factor of 2 better performance (I
don't have the numbers right in front on me), which I again claim is
not impressive when the clock speeds (118MHz vs 25 MHz) and prices
($3,000,000+ vs $150,000) are taken into consideration.  Not all the
important codes in the world can be vectorized to any significant degree.

I certainly agree with you that micros will never compete with the 
VECTOR performance of these machines simply because the memory
bandwidth is not going to be available.   For my large scientific 
problems (which are >98% vector code), I much prefer the CDC memory-
to-memory approach.  Having a data cache would be very little help.
However, Cray and CDC/ETA machines are not likely to ever be cost-
effective on scalar codes, precisely because most of their budget
goes into producing huge bandwidth memory subsystems....
----------------------   John D. McCalpin   ------------------------
Dept of Oceanography & Supercomputer Computations Research Institute
mccalpin@masig1.ocean.fsu.edu		mccalpin@nu.cs.fsu.edu
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