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From: brooks@lll-crg.ARpA (Eugene D. Brooks III)
Newsgroups: net.arch
Subject: Re: Cray-2 impressions
Message-ID: <919@lll-crg.ARpA>
Date: Wed, 16-Oct-85 00:07:49 EDT
Article-I.D.: lll-crg.919
Posted: Wed Oct 16 00:07:49 1985
Date-Received: Thu, 17-Oct-85 02:06:06 EDT
References: <1189@ames.UUCP> <224@well.UUCP>
Reply-To: brooks@lll-crg.UUCP (Eugene D. Brooks III)
Distribution: net
Organization: Lawrence Livermore Labs, CRG Group
Lines: 27

>Gene:
>  Is it true that the CRAY-2 cpu is really a CRAY-1  (not an X-MP)
>cpu, meaning that it has only one path to memory and doesnt do
>chaining?
Yes, it true.

>So the only major speedup between the X-mp and -2
>cpu's is the faster clock cycle of the 2,  4.1 ns.
yes

>Also, I understand that the 256K 64-bit memory is slower than the
>memory on the x-mp, but there is a fast 16K memory cache per processor.
Yes, the latency of the main memory is a real problem.

>So it really looks like a CDC 7600!!
I'm sure you would prefer the Cray 2.  The user does not
see the 16k local memory, the compiler does.

>I'd like to see some comparison timings between the x-mp and the 2.
When the xmp is benchmarked against the 2 the xmp usually wins unless
one can manage to effectively buffer vectors through the 16k cache and
make a lot of uses of the vector data.  If the cache can't be effectively
used and the 3 port architecture is useable on the the loop the xmp
wins.

PS  I haven't heard of a single person who has stood in the middle of the
Cray 2 and was not impressed.