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From: lamaster@pioneer.arpa (Hugh LaMaster)
Newsgroups: comp.arch
Subject: Re: What with these Vector's anyways?
Message-ID: <2413@ames.arpa>
Date: Tue, 28-Jul-87 14:06:41 EDT
Article-I.D.: ames.2413
Posted: Tue Jul 28 14:06:41 1987
Date-Received: Thu, 30-Jul-87 00:40:54 EDT
References: <218@astra.necisa.oz> <142700010@tiger.UUCP>
Sender: usenet@ames.arpa
Reply-To: lamaster@ames.UUCP (Hugh LaMaster)
Organization: NASA Ames Research Center, Moffett Field, Calif.
Lines: 65
Keywords: vector Cray Cyber CDC Cpu Supercomputers

In article <10883@amdahl.amdahl.com> chuck@amdahl.UUCP (Charles Simmons)
writes:

>In article <2408@ames.arpa> lamaster@ames.UUCP (Hugh LaMaster) writes:

>>A vector machine is NOT the same thing as a SUPERCOMPUTER.  A supercomputer is
>>a loose term generally applied to this year's two or three fastest (usually
>>vector) or most expensive (:-) machines.

> ...   in my experience
>the term supercomputer is only applied to extremely fast scalar processors
>with attached vector processors.  For example, people around here tell
>me that an Amdahl 5890 is at least as fast as a Cray (which one?) for
>scalar processing.  However, a 5890 is "only" a mainframe and not a
>supercomputer.  I think if you attach a vector processor to a 5890, however,
>you do end up with a supercomputer.

There are several points here.  The first is that "scalar" means several
things.  To some people it means the speed that that the O/S kernel will run.
To others, it means the speed that a small sort, or other "small" data
intensive application will run.  To others, it means floating point code that
is not vectorizable.  All of these are different.  A subsequent poster
mentioned Dhrystone, for example, which is very string intensive and does no
floating point; this is not the same "scalar" that a typical Cray user is
thinking of ("My Monte-Carlo code runs in scalar...").  When typical
supercomputers are touted as good scalar machines, it is with reference to the
third version of "scalar" above, not the first.  It is worth noting, though,
that for many years supercomputers from CDC and Cray were fastest in all three
categories.

The second point is that there are many other supercomputer designs besides
vector machines.  A list of them all would be exhausting to read.  It so
happens that the only really successful machines to date have been vector
machines.  In the future?  A matter of intense debate :-)

The third point, is, that I have mentioned previously, vector capability is a
cost effective thing to add to minicomputers, and now microcomputers, that are
intended for engineering, scientific, and graphics uses.  Even though it
doesn't make Dhrystone run any faster.

It is also worth noting that there are other operations besides floating point
that can be vectorized.  In particular, bitwise logical operations are useful
for image processing/graphics, and encoding/decoding.  Vector instructions
allow these operations, which can be done in one instruction, and which are
thus candidates for a RISC machine, to proceed at (say) one per CPU cycle, on
a system where the CPU cycle speed is significantly faster than memory speed
(the memory bandwidth on these machines is provided with multiple banks).  So,
vectorization is not restricted to floating point, and can pay off on even
some very simple "one cycle" instructions.






  Hugh LaMaster, m/s 233-9,  UUCP {seismo,topaz,lll-crg,ucbvax}!
  NASA Ames Research Center                ames!pioneer!lamaster
  Moffett Field, CA 94035    ARPA lamaster@ames-pioneer.arpa
  Phone:  (415)694-6117      ARPA lamaster@pioneer.arc.nasa.gov


                 "IBM will have it soon"


(Disclaimer: "All opinions solely the author's responsibility")