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From: ian@argosy.UUCP (Ian L. Kaplan)
Newsgroups: comp.arch
Subject: parallel systems vs. uni-processors
Message-ID: <308@argosy.UUCP>
Date: 17 Oct 89 20:39:54 GMT
References: <35825@lll-winken.LLNL.GOV> <20336@princeton.Princeton.EDU>
Sender: news@argosy.UUCP
Reply-To: ian@bear.UUCP (Ian L. Kaplan)
Organization: MasPar Computer Corporation, Sunnyvale, CA
Lines: 55

In article <20336@princeton.Princeton.EDU> mg@notecnirp.edu (Michael Golan) writes:
>Last year, I took a graduate level course in parallel computing here at
>Princeton. [...]
>
>1) There is no parallel machine currently the works faster than non-parallel
>machines for the same price. The "fastest" machines are also non-parallel - 
>these are vector processors.
>

  Clearly this is proof that a little knowledge is a dangerous thing.  

  Even n-cube machines run applications like Monte Carlo simulation
with _much_ better price performance than supercomputers.  Now it
might be claimed that this is a special class of applications.
However parallel processors are not limited to n-cubes.  The
Connection Machine has beaten Cray machines on a number of classic
vectorizable codes (e.g., fluid flow).  For reference see "Proceedings
of the Conference on Scientific Applications of the Connection
Machine", 1988, Edited by H. D. Simon, World Scientific press.  Note
that the Connection Machine is probably less than half the cost of the
Cray.  I am sure that even cheaper SIMD processors will appear in the
near future.

>2) A lot of research is going on - and went on for over 10 years now. As far
>as I know, no *really* scalable parallel architecture with shared
>memory exists that will scale far above 10 processors (i.e. 100). And
>it does not seems to me this will be possible in the near future.

  By this narrow deffinition, the statement is more or less correct.
Classic shared memory MIMD systems with snoopy caches saturate
rapidly.  However, this is simply the wrong approach to the problem.
SIMD architectures like the Connection Machine are scalable.  Perhaps
you did not study these.

>3) personally I feel parallel computing has no real future as the single cpu
>gets a 2-4 folds performance boost every few years, and parallel machines
>constructions just can't keep up with that. It seems to me that for at least 
>the next 10 years, non-parallel machines will still give the best performance 
>and the best performance/cost.

  This statement is not even true for MIMD processors.
Multiprocessor, with shared memory, used as file servers have _much_
better performance than comparable single processor systems.  Then
there are the issues of fault tolerance.  When a Multiprocessor fails,
you pull a board out and go on.  When a uni-processor fails, you wait
for field service.  Sequent is doing a booming business selling shared
memory multiprocessors.  Even DEC is selling a multiprocessor (the
VAXstation 3520).

                            Ian Kaplan
                            MasPar Computer Corp.
                            argosy!ian@decwrl.dec.com

  The opinions expressed here are not necessarily shared by MasPar
Computer Corp.