Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!gatech!hubcap!mcvax!cernvax!hjm
From: mcvax!cernvax!hjm@uunet.UU.NET (Hubert Matthews)
Newsgroups: comp.parallel
Subject: One parallel v. many uniprocessor algorithms
Summary: Don't forget the cost of the system...
Message-ID: <5374@hubcap.clemson.edu>
Date: 2 May 89 18:03:11 GMT
Sender: fpst@hubcap.clemson.edu
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Approved: parallel@hubcap.clemson.edu

One of the things that I didn't see mentioned (perhaps someone said it
and I missed it) regarding the Distributed Simulation discussion about
whether it is "better" to run several simulations in parallel or have
one algorithm spread over several processors is the subject of memory
requirements, or roughly translated: cost.

Consider n processors running n copies of the same program.  The total
memory requirement will be n times the uniprocessor requirement.  Now
consider the case of one program distributed over n processors.  Let's
make a wild guess and say that the total memory in the distributed
version is of the same order of magnitude as the uniprocessor version;
the exact figure is not important.  For the uniprocessor version, we
need n times as much memory to do the same work in the same time, so
we lose out on the cost of the extra memory, and since the cost of
memory is the dominant cost in a computing system today, this does
seem to give you less bang-per-buck.



-- 

	Hubert Matthews