Path: utzoo!mnetor!uunet!husc6!hao!ames!amelia!orville.nas.nasa.gov!fouts
From: fouts@orville.nas.nasa.gov (Marty Fouts)
Newsgroups: comp.arch
Subject: Re: Single/Multi Tasking position summary (was Re: Single tasking)
Message-ID: <83@amelia.nas.nasa.gov>
Date: 4 Jan 88 17:45:04 GMT
References: <60@amelia.nas.nasa.gov> <2428@encore.UUCP>
Sender: news@amelia.nas.nasa.gov
Reply-To: fouts@orville.nas.nasa.gov (Marty Fouts)
Organization: NASA Ames Research Center, Moffett Field, CA
Lines: 42

In article <2428@encore.UUCP> collins@encore.UUCP (Jeff Collins) writes:
>
>In article <60@amelia.nas.nasa.gov> fouts@orville.nas.nasa.gov (Marty Fouts) writes:
>>...  This exchange of ancedotal evidence leads to the hard question:
>>For which problems will a parallel processor using the best available
>>implementation technology give better cost/performance than the best
>>single processor?
>
>	Vector processors are a special form of parallel processors (this 
>	should start lots of flames).  Perhaps the Convex is simply implemented
>	better than the Alliant?  You are using one comparison to condemn
>	an entire class of machines.
>

Please don't put inflamatory words in my mouth.  I cited one example
to show that sometimes one class of machines can outperfom the other
and asked under what circumstances this is true.  I never condemned
either class of architectures.  (At best a cynical reading of what I
said would claim that I condemned the Alliant implementation, and I
didn't even do that.)

To clarify my original question:

As an architect, I would like to know:

For which problems will a parallel processor using the best available
implementation technology give better cost/performance than the best
single processor?

This question is really asking if there are any inherent limitiations
due to either implementation technology or architectural constraints
which lead to one or the other class of architectures being stronger
for a particular class of problem.

As a user, I would like to know:

For which problems will parallel processor X give better
cost/performance than single processor Y?

In this case, I don't care why the relationship holds, only that it
holds, and how effectively I can predict it.  (So I can best take
advantage.)