From: sjb5@ns1.cc.lehigh.edu (STACY JOHN BEHRENS)
Newsgroups: comp.os.os2.advocacy
Subject: Re: More Controversial Topics
Date: 15 Dec 92 16:36:09 GMT
Organization: Lehigh University

In article <1992Dec12.211305.22847@wam.umd.edu>, rsrodger@wam.umd.edu (Yamanari)
 writes:
>In article <Bz5yG0.Cqo@news.cso.uiuc.edu> walk@mrcnext.cso.uiuc.edu (Todd Walk)
 writes:
>>rsrodger@wam.umd.edu (Yamanari) writes:
>>>     It is my understanding, and this means that I'm draggin it out
>>>     of my memory, which is very poor these days, that this situation
>>>     really only occurs with some high number of processors--like
>>>     150 when you're talking about the Inmos T800 transputer.  However,
>>>     the last 20 or 30 processors add sufficiently little benefit
>>>     that it becomes almost pointless to add them.
>>
>>This will happen WAY before 150 or so processors on a SMP machine.  You've
>>got to remember that the processors share a main memory, so it's memory
>
>
>       You can buy T800 cards for the PC that have 4 processors.  Each
>       processor has 4 megs of memory *of it's own*.  In other words,
>       rethink your comment.
>
>>bandwidth that limits power and not the # of processors you can jam
>>onto a board.  About the most processors I've heard of on a SMP machine
>
>
>       What makes you think that all processors need go on one
>       board?  A backplane with a number of seperate CPU cards
>       would (and does) do nicely.


Terrific except that doesn't solve the bandwidth problem. The buses to
communicate between the various processor boards are almost certain to cause a
bottleneck.  You also need to worry about memory on various boards not
stepping on each other or if there is cenralized memory, processors not
steping in each other's way.  It isn't nearly as simply as popping a board
with a few processors on a passive backplane.

>
>>is 16.  Computers with more processors basically all use a distributed
>
>
>       I've heard of 32 for <$220,000 systems.  Then, of course,
>       there's things like a Connection Machine, the N-Cube,
>       supercomputers and so on.

Fine, how many of these are out there?  Furthermore do they need NT to run?
Machines like those are exedingly rare due to their price and those kind of
systems already have systems that work just fine right now.

>
>
>>memory setup (each processor has it's own main memory) and communicate
>>by sending messages to each other.
>
>
>       And?  You can feel free to assume that this was precisely
>       the machine I was describing.  The Inmos transputer has special
>       communicatiosn hardware (4 ?serial links/chip) for talking
>       one chip to another.
>
>       Does SMP *specifically* refer to machines that are not
>       distributed memory?

Special communications chips can work, but that is different from what you
were talking about before.

-- 
Stacy John Behrens
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The only justification for our concepts and systems of concepts is that they
serve to represent the complex of our experiences; beyond this they have not
legitimacy.                                  [Albert Einstein]
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Newsgroups: comp.os.os2.advocacy