Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!udel!rochester!pt.cs.cmu.edu!klingon.pc.cs.cmu.edu!sc
From: sc@klingon.pc.cs.cmu.edu (Siddhartha Chatterjee)
Newsgroups: comp.arch
Subject: Re: Shared Memory vs. Distributed Systems
Keywords: Shared, distributed, message
Message-ID: <6708@pt.cs.cmu.edu>
Date: 26 Oct 89 20:15:43 GMT
References: <20764@usc.edu> <1646@ncrcce.StPaul.NCR.COM> <9605@june.cs.washington.edu>
Organization: Carnegie-Mellon University, CS/RI
Lines: 17

In article <9605@june.cs.washington.edu> rik@cs.washington.edu (Rik Littlefield) writes:
>Perhaps a more fundamental difference is that shared memory machines
>provide hardware to guarantee that all processors have a consistent view of
>memory.  Cooperation between processors can be controlled just by

Well, yes and no.  On a bus-connected machine like the Encore you have
snoopy caches that keep the data consistent and KEEP IT CLOSE TO THE
PROCESSOR.  On something like a Butterfly, the default behaviour is that
shared data is not cached; so yes, memory is consistent, but you have to go
out across the network to access it.  You can do explicit cache flushing in
software, but that's a different game.

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ARPA:	Siddhartha.Chatterjee@CS.CMU.EDU
USPS:	School of Computer Science, CMU, Pittsburgh, PA 15213
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