Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!apple!malcolm
From: malcolm@Apple.COM (Malcolm Slaney)
Newsgroups: comp.arch
Subject: Re: Barrel processors & string ops [really: Don't look back...]
Message-ID: <26262@apple.Apple.COM>
Date: 23 Feb 89 17:02:18 GMT
References: <747@atanasoff.cs.iastate.edu> <28200275@mcdurb> <4290@pt.cs.cmu.edu> <13582@winchester.mips.COM> <24582@amdcad.AMD.COM>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 22

In article <24582@amdcad.AMD.COM> rpw3@amdcad.UUCP (Rob Warnock) writes:
>As John Mashey says, with current chip technology, barrel processors don't
>seem to make much sense. 

Maybe I missed something in the definition of a barrel processor but isn't
the new Stellar machine a barrel processor much like the HEP?  I just read
the machine overview last night and they have four "virtual" pipelines that
time share a single long pipeline.  I wonder what it is about the Stellar
architecture that makes them think they can succeed where Burton Smith (HEP)
couldn't?  Is it just the graphics?

This is one of the advantages they claim:
	At any particular moment, 12 instructions are active in the pipeline,
	but each stream (of four) has only three instructions active.  In this
	way, the architecture can achieve the performance of a deep (12 stage,
	50 nsec) pipeline, while experiencing the minimal "pipeline drain"
	cost of a shallow (3 stage, 200 nsec) pipeline.
I don't have to pay for the machine so I can't comment on its price. I did
recompile my ear models on the machine and they worked without changes and
ran much faster than a Sun...but not as fast as the code on our Cray XMP.

								Malcolm