Path: utzoo!attcan2!uunet!husc6!bbn!gatech!hubcap!Chris
From: alberta!cdshaw@UCBVAX.BERKELEY.EDU (Chris Shaw)
Newsgroups: comp.parallel
Subject: Re: parallel numerical algorithms
Message-ID: <1796@hubcap.UUCP>
Date: 1 Jun 88 20:26:50 GMT
Sender: fpst@hubcap.UUCP
Lines: 25
Approved: parallel@hubcap.clemson.edu

>In article <1691@hubcap.UUCP> you write:
>>Anyone care to try for a strict definition?

I think that the best way to think of pipelined parallelism under the Flynn
taxonomy is to call it MISD. In other words, the "unused" classification
among SISD, MISD, SIMD, MIMD does actually contain examples of real machines.

I suppose the real difficulty is with definitions: What is an instruction?
What is data? What is a CPU?

If "instruction" in the Flynn taxonomy means "operate on a data item by passing
it from one register through some combinatorial circuit to another register",
then the above classification of pipelines as MISD machines makes sense.

Of course, assuming that the four Flynn classes are orthogonal is probably a 
mistake. They can probably best be thought as subsets, where SISD is a subset
of MISD, which is a subset of SIMD, which is a subset of MIMD. At the highest
level, a Cray X-MP may be MIMD, but each cpu is MISD, while the scalar part of 
the CPU is SISD.

But all this relies on well-defined notions of data, instruction, etc.
-- 
Chris Shaw    cdshaw@alberta.UUCP (via watmath, ihnp4 or ubc-vision)
University of Alberta
CatchPhrase: Bogus as HELL !