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From: dave@ur-helheim.UUCP (David F. Carlson)
Newsgroups: net.arch
Subject: Re: Are "discrete" CPUs faster than VLSI?  And why?
Message-ID: <408@ur-helheim.UUCP>
Date: Tue, 26-Nov-85 11:59:36 EST
Article-I.D.: ur-helhe.408
Posted: Tue Nov 26 11:59:36 1985
Date-Received: Fri, 29-Nov-85 21:30:12 EST
References: <1795@peora.UUCP> <277@l5.uucp>
Reply-To: dave@helheim.UUCP (David F. Carlson)
Organization: U. of Rochester, EE Dept.
Lines: 40

In article <277@l5.uucp> gnu@l5.uucp (John Gilmore) writes:
>In article <1795@peora.UUCP>, jer@peora.UUCP (J. Eric Roskos) writes:
>> More generally, ...CPUs built with discrete
>> components (as vs. all on a single IC) tend to be faster. 
>
>I think the reasons are complexity and generality.  VLSI chips can only
>handle so much complexity -- once you exceed the number of gates you can
>fit, you have to go to a board-level design.  This was the constraint
>on Vax-on-a-chip for a number of years.  This is especially true in very
>fast logic families like ECL.
>
> blah blah blah blah blah blah blah blah blah blah blah blah blah blah 
>That's why discrete CPUs are faster than VLSI CPUs.  :-)


It seems to me that the very "discrete" CPU designs which your boast are faster
here are constructed of VLSI components.  The bitslice and large gate arrays
which are essential to the "modern" "discrete" realization have more complexity
on them that those silly 8 bit machines we all confess to have designed/played
with in the 70's.

Comparisons involving ECL bitslice and NMOS VLSI will get an apples and oranges
response from me.  ECL is electrically very different that NMOS.  Were I to 
design a 68000 on a chip using ECL I could heat a several homes before the devices
melted into slag silicon.  Fabrication and packaging complexity limit ECL VLSI
more than an inherant "complexity" limit.  

Now, look at the 68020 vs. (custom) VAX 750's CPUs in the dhrystone benchmarks.  The
architectures are similar (bulkwise:  registers, memory management, intruction
types, etc.)  When a Clipper system is built (although this is a chip set :-) 
another clean strike for VLSI will be struck.  I welcome this debate.  Any takers??


-- 
"The Faster I Go the Behinder I Get"
--Lewis Carroll

Dave Carlson

{allegra,seismo,decvax}!rochester!ur-valhalla!dave