Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-lcc!ames!killer!elg
From: elg@killer.DALLAS.TX.US (Eric Green)
Newsgroups: comp.arch
Subject: Re: dedicated vs general-purpose CPUs
Message-ID: <5145@killer.DALLAS.TX.US>
Date: 9 Aug 88 05:17:21 GMT
References: <5254@june.cs.washington.edu> <76700032@p.cs.uiuc.edu> <1988Aug3.180947.12070@utzoo.uucp> <1221@ficc.UUCP> <1988Aug7.013952.7842@utzoo.uucp>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 38

In message <1988Aug7.013952.7842@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) says:
>In article <1221@ficc.UUCP> peter@ficc.UUCP (Peter da Silva) writes:
>>So, you *have* to use fixed size blocks. Once you have pulled all the
>>power you can out of your 680x0 or RISC chip, and you need more MIPS,
>>you have to add more processors.  So, you have the graphics (and serial-IO
>>and disk IO and any other IO you care to name) wheel of life.
>>The other alternative is to build your own custom [processor]...
>
>You forgot the third alternative:  add a second (third, etc.) 680x0 or
>RISC or whatever.  That adds to your pool of centrally-managed power,
>rather than balkanizing it as specialized auxiliary processors do.  A
>multiprocessor system isn't quite as good as one fast processor, but with
>competent designers it can come close.

One problem with that is cost. It takes a lot of "glue" to build a
multiprocessor, whereas the central-CPU/smart-peripheral interface
only requires a DMA protocol of some sort, which most computers will
have already. I'm not quite sure how much a 68030 costs. But I just
read a brief product announcement of a new 32-bit TI video chip that
will cost $95 or so in quantity, for most of the logic needed for a
video display, plus blitting etc.... I doubt that you could add
another 68030 for that price, especially considering the "glue" etc.
Of course the dual-68030 system would be more powerful. But when
you're building a low-end workstation, you have to shave dollars and
cents wherever you can find them, while still meeting minimum
performance standards... else, you find your market share quickly
eroding. 

I love raw CPU power as much as the other guy. But, general-purpose
multiprocessing and "cheap" do not fit in the same sentence
(especially when you get finished paying the development costs of a
multiprocessor OS kernal & appropriate modifications to the rest of
the system -- software is not free, tho EEs would like to think so
;-).

--
Eric Lee Green    ..!{ames,decwrl,mit-eddie,osu-cis}!killer!elg
          Snail Mail P.O. Box 92191 Lafayette, LA 70509              
       MISFORTUNE, n. The kind of fortune that never misses.