Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: dedicated vs general-purpose CPUs
Message-ID: <1988Aug3.180947.12070@utzoo.uucp>
Organization: U of Toronto Zoology
References: <5254@june.cs.washington.edu> <76700032@p.cs.uiuc.edu> <1988Jul28.170834.6949@utzoo.uucp> <2379@sugar.uu.net>
Date: Wed, 3 Aug 88 18:09:47 GMT

In article <2379@sugar.uu.net> karl@sugar.uu.net (Karl Lehenbauer) writes:
>I don't know at what point this becomes weirding out...

I'm not quite sure myself, but I suspect that the borderline is farther
to the weird side than most people think.  Sometime I may have a try at
proving this.

>Isn't it OK to have a
>dedicated processor on the multiport serial I/O boards? ...

If you're expecting long interrupt latency or some other such problem on
the main processor(s), then sure it's okay.  Otherwise, why bother?  The
non-smart serial ports on a Sun 3 are faster than the ALM-1 "smart" multiport
board, even with the slow interrupt handling of a 68020.  Granted, this is
an extreme example; the ALM-1 is pretty old.  But phrase it another way:
do you want your CPU power in one block that you can allocate as you please,
or divided up into fixed-size chunks, most of which are not under your
control?  If allocating it yourself doesn't impose excessive overhead or
latency problems, clearly the former is preferable.

>... Why can't we put a processor anywhere that's useful
>and have general multiprocessing as well?

Because processors cost money and have to be programmed, and one would
prefer to get maximum use out of the former while minimizing the complexity
of the latter.

>Why should my graphics CPU, with
>dedicated memory and, eventually, parallel processing, hardware transforms
>and such have to be complicated by the need to run user programs?

Why should user programs be denied the use of parallel processing, transform
hardware, and such?  Do you really think there's only one use for that
equipment?
-- 
MSDOS is not dead, it just     |     Henry Spencer at U of Toronto Zoology
smells that way.               | uunet!mnetor!utzoo!henry henry@zoo.toronto.edu