Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Dedicated Processors (was Sw vs. Hw BitBlit (CharBLT))
Message-ID: <1988Aug22.195431.7991@utzoo.uucp>
Organization: U of Toronto Zoology
References: <399@ma.diab.se> <76700044@p.cs.uiuc.edu> <1843@gofast.camcon.co.uk> <418@ma.diab.se> <374@augean.OZ>
Date: Mon, 22 Aug 88 19:54:31 GMT

In article <374@augean.OZ> idall@augean.OZ (Ian Dall) writes:
>... A multi CPU system is seriously complicated by the
>problems of avoiding a memory access bottleneck.

This is equally true of a multiple PU system.  Any system with multiple
processors that want to access memory a lot will run into this.  The
usual solution, for both balkanized and unified multiprocessor systems,
is to see to it that most of the memory accesses go to unshared memory of
some kind (cache, local memory, whatever) and shared resources are used
mostly when interprocessor communication is specifically wanted.
Balkanizing the processors -- dedicating some to specific jobs without
giving the software any say in the matter -- does not eliminate the
problem; what it does do is to make cruder and less useful solutions
look acceptable.

>To take an extreme case would you REALLY want to do without the micro
>in an ordinary dumb terminal and have the CPU do its work? Of course
>not! ...

Well, you know, there are 10^10 PCs out there with video boards that do
exactly that...

>... It is cheap and convenient to partition the system into
>chunks with a relatively slow (RS232) link between them.

Ah, but that's not the environment that the previous discussion has been
about.  Obviously, if communications are very slow then it makes sense to
have intelligence at both ends.  Preferably general-purpose intelligence;
an Atari ST or an AT&T 630 makes a much better terminal than an ordinary
dumb terminal, and it's not just because of the graphics.
-- 
Intel CPUs are not defective,  |     Henry Spencer at U of Toronto Zoology
they just act that way.        | uunet!attcan!utzoo!henry henry@zoo.toronto.edu