> When two or more processors come into play, what is the increase rate of
> processing over a single processor? Is does it works out as 100% increase
> over that of a single processor or is it limited by other factors such as
> caching, disk i/o or whatever?
>
> I'm guessing it's a 100% increase.
Not a chance. Communication overhead, cache coherency issues,
contention issues, &c &c &c will *always* bring the increase down,
sometimes a long way down.
The worst such decrease that I've heard of recently was for a
particular 64-processor distributed simulation which ended up running
at 0.83 times ths speed it would have run on a single processor. And
I'm sure that there are worse examples out there - all you need to do
is look for simple-minded concurrent communication algorithms and
you'll find more :(
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