Geoff Canyon wrote:
> Just to make sure I understand correctly: The OS gives Word 100,000
> cycles. If Word yields after only 20,000 cycles because it's just
> sitting there waiting for the next keypress, the OS continues to
> give Word 100,000 cycles each time around, rather than try to
> accurately predict what Word will need based on past data. If, on
> the other hand, QuickTime uses every one of those 100,000 cycles
> productively making a movie look good, then the OS considers it
> greedy and the next time around gives it only 50,000? How does
> that make sense?
I believe Unix does the same thing, which is why Unix is not a "real
time" OS. Its a design from the Good Old Days where there was basically
nothing you could do on a computer that was so time critical that a
process would need every last cycle allotted to it. I suppose the idea
is, any process that does use every cycle allotted is either buggy or
just rude.
Or even dangerous - nasty processes could keep yelling for more and more
cycles until they drag the computer to a complete stop. That's bad
enough when you're working on a single-user PC, but if you are on a
multi-user system with 1000 users scattered all over the country, that
is bad with a capital B.
The Unix/NT model is a good system for most things you want to do, but
not the best for time critical applications like animation or (say)
controlling a nuclear reactor.
> One thing that always impresses me about demos of the BeOS is the
> way the multitasking is handled. I don't know the underlying
> methodology
Among other reasons, BeOS is designed from the ground up to be fully
multi-threaded, multi-processor, and all the other multi- buzzwords you
might care to use.
My understanding is that every single process, from the kernal to the
application layer, runs as an independant thread. I'm not sure if this
includes drivers. But however they do it, BeBoxen are responsive, even
when doing ten things at once.
--
Steven D'Aprano
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