On 18 Jul 00, at 18:45, Nasser, David wrote:

> Oooops. In a post yesterday, this po' fella said:
>
> >"There are a mere handful of multi-threaded applications
> > (i.e. CAD) capable of using dual Intel cpu's. If you run
> > garden-variety PC applications (i.e. Microsofty Word, Excel, etc)
> > on, say, a dual 500 mhz system, you can expect to get something
> > like the throughput associated with a single 500 mhz cpu system."
>
> It should have been phrased:
>
> "If you run a single garden-variety PC application ..." you utilize
> only one cpu.
>
> This is owing to the fact that, if you have a proper SMP OS
> and you run multiple applications, you can expect to utilize
> both processors as each app. is separately threaded.
>
> Apologies for the misleading wording.
>
>   David

  I disagree.

  At one point, I took a look at the Task Manager display on my NT
4.0 Workstation, and found that by the time that Windows was up and
running and ready for me to launch foreground applications, there
were about 40 (!) threads sharing CPU time.
  Now, if I had been running that same software load on my dual-CPU
box, on average half of those threads would be scheduled on one CPU
and half on the other.  In the extreme case, a single piggish
application might have had one CPU to itself with everything else
going to the other, but even in that case I would see improvement
over the single-CPU case.
  [In fact I have seen this; a piggish application that brings a
single-CPU NT box to its knees, but when the same app runs on my dual-
CPU box, the GUI and friendlier apps remain briskly responsive.]

  The fact that a single non-multithreaded application will only run
on one CPU at a time is irrelevant; I don't think there's an OS that
supports dual CPUs on which you can get to a state where there's only
a single thread running, except during boot and shutdown procedures.
The rest of the time, there are always multiple threads, and whether
any of them share a single application instance doesn't matter to
overall system performance.

David G

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