> >
> > "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.

Sharing cpu time? Or just sharing memory??

I boot my little NT desktop, let it settle down, and load Task
Mngr. It shows maybe 40 threads. I click the "Performance" tab,
and it indicates that the 40 threads are consuming 0-1% of cpu
usage.

>   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.

You would indeed, if the other threads were doing something
that consumed cpu cycles. And, of course, this is possible.
But I've found it to be the exception rather than the rule
in the world of desktop computing usage.

>   [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.]

This is possible under certain circumstances.

>   The fact that a single non-multithreaded application will only run
> on one CPU at a time is irrelevant;

I disagree.

> 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.

Right now my little NT desktop at work has loaded, in addition to the
40 threads previously mentioned:

  Idiot Outlook
  3270 emulator
  Internet Explorer instance 1
  Internet Explorer instance 2
  Netscape Navigator
  UltraEdit

But I'm only using UltraEdit to compose this message. Task Manager
sez 4% cpu usage (on a single PII 400 mhz desktop). Theres no
cpu load to distribute because all the threads save this
one are not using material cpu cycles. And this one isn't
using much.

It is a "personal computer". The "person" using it may
have Lord-Knows-What-All loaded in memory, but he/she
_typically_ is concentrating on a single task, and usually
this does not cause multiple applications in memory to consume
a material number of cpu cycles.

"Garden-variety PC applications are almost ALWAYS i/o bound".
Very seldom are they compute-bound. Some specialized PC
applications _do_ tend to be compute-bound.

I guess my advice to folks considering a dual-cpu system is
as follows:

a) If you have a highly specialized fully multi-threaded
   compute-bound-type application (i.e. AutoCad) that you need to
   run intensely, day-in and day-out, then look into a dual system
   running an appropriate OS.

b) Otherwise, get a good solid single cpu system and
   consider using the extra $ you would need for a dual
   system for more sophisticated/faster i/o subsystem(s).

c) If you spend most of your time running word proc'g
   and/or spreadsheet, just get a good solid single cpu system
   and pocket any extra $ that you might have spent on
   an extra cpu or <whatever>.

All of the above is solely based on computer architecture
and computer usage. It totally ignores  "status" and
"bragging rights" and other things that might be
associated with a dual cpu system.

Hope this helps somebody, somewhere ...

  David N.

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** David Nasser                     **     [log in to unmask]    **
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