Does your CPU have hyper-threading for sure, and it's enabled in the BIOS?

Task Manager will show one graph per CPU... If you only see a single graph,
your OS only thinks it has one CPU (counting all virtual and all real CPUs).

I also assume you're using WinNT/Win2k/WinXP since Win98/ME doesn't support
multiple CPU's (and doesn't really have Task Manager either...just that
system resources thing).

Check your list of running processes and see how many Prime95's show up.
Should just be 1.  If you have 2 running, yeah, running 2 processes on a
single CPU, even with the multi-threading, will generally hamper how well
either one runs.

I once toyed with the idea of running LL tests on the real CPU and running
factoring tests on the virtual one, but I never could decide if that was
helping out at all...My gut tells me no just because of the memory accesses
and not using the single L1/L2 caches on the CPU as well as they could be.

By the way, that's a sight to behold when you have a quad CPU P4 system... 8
graphs happily bouncing away.  I'm sure on an 8 CPU system it must be
terribly impressive to have 16 graphs showing up, but I've yet to get my
hands on such a system. :) 

>   I have a Pentium 4 processsor and TM indicates an average 
> usage of close to 100% CPU for Prime 95 - am I running 
> 'multiple instances' without being aware of it? If so, how do 
> I prevent this if it will degrade efficiency?

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