P4 dual core problem
 

I have a P4 D805 processor running at the normal 2.666GHz and get iteration times of 0.092sec if running only a single instance of prime95 (50% CPU utilization) but if I try running two instances of prime95 (with affinities set to different cores and 100% CPU utilization) the iteration times more than double to 0.199sec. The CPU-Z program doesn't show any CPU throttling and I have varied fan speeds to change my CPU temperature from 47C to 67C (monitored by MBM5) with no effect on single or double instance iteration times.
Does anyone have a similar experience or an explaination as to what is happening?

I had a D830 and have a D945. With both processors I had the same benchmark results running one instance of prime95 or two (one on each core obviously.)

Is it LL iteration times you speak of? If it is P-1 stage two or torture tests, you might not have enough memory and the OS would start swapping.

D8XX processors are quite sturdy, but I would try to keep the temperature under 65°C: thermal specifications from Intel is 64.1°C.

Check to make sure cpu affinity is set to '0' for one core, and '1' for the other core.

[QUOTE=rx7350;89883]Check to make sure cpu affinity is set to '0' for one core, and '1' for the other core.[/QUOTE]Or "Let program run on any CPU", although that will cause a performance hit on P4 platform.

More Info on problem
 

Yes it is the LL iterations and the memory usage of each instance is only ~23mb. Also, I do have the affinities set to "0" on one and "1" on the other instance but it makes no difference which I add as the 2nd instance so both cores are performing the same with one instance.
One other piece of info is that I have tried it both on XP-pro and Linux-64 Fedora and get very similar results. When using Linux I get a CPU throttling warning only if I try overclocking to ~3.1MHz and add the second instance. That's why I'm not overclocking when trying to run 2 instances.

Update - memory speed makes a big difference
 

I just swapped out my 266MHz DDR memory with a 333MHz DDR memory from another computer and this made a significant difference in iteration times. Single instance times went from 0.092sec to 0.085sec and double instance times went from 0.199sec to 0.131sec. It looks like memory speed makes a significant impact on interation speed, particularly with dual processors. I'm now going to look into upgrading to 533MHz DDR2 memory if I can find a good price.

Has anyone else noticed a difference with different memory speeds??