Have you ever heard something like "The NB is stressed the most during 512K FFTs. This happens about 2-3 hours into Blend"? Or, have you ever had Prime95 consistently fail on the same FFT size? Well, that's when the custom test comes in handy.
We all know about the three pre-set modes available for Prime95: Small FFTs, In-Place FFTs, and Blend. Small and In-Place modes test the FPU and caches. Blend mode tests everything, including RAM.
By selecting Custom, you have total control over which FFT size/s are run. In general, the smaller FFTs stress the CPU, while the larger FFTs stress the memory and chipset - with one exception, the "in place" FFT.
What is an "in-place" FFT?
An "in place" FFT is simply an FFT that is calculated entirely inside its original sample memory. In other words, calculating an "in place" FFT does not require additional buffer memory. - Source(#2.3)
Ok, so between the definition above and the fact that Prime95 labels the "In-place large FFTs" test as max heat, power, and some RAM tested. We know that when the FFTs are "in place", the RAM and chipset aren't being tested all that hard, regardless of the FFT size.
Below are a few screen shots of different custom tests.
RAM & Chipset Test
Note: when not using the "in place" option, be careful not to set the "memory to use" too high. If it's set too high, the system will start to use the paging file which will not stress the RAM.
Oh noes...it's always failing at 512 FFT size and I don't want to wait two hours for blend to reach that test
or you could do something like this
Maybe this is common knowledge to most here? If not, this should give you a general idea of what to do.
Edited by tmunn - 10/15/12 at 7:25pm