Prime 95 32-Bit vs 64-Bit

Spook161 · September 29, 2019

So, I was trying to test RAM with Prime-95, as it happened, I was using 32-Bit Prime. Well, I found the memory limitations using Prime95 32-bit, so I downloaded the 64-bit, and started using that. Then I backtracked, and attempted some CPU tests using the 64-bit. What I noticed is that P95 isn't staying within the Small FFT parameters defined, either through the small FFT setting OR the manual setting. The 64Bit would start with a 384k Test, and consequently the CPU temperatures would be much lower than would be expected. I'm choosing Smallest FFT's, which should be between 4k and 24k FFT size (according to the settings), and its starting with :

Test 1, 44000 Lucas-Lehmer in-place iterations of M7471105 using FMA3 FFT length 384K, Pass1=384, Pass2=1K, clm=4.

32Bit works fine, and starts with a 4k FFT, and runs a good 8 degrees hotter :

Test 1, 7000000 Lucas-Lehmer in-place iterations of M83839 using FFT length 4K.

I am using the latest version of Prime95 for testing, 29.8b6 and have turned off AVX, apparently at some point they have FINALLY added an AVX disable checkbox.

Does anyone else observe this behavior? is it normal? I've been doing some searches, but my google-fu is failing me.

Falkentyne · September 29, 2019

Post this in the software section of their forum in the prime thread there. I doubt anyone on LTT can help you.

Spook161 · September 29, 2019

Well, I was able to figure out my problem. As many things it was multilayered. The first problem was that I updated to Win10 1903, which change the permissions on my "Program Files" folder, which is where my Prime95 folder resided. So, Prime95 was not able to write any files in the folder anymore, and it apparently is required to change from the default parameters, ie run small FFT's in this case. Once I moved the folders under my documents folder, Prime could write the files, and now I am able to run the small FFT's just fine under the 64-bit version.

Makes me wonder how the 32-bit version was different in that regard, as it was under "Program Files" as well. Everything working fine now.

Thanks for the look.