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Why does Prime95 go to 75% load?

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  • CPUs
  • Overclocking
Last response: in Overclocking
February 27, 2010 3:25:15 AM

Hello,

I'm new to over clocking and am currently trying to get my 920 D0 working at 4.2 Ghz, I know my CPU Voltage is still a little two low (1.275) because it will crash prime 95 after 20-30 min, the thing i find kind of odd is that after about a couple minuets the cpu load goes from 100% to 75% but my temperature never goes above 55-57 degrees (according to real temp 3.4 and core temp 0.99.5) and nothing on CPU-Z changes (multiplier, bus speed core volt). My question is, what is telling my computer to throttle down to 75%? is it prime 95? I'm assuming there is something that knows that there is insufficient voltage?

Thank in advance!

Mike

More about : prime95 load

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a b K Overclocking
February 27, 2010 8:59:38 AM

Uh, did you check the worker threads of prime95? One of them might have return a "FATAL ERROR" or something similar. The moment a thread fails, it halts execution. So if one of your CPU cores went bad with the calculations, the thread stops. If you have 4 cores, and one of them stop being used, you would have 75% load (3 out of 4 cores at 100, the last one 0). Do you have hyper threading on? That would give you 8 logical cores. Two or three cores failing would give you 70-80% usage.
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a b K Overclocking
February 27, 2010 2:03:09 PM

Yea, good poiint by gracefully. I've never seen Prime95 to not force every available core to run full 100% unless of course that core is failing or has already failed.

Check your Prime95 window and make sure all worker cores are still running.
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February 27, 2010 2:49:53 PM

Best answer selected by dutchmichael82.
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February 27, 2010 2:53:54 PM

Ya that was what it was, I didn't realize that if there was an error that it would just shut down one of the cores (though it makes perfect sense). And I do have hyper threading off. I upped the voltage a bit and it's been running stable for the last 2 hours. Thanks for your help guys!
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a b K Overclocking
a b à CPUs
February 28, 2010 6:09:05 PM

What do you do with this system? I would either up voltage or lower the clock a tad bit and enable HT.
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