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Prime95 - Stress Test Your CPU

information   Information

is a freeware program originally designed to find new Mersenne prime numbers. Given the nature of Prime95 it is now widely used as a CPU stress testing utility to gauge the stability of a CPU, especially when overclocking a system. It includes a Torture Test designed specifically to test PC subsystems for errors.

Prime95's stress test feature can be configured to test various system components by changing the FFT size. There are three pre-set configurations available:

  • Small FFTs (Primarily tests FPU and CPU caches)
  • In-Place FFTs (Maximum power consumption; tests FPU and CPU caches, some RAM)
  • Blend (Tests everything including RAM)

On a completely stable system Prime95 will run indefinitely. If an error occurs the stress test will terminate indicating the system may be unstable.

warning   Warning

While running Prime95 your CPU will become incredibly hot, it is imperative that you keep a constant watch of your CPU temperature with a system monitoring utility such as Speccy, Speedfan or HWMonitor. If your CPU temperature does reach dangerous levels stop the Prime95 stress test to prevent inflicting damage on your CPU.

Note   Note

Run Prime95 for up to three hours, unless errors occur sooner. Depending on temperatures feel fee to run the test for longer to thoroughly test overclock or system stability

Here's how:

1: Download the relevant version of Prime95 for your system.

2: Extract the zipped folder.

3: Open the extracted folder and click on the prime95.exe.

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When Prime95 launches click on the Just Stress Testing button.

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5: Select Small FFTs (or whichever specific test you've been asked to perform if different). Click OK to start the test.

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6: A Worker thread will open for each Logical CPU, these threads will update information about every Logical CPU being tested.

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information   Information
If one or more threads fail the Worker/s will stop and you will see the following message in the relevant thread/s
FATAL ERROR: Rounding was 0.XXXX, expected less than 0.XXXX
Hardware failure detected, consult stress.txt file

7: To stop the test at any time click on Test then Stop... from the resulting context menu.

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8: If the test runs without detecting any errors the results will look similar to the results shown in the screenshot below.

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That's it,