Prime95 has become extremely popular among PC enthusiasts and overclockers as a stability testing utility. It includes a "Torture Test" mode designed specifically for testing PC subsystems for errors in order to help ensure the correct operation of Prime95 on that system, which effectively stress-tests a PC.
The stress-test in Prime can be configured to better test various components of the computer by changing the fast fourier transform (FFT) size. Three pre-set configurations are available: Small FFTs, In-Place FFTs, and Blend. Small and In-Place modes primarily test the FPU and the caches of the CPU, whereas the Blend mode tests everything, including the memory.
By selecting Custom, the user can gain further control of the configuration. For example, by selecting 8-8KB as the FFT size, the program stresses primarily the CPU. By selecting 2048-4096KB and unchecking the "Run FFTs in-place" checkbox, providing the maximum amount of RAM free in the system, the program tests the memory and the chipset. If the amount of memory to use option is set too high then system will start using the paging file and the test will not stress the memory.
On an absolutely stable system, Prime95 would run indefinitely. If an error occurs (the tray icon will become yellow from the default red, indicating that the test has halted), there is a chance that the system is unstable. There is an ongoing debate about terms "stable" and "Prime-stable", as Prime95 often fails before the system becomes unstable or crashes in any other application.
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