Prime95 is a free program that is used to test the stability and performance of a computer's processor.

It was written by George Waltman and is an official client of the GIMPS (Great Internet Mersenne Prime Search) project, which searches for Mersenne prime numbers.

The program works as follows: it generates random numbers that are candidates for Mersenne prime numbers and checks them for simplicity using the Lucas-Lemaire algorithm. This algorithm requires a large number of floating point calculations that load the processor to the maximum. If the program detects an error in the computation or a discrepancy with the expected result, it means that the processor is unstable or has a defect. If the program runs without errors for a long time, it means that the processor is stable and can handle a high load.

The program also has other operating modes such as FFT (Fast Fourier Transform) test, mixed load test or Mersenne test. These modes allow you to test different aspects of the processor such as cache, memory or bus. The program also allows you to configure different test parameters such as FFT size, run time, number of threads, etc.

The Prime95 program is widely used by people who overclock computers or system administrators who want to check the reliability of their servers. The program also helps in finding new Mersenne prime numbers, which are important objects of study in mathematics and cryptography. So far, 51 Mersenne prime numbers have been found, the most recent of which was discovered in 2018 using the Prime95 program.