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Prime95 icon in its "on" state
Prime95 icon in its "on" state
Prime95 26.5 running on a Windows 7 system
Prime95 26.5 running on a Windows 7 system
Developer(s)George Woltman
Initial release3 January 1996; 24 years ago (1996-01-03)
Stable release
29.8 build 6 / August 18, 2019 (2019-08-18)[1]
Written inASM, C
Operating systemMicrosoft Windows, macOS, Linux, FreeBSD
TypeMersenne prime finder / system stability tester
LicenseFreeware[2] Edit this on Wikidata

Prime95, also distributed as a command-line utility mprime under FreeBSD and Linux, is a freeware application written by George Woltman. It is used by Great Internet Mersenne Prime Search (GIMPS), a distributed computing project dedicated to Mersenne prime hunting. In overclocking circles, it is commonly used for stability testing.[citation needed]

Although most[3] of its source code is available, Prime95 does not qualify as free and open-source software because its end-user license agreement[2] states that in the event that the software is used to find a record prime that qualifies for the bounties offered by the Electronic Frontier Foundation,[4] any prize money is to be claimed and redistributed by GIMPS.

Finding Mersenne primes by distributed computing[edit]

Since the foundation of GIMPS in 1996, 17 new Mersenne primes have been found by participants of the project.[5]

To accomplish this, the program implements the following algorithms:

Due to the large volume of candidates and the scarcity of Mersenne primes, the program also implements some computationally cheaper tests to quickly exclude composite candidates:

Use for stress testing[edit]

Prime95 28.7 running a stress test on an Intel quad-core Windows 10 system

Due to the operations performed by Prime95 and its emphasis on performance, extreme pressure is exerted on the various computer subsystems when used with certain parameters. This can help identify issues with RAM, FPUs and power delivery and other components. In a stable system, running Prime95 would not result in crashes or incorrect results. It is due to this that Prime95 is one of the most common tools used by the overclocking community to assess the stability of their systems.[6]

See also[edit]


  1. ^ Woltman, George. "FYI: 29.8 is now the official download version at". Retrieved 2019-05-07.
  2. ^ Woltman, George. "The security code or checksum is hard to forge. This is the only source code that is not published".
  3. ^ "EFF Cooperative Computing Awards". Electronic Frontier Foundation. 2008-02-29. Retrieved 2019-05-08.
  4. ^ "GIMPS History - PrimeNet". Great Internet Mersenne Prime Search. Retrieved 2019-05-09.
  5. ^ "How To Run a CPU Stress Test Using Prime95". 2015-12-10. Retrieved 2019-05-23.

External links[edit]