Prime95

Prime95

Prime95 28.7 running on an Intel quad-core Windows 10 system
Developer(s)	George Woltman
Stable release	28.9 / March 29, 2016 (2016-03-29)
Operating system	Microsoft Windows, macOS, Linux (MPrime), FreeBSD (MPrime)
Type	Mersenne prime finder / system stability tester
License	GIMPS prize terms
Website	mersenne.org

Prime95 is the freeware application written by George Woltman that is used by GIMPS, a distributed computing project dedicated to finding new Mersenne prime numbers. More specifically, Prime95 refers to the Windows and macOS versions of the software.

MPrime is the Linux command-line interface version of Prime95, to be run in a text terminal or in a terminal emulator window as a remote shell client. It is identical to Prime95 in functionality, except it lacks a graphical user interface.

Although most of the GIMPS software's source code is publicly available, it is technically not free software as users must abide by the project's distribution terms if the software is used to discover a prime number with at least 100,000,000 decimal digits and wins the $150,000 bounty offered by the EFF. As such, a user who uses Prime95 to discover a qualifying prime number would not be able to claim the prize directly ($50,000 will go to the person who finds the prime number, $50,000 will go to a mathematics-related charity, $50,000 will be kept as reserve by GIMP). A free software package would not have this restriction.

The code that is used to generate checksums is not publicly available for security reasons. The rewritten FFT assembly code in the current stable version 28 (since June 1, 2014) uses FMA instruction set (FMA3) instructions of Haswell (microarchitecture) CPUs (Core i3/i5/i7-4xxx models), resulting in a huge performance increase.