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Prime95

Prime95 is free software for searching for Mersenne primes and contributing computing work to GIMPS, an international public project.

Place
#11 of 26
Score
6.2
Prime95's website

What Prime95 is

Prime95 is free software for searching for Mersenne primes and contributing computing work to GIMPS, an international public project. It can also put a sustained, heavy workload across CPU cores to check the stability of a processor and its L1, L2, and L3 caches. For project work, the program contacts PrimeNet to receive assignments; users can see computer progress and manage work remotely through the account’s CPUs page. Listed tasks include PRP and Lucas-Lehmer tests, P-1 and ECM factoring, and trial factoring. Downloads are listed for Windows, Linux, Mac OS X command-line, and FreeBSD. Administrators can use a GUI-less Windows service build, which is intended for Windows Server experts. The source archive covers Windows, Linux, FreeBSD, and Mac OS X, though its code is described as non-portable. Version 30.3 introduced a Resource Limits dialog for controlling usage. Recent NVIDIA or AMD discrete GPUs may be more powerful than CPUs for prime testing or factoring, with separate GPU programs communicating with PrimeNet through AutoPrimeNet.

Good

  • Free to use indefinitely on authorized computers.
  • Can test CPU and L1/L2/L3 cache stability.
  • PrimeNet supports progress viewing and remote work assignment control.
  • Resource Limits dialog controls resource usage.

Watch out

  • The Windows service build is intended for Windows Server experts.
  • Source code is described as non-portable.
  • Software and information are provided without warranty.

Who it suits

Prime95 suits people who want to contribute computer work to GIMPS or run a consistent CPU workload to check processor and cache stability. The GUI-less Windows service build is intended for Windows Server experts.

Verdict

Prime95 serves both Mersenne prime project work and sustained CPU stability checks, with versions listed for several operating systems. Its service build is aimed at Windows Server experts, and its license provides no warranty.

Plans and prices

From Prime95's own pricing page, checked 7 Oct 2026.

All about pricing
PlanPriceWhat it gives you
Prime95FreeFree to download and use indefinitely on computers you own or are authorized to use · participation is free of charge

The facts

Each one read from Prime95's own pages, with the date it was checked.

The company

Founded
1996checked 28 Sep 2026
Maker
Mersenne Research, Inc. owns and operates Mersenne.org and is described as a California nonprofit organized for mathematical and computer science research and related education.checked 7 Oct 2026

What it does

Hardware support
The page says recent NVIDIA or AMD discrete GPUs may be more powerful than a CPU for prime testing or factoring, with separate GPU programs communicating with PrimeNet through AutoPrimeNet.checked 7 Oct 2026
License and warranty
The EULA allows indefinite free use on computers owned by the user or where they have permission, and provides the software and information as is without warranty.checked 7 Oct 2026
Participation
GIMPS participation is free of charge and open to the public internationally.checked 7 Oct 2026
PrimeNet coordination
The program contacts PrimeNet to receive work, and users can view computer progress and remotely control work assignments from the account CPUs page.checked 7 Oct 2026
Privacy
GIMPS says it will not sell, distribute, or release participants’ email addresses or other supplied information except where required by law.checked 7 Oct 2026
Purpose
Prime95 is free Mersenne prime search software used to participate in GIMPS.checked 7 Oct 2026
Resource controls
Version 30.3 introduced a Resource Limits dialog to control Prime95 resource usage.checked 7 Oct 2026
Source code
The source archive is listed for Windows, Linux, FreeBSD, and Mac OS X, and the page describes the code as highly optimized Intel assembly and completely non-portable.checked 7 Oct 2026
Stress testing
Prime95 runs a heavy, consistent workload across CPU cores to test CPU and L1/L2/L3 cache stability.checked 7 Oct 2026
Support
The download page directs users to the Mersenne Forum for help and lists email contacts for networking/server issues and other software questions.checked 7 Oct 2026
Supported downloads
The current download page lists Windows, Linux, Mac OS X command-line, and FreeBSD builds.checked 7 Oct 2026
Test types
The download page lists PRP tests, Lucas-Lehmer tests, P-1 and ECM factoring, and trial factoring among its project work and software features.checked 7 Oct 2026

Where it runs

Windows service
A GUI-less Windows service build is available for administrators, and the page says it is for Windows Server experts only.checked 7 Oct 2026

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