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Prime95
What it is
Prime95 is free software for searching for Mersenne primes and contributing computing work to GIMPS, an international public project. It can also place a heavy, consistent workload across CPU cores to check processor and L1, L2, and L3 cache stability. Prime95 contacts PrimeNet for assignments, while an account’s CPUs page lets participants view progress and manage work remotely. Listed project tasks include PRP tests, Lucas-Lehmer tests, P-1 and ECM factoring, and trial factoring. Downloads are available for Windows, Linux, Mac OS X command-line, and FreeBSD. Administrators can use a GUI-less Windows service build, which the download page reserves for Windows Server experts. Source archives cover Windows, Linux, FreeBSD, and Mac OS X; the code is described as optimized Intel assembly and non-portable. Version 30.3 added a Resource Limits dialog. Recent NVIDIA or AMD discrete GPUs may be more powerful than CPUs for prime testing or factoring, with separate GPU programs connecting through AutoPrimeNet. GIMPS participation is free of charge and open internationally.
For and against
For
- Free indefinite use
- CPU and cache stability workload
- PrimeNet assignment coordination
- Windows, Linux, Mac OS X, and FreeBSD builds
- Resource Limits dialog
Against
- Windows service build targets Server experts
- Source code is non-portable
- Use is provided without warranty
The verdict
Prime95 combines public prime-search participation with a demanding hardware workload and several project test types. Its multi-platform downloads and free participation support varied setups.
Who it suits
It suits people who want to contribute computer time to GIMPS or run sustained CPU workloads for processor and cache stability checks.
Plans and prices
Prime95
Free to download and use indefinitely on computers you own or are authorized to use · participation is free of charge
Read 7 Oct 2026 · mersenne.org
On the record
- 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.mersenne.org · read 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.mersenne.org · read 7 Oct 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.mersenne.org · read 7 Oct 2026
- Participation
- GIMPS participation is free of charge and open to the public internationally.mersenne.org · read 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.mersenne.org · read 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.mersenne.org · read 7 Oct 2026
- Purpose
- Prime95 is free Mersenne prime search software used to participate in GIMPS.mersenne.org · read 7 Oct 2026
- Resource controls
- Version 30.3 introduced a Resource Limits dialog to control Prime95 resource usage.mersenne.org · read 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.mersenne.org · read 7 Oct 2026
- Stress testing
- Prime95 runs a heavy, consistent workload across CPU cores to test CPU and L1/L2/L3 cache stability.mersenne.org · read 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.mersenne.org · read 7 Oct 2026
- Supported downloads
- The current download page lists Windows, Linux, Mac OS X command-line, and FreeBSD builds.mersenne.org · read 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.mersenne.org · read 7 Oct 2026
- Windows service
- A GUI-less Windows service build is available for administrators, and the page says it is for Windows Server experts only.mersenne.org · read 7 Oct 2026
