Prime95 29.4b8

February 21st, 2018 - What's New
  • 6.1 MB
    Win 10, 8, 7 (64-bit)
  • 5.3 MB
    Win 10, 8, 7 (32-bit)

Prime95 29.3

Latest Stable
September 11th, 2017 - What's New
  • 6.0 MB
    Win 10, 8, 7 (64-bit)
  • 5.1 MB
    Win 10, 8, 7 (32-bit)
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Publisher: GIMPS
Downloaded: 41,579 times (74.2 GB)
Popular system stability test program.

Version History

29.4b8 (February 21st, 2018)

1) GIMPS has a new sub-project -- finding (probable) prime Mersenne cofactors.

This sub-project has two parts: 1) Running PRP tests, and 2) Finding additional factors. To support this new sub-project there are three new work preferences: PRP on Mersenne cofactors, PRP double-checking on Mersenne cofactors, ECM on Mersenne cofactors.

2) Like LL tests, PRP tests now support shift counts to aid in running double-checks. Shift counts are only supported for Mersenne numbers and Mersenne cofactors.

3) PRP tests now support a type of low overhead error checking that almost guarantees correct results even on flaky hardware. We call this Gerbicz error-checking after it was proposed by Robert Gerbicz at This error-check only works for base-2 numbers.

4) Because PRP tests are highly reliable, we now offer the option to do PRP tests instead of Lucas-Lehmer primality tests. There are 3 new work preferences similar to LL work preferences: first-time PRP tests, world record PRP tests, PRP tests on 100 million digit numbers, and PRP double-checking. If you are looking for a 100 million digit prime, PRP testing is recommended rather than LL testing.

5) For non-base-2 PRP tests, there is a new option to run each iteration twice and rollback if a mismatch occurs. Useful only on flaky hardware due to the obvious high overhead.

6) Minor performance tweaks were made to stage 1 of P-1. Save files are incompatible in stage 1. Wait for your P-1 test to reach stage 2 before upgrading.

29.3 (September 11th, 2017)

  • A new error check for LL testing has been implemented. This error check, called a Jacobi error check, has a 50% chance of detecting hardware error(s) since the last time a Jacobi error check was performed. This error check takes roughly 30 seconds and is scheduled to run twice a day. The program now saves two additional intermediate files that have passed the Jacobi error check. This test requires use of the GMP (GNU multi-precision) library.
  • The GCD step in P-1 and ECM factoring is faster.

29.2 (June 10th, 2017)

  • Throughput benchmarks of all FFT implementations are written to gwnum.txt. These benchmarks will then be used to pick the best FFT implementation to use. This can lead to minor performance improvements.
  • Benchmarks are run daily for any FFT sizes that will be needed within the next 7 days. Once enough benchmark data is accumulated, automatic benchmarks no longer take place.
  • Default FFT implementations for Ryzen added. 4) A few new FFT sizes (up to 50M) are enabled for FMA3-capable CPUs.

29.1 (March 27th, 2017)

  • Faster trial factoring for machines that support FMA (Haswell and later). Multi-threaded trial factoring now supports more than one thread sieving for small primes. Several tuning parameters added - see undoc.txt.
  • The portable library, hwloc, for analyzing a machine's topology is now used. This replaces the buggy code prime95 used to detect hyperthreading. It also eliminates the need for AffinityScramble2. Running a benchmark will output this topology information to results.txt.
  • AVX-512 trial factoring support added.
  • Dialog box for benchmarking added.
  • In the Test/Worker Windows dialog box you no longer choose how many threads each worker uses. Instead, you choose how many CPU cores each worker uses. There affinity options have been removed. There are two new options that will decide if each worker also uses hyperthreading.