Overclocked a CPU or built a new PC and want to know it’s stable under full load? Prime95 uses mathematical workloads to check CPU stability, and it can also take part in the Great Internet Mersenne Prime Search (GIMPS).
Choosing a Torture Test
Select Just Stress Testing at startup to open the torture-test setup, then choose a workload. Small FFTs focuses on CPU calculations with a small working set; Blend varies the FFT sizes and uses more memory. Large FFTs and the Custom option provide other test configurations.
These workloads keep calculations running continuously, which can expose errors that do not appear during lighter use. Prime95 reports each worker’s progress in the main window; calculation errors or a worker stopping are signs that the test did not complete cleanly.
- Use Small FFTs to emphasize the processor and its cache.
- Choose Blend to include memory in the test workload.
- Set up a Custom test when the preset workloads do not match the test you want to run.
Reading Worker Activity
Prime95 organizes its work into worker threads, with status information for each one. During a stability test, the worker entries show whether calculations are continuing or have reported an error.
A completed run without reported errors is evidence that the system handled that particular workload. It does not establish that every application or workload will behave identically.
GIMPS Prime Searches
Prime95 also performs calculations for GIMPS, a distributed effort to find Mersenne primes. Participants contribute computer time to assigned mathematical tests. The program’s prime-search work and its torture-test mode use intensive calculations, but serve different tasks: one contributes results to the search, while the other puts sustained load on a system to check stability.
Pros
- Torture Test offers Small FFTs, Large FFTs, Blend, and custom settings
- Worker status makes calculation errors visible during a test
- GIMPS options support searching for Mersenne primes
Cons
- Extended torture tests sustain a heavy processor load and can increase heat
System requirements: Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11 · 32-bit and 64-bit
What does the Blend test check?
Blend varies FFT sizes and uses more memory while running continuous calculations, exercising both the CPU and memory.
What does a Prime95 calculation error mean?
It means a worker reported an incorrect calculation during the test. That can indicate system instability under the workload.
Can Prime95 search for Mersenne primes?
Yes. Prime95 can contribute mathematical work to GIMPS, the Great Internet Mersenne Prime Search.