Prime95 on Windows 11: Download and Run the Stress Test

Prime95 is a freeware program by George Woltman for GIMPS, the Great Internet Mersenne Prime Search, and the name covers the Windows graphical version of the program. Other systems use a command-line version called mprime, but Windows 11 gets the full graphical program described on this page. Its Torture Test stresses CPU and RAM by comparing continuous calculations against known correct results, which is why builders use it to validate a new PC, an overclock or a repair. This page covers the complete Windows 11 flow in order: get the exact file, verify it, extract it correctly, launch it the right way, and run a first test you can interpret. The platform overview lives on the platforms hub, and the Windows sections of the main download page are written for this same intent.

Step 1: Download the exact Windows 11 package

Use the official direct link go/prime95-win64-official, which points to the verified package on mersenne.org, or start from the download page, whose Windows 11 section lists the same file with its size and checksum. The file you should receive is p95v3019b20.win64.zip. If the filename differs, if the size is not 8,805,545 bytes, or if a site offers you an installer, a setup wizard or a Windows 11 edition of Prime95, stop and get the file from the link above instead, because the official program is distributed as this single zip package and has no installer. A 32-bit package also exists for old 32-bit Windows installations, but a normal Windows 11 system is 64-bit and should use the win64 package named here.

Step 2: Verify the file before you run it

Verifying the download takes a minute and proves the file arrived complete and unchanged. Open the folder containing the zip, then compare its SHA-256 with the value in the quick answer above: d9475f2ff3f4a6a701abc49a86a66126cb48abd10bda6fa87039d98fa8756bca. Windows can produce the hash from a command prompt or PowerShell window with its built-in checksum utility, and any reputable hash tool will do the same job. If the value matches exactly, the file is the verified official package whose hash was checked against the file on mersenne.org. If it does not match, delete the download and fetch it again from the official link rather than running a file you cannot account for. This one habit removes an entire category of doubt later, when a test result needs to be trusted.

Step 3: Extract to a writable folder

Right-click the zip and extract all of its contents into a new, writable folder, for example a Prime95 folder in Documents or on a data drive. Do not run prime95.exe from inside the zip preview, and do not accept an extraction wizard’s temporary folder as the program’s home. Prime95 keeps its settings in prime.txt and its logs, including results.txt, in the same folder as the executable, so the folder must stay writable and stay put. A folder inside a protected system directory is a poor choice because a normal user account may not be able to write there, which breaks the portable design. After extraction you should see prime95.exe together with its supporting library files and the included text documents, among them readme.txt and stress.txt. Keep the whole set together; moving the executable out on its own leaves required files behind.

Step 4: Launch and choose Just Stress Testing

Double-click prime95.exe. You do not need to right-click and run as administrator, and a normal stress test does not need an installer, a service or a reboot. On first launch the program offers a choice between joining GIMPS, where your computer searches for Mersenne primes and reports to the PrimeNet server, and just stress testing. For validating hardware, choose Just Stress Testing. Then open Options, then Torture Test, and pick a preset. Smallest FFTs test the L1 and L2 caches with high power and heat. Small FFTs test the L1, L2 and L3 caches with maximum power, heat and CPU stress, making that preset the right one for finding a temperature ceiling. Large FFTs stress the memory controller and RAM. Blend, the default, tests all of the above, and since version 29.8 the sizes are chosen automatically from your CPU cache. The full beginner workflow, including how to stop a test and read its outcome, is in How to Use Prime95.

Step 5: Monitor, run for a meaningful length, and record the result

Keep a monitoring tool open during the run so you can watch CPU temperature, clocks and power rather than guessing from fan noise. There is no single official safe temperature in Prime95’s documentation that fits every processor, so check the limit for your exact model on the manufacturer’s specification page. For duration, follow the one official source: the stress.txt guide included with the program recommends 6 to 24 hours for a thorough check, notes that unstable machines often fail within minutes, and reserves short 10 to 15 minute runs for exploring each step of an overclock before a long final test. When you stop, use Test, then Stop, so the logs are written cleanly, and keep results.txt with a note of the preset, the run length and your system settings. If a worker stopped on its own with an error, that is a real result: the calculation did not match the known correct answer under those conditions, and the next step is diagnosis at more conservative settings, not an immediate identical rerun.

Frequently asked questions

What is the exact Prime95 file to download for Windows 11?

The Windows 64-bit package for Prime95 30.19 build 20 is p95v3019b20.win64.zip, 8,805,545 bytes, with SHA-256 d9475f2ff3f4a6a701abc49a86a66126cb48abd10bda6fa87039d98fa8756bca.

Do I need to install Prime95 or run it as administrator on Windows 11?

No. Prime95 is portable on Windows 11: extract the zip to a writable folder and double-click prime95.exe. No installer and no administrator account are needed for a normal stress test.

Does Prime95 work differently on Windows 11 than on Windows 10?

No, there is no essential difference. The same Windows 64-bit package is used on Windows 11 and Windows 10, and the Torture Test presets, settings and result checking work the same way on both systems.

How long should I run Prime95 on Windows 11?

The stress.txt guide included with Prime95 recommends running the Torture Test for 6 to 24 hours for a thorough stability check. Unstable systems often fail within minutes, and short runs of 10 to 15 minutes are only for exploring overclock steps.

Next steps

For the complete workflow beyond Windows 11 setup, read How to Use Prime95. For the same flow on the older system, see the companion page for Windows 10, and return to the download page whenever you need a fresh, verified copy of the package. Platform-wide guidance, including AMD, Intel, laptop and older hardware notes, is indexed on the platforms hub.