Prime95 on Mac: The mprime Guide for macOS

Quick facts: On macOS, Prime95 30.19 build 20 is a command-line program called mprime. There is no Mac GUI, no .app bundle, and no DMG installer. The official MacOSX package contains just a handful of files, centred on the mprime binary and its text documents. That binary is built for Intel x86_64 only, with no Apple Silicon slice, so on an M-series Mac it runs through Apple’s Rosetta 2 translation. That last point follows from the binary’s architecture; it is an architecture-based explanation, not a separate Apple Silicon edition, because no such edition exists in the official package.

Download the Mac package

Get the package from the download page or via the official direct link go/prime95-mac-official to mersenne.org. The MacOSX tar.gz package for 30.19 build 20 is 4,464,665 bytes, and the download page lists its verified SHA-256 and MD5 so you can check the file after downloading. If a site offers a Mac Prime95 .app, a DMG, or an Apple Silicon native build of this version, that offer does not match the official package described here. Stick to the archive whose checksum you can verify, extract it yourself, and run the binary from Terminal.

Extract to a writable folder

Create a folder in a place your account can write to, such as a Prime95 folder in your home directory, and extract the archive there. mprime stores prime.txt, work files, and result logs beside the binary, so the folder must remain writable and should not be a temporary download location that macOS may clear. After extraction you will see mprime plus the text files that ship with every platform, including readme.txt and stress.txt. There is nothing to drag into Applications and nothing to install. Keeping the folder intact is the whole installation, and deleting the folder is the whole uninstall for a machine you only used for testing.

Apple Silicon and Rosetta 2, stated plainly

On an Intel Mac, mprime runs natively. On an Apple Silicon Mac, the first launch of an Intel binary normally prompts macOS to offer Rosetta 2 installation if it is not already present; accept that system prompt if you want to proceed, because without translation the x86_64 binary cannot run on the ARM processor. Performance under translation is not the same as a native build would be, which matters if you use mprime for GIMPS throughput comparisons. For a stability check the translation layer does not change the meaning of the test: mprime still computes known problems and compares the results, and a mismatch still points first to hardware settings, memory, or heat. Do not interpret any speed difference between an Intel Mac and an Apple Silicon Mac running this binary as a pure processor comparison.

Run mprime from Terminal

Open Terminal, change into the extracted folder, and start the menu:

./mprime -m

The menu is where you choose between joining GIMPS through PrimeNet and using the program only for stress testing, configure workers, and launch the Torture Test. For a hardware check, take the stress-testing path. The Torture Test presets carry the same official meanings as on every platform: Smallest FFTs test the L1 and L2 caches; Small FFTs test L1, L2 and L3 caches with maximum power, heat and CPU stress; Large FFTs stress the memory controller and RAM; Blend, the default, tests all of the above. Since version 29.8 the FFT sizes are chosen automatically from cache size. The official duration guidance in stress.txt is 6 to 24 hours for a thorough run, unstable machines often fail within minutes, and 10 to 15 minute runs are for quick tuning steps only. On a Mac laptop, run on mains power, keep vents unobstructed, and watch temperatures with a Mac monitoring utility, because a thin laptop cooling system is often the limiting factor long before the processor is.

Stopping, logs, and what an error means

Stop the test from the mprime menu rather than force-quitting Terminal, so the program can finish writing its files. Then read the results output in the same folder. A completed entry means that worker’s computation matched the known result for that test. A rounding error or hardware failure message means it did not, and stress.txt guidance says to suspect hardware first: unstable settings, memory problems, or overheating, unless the identical error repeats at the identical place every time. Save the log lines and the time the worker stopped before changing anything. On a stock Mac with no tuning options, an error is still useful evidence for a support conversation, especially if it repeats across runs at the same settings.

Laptops, desktops, and sustained load on a Mac

The same mprime menu behaves differently in practice depending on the Mac’s cooling design. A desktop Mac with larger fans and a roomier case can usually sustain a long run with temperatures that level off, while a thin laptop may reach its thermal limit quickly and reduce clock speed to protect itself. That throttling does not invalidate the correctness check, because mprime still compares every result, but it does mean the run is testing the machine at the speed its cooling allows rather than at its short-burst speed. For a fair repeat test, use the same power connection, the same surface, and a similar room temperature, and note those conditions beside the log. If a laptop cannot complete a long run without severe throttling, treat that as useful information about sustained-load suitability, not as a reason to block vents or override fan behaviour to force a pass.

What mprime on Mac cannot do

It cannot give you the Windows graphical experience, because that interface exists only in the Windows build. It also does not test the Mac’s graphics processor, storage, or display pipeline; it stresses CPU and RAM, with cooling and power delivery stressed indirectly. There is no official iPhone or iPad version to continue a test on mobile, either. Treat mprime as one focused instrument: excellent at exposing CPU and memory calculation errors under sustained load, silent about everything else.

Next steps

Compare platforms on the platforms page, follow the general workflow in How to Use Prime95, and browse the tutorials hub for preset and results guides.