Prime95 has been around for decades, and the version you run affects which instruction sets it uses, which operating systems it supports and how hard it hits your CPU. This page summarises the version history from the official download page, explains what changed between the versions that matter for stress testing, and covers the Linux, macOS and FreeBSD builds in detail.
- The latest binary on the official page is 30.19 build 20, released 2024-06-02.
- A 30.19 build 21 (2024-09-14) is listed as source code only.
- Versions after 26.6 added AVX, and 29.8 added AVX-512 support, which is why newer versions run hotter.
- Linux, macOS and FreeBSD get command-line builds (mprime).
What is the latest Prime95 version?
The official download page lists 30.19 build 20, released on 2024-06-02, as the latest version. A newer 30.19 build 21, dated 2024-09-14, appears there as source code only, not as a ready-to-run binary, so it’s aimed at people who compile the program themselves. Always check the mersenne.org download page for updates, and see our Prime95 download page for direct links and verification steps.
Prime95 version history
The official page keeps older releases available. Here are the versions it lists, with the dates it shows.
| Version | Date listed | Notes |
|---|---|---|
| 26.6 | 2011-04-08 | Later versions added AVX, according to community reports |
| 27.9 | 2012-12-12 | Older release still listed |
| 28.7 | 2015-08-10 | Older release still listed |
| 29.2, 29.3, 29.4 | Various | Listed in the 29.x series |
| 29.8 (build 7 for Mac OS X GUI, build 6 for Windows XP) | 2020-03-19 and 2019-08-18 | AVX-512 FFT support arrived in 29.8, per release notes |
| 30.3, 30.7, 30.8 | Various | 30.7 build 9 for FreeBSD 11+ is dated 2021-11-15 |
| 30.19 build 20 | 2024-06-02 | Current stable binary |
| 30.19 build 21 (source) | 2024-09-14 | Source code only |
Source: the version list on mersenne.org/download. Some entries are listed per platform with their own dates, so check the page for exact details.
Why the version matters for stress testing
Prime95 is a program whose speed depends on the instruction sets it can use, and that’s also what decides how much heat it makes. Forum users have reported that Prime95 versions after 26.6 run hotter because they use AVX, and that was a noticeable jump for people who upgraded without realising. AVX-512 support, which arrived in 29.8, adds another step on CPUs that support it. The practical effect is that the same CPU and cooler can produce very different temperatures with different Prime95 versions, though those reports are anecdotal.
That has two consequences. When you compare stress-test results with someone else’s, check which version they ran. And if you’re following an old guide that says “my CPU never goes above 70°C in Prime95”, it may have been written for a version that didn’t use AVX. See AVX settings for how to control this.
Which version should you use?
Use the latest stable binary, currently 30.19 build 20, unless you have a specific reason not to. It’s the version the maintainers support, and it chooses the fastest instruction set your CPU supports. If you want a cooler or more realistic load, don’t downgrade to an old version. Disable AVX in local.txt instead, which keeps the modern code and lets you control the load. Older versions may also behave differently on newer CPUs, and the community advice to avoid certain older builds on new processors is a reason to stay current.
Prime95 on Linux
Linux gets a command-line build called mprime. The official page lists 64-bit and 32-bit archives.
- Linux 64-bit: p95v3019b20.linux64.tar.gz (5.6 MB)
- Linux 32-bit: p95v3019b20.linux32.tar.gz (4.5 MB)
- Download and extract.
tar -xzf p95v3019b20.linux64.tar.gz - Run mprime from a terminal in that folder:
./mprime - Answer the prompts. When asked about joining GIMPS, choose to stress test only, the same way you’d choose “Just Stress Testing” on Windows. According to the program’s readme, a
-tswitch starts the torture test directly, which suits scripts. Confirm the switches in the readme for your version.
Some users have reported crashes on Linux on specific CPUs with AVX2 enabled. One Intel community thread discusses a segmentation fault on a Core i9-14900K. That report is anecdotal and doesn’t establish a general fix, but disabling AVX2 as described in the AVX settings guide is a reasonable troubleshooting step.
Prime95 on macOS
The official page lists a command-line macOS build, p95v3019b20.MacOSX.tar.gz (4.3 MB), for Intel CPUs. Earlier in the history, a Mac OS X GUI build existed (29.8 build 7). If you’re on Apple silicon, check the official page for current support before relying on the Intel build, because compatibility and performance on Apple silicon aren’t something this page can promise. The usage is the same as Linux: extract the archive and run the binary from a terminal.
FreeBSD and other builds
- FreeBSD 12, 64-bit: p95v3019b20.FreeBSD12-64.tar.gz (5.9 MB)
- Windows service builds: 64-bit (6.7 MB) and 32-bit (5.7 MB) zips that run Prime95 as a background service for people donating computing time.
- Source code: the 30.19 build 21 source (37.7 MB) for people who build it themselves.
Upgrading safely
Download the new zip, extract it to a fresh folder, and copy over only the settings you actually need. Extracting on top of an old install can leave behind options from the previous version, which can change how the new one behaves. If you’ve edited local.txt, back it up first and re-apply your changes deliberately. When upgrading an existing GIMPS installation (not just a stress-test folder), keep your results and work files safe before replacing anything, and read the release notes for any change to file formats.
After upgrading, run a short test and compare temperatures with your last run. A newer build can behave differently on the same hardware. If it runs hotter or fails, see Prime95 errors explained, and use safe Prime95 temperatures to judge the heat.
What the release notes say changed, by version
The official Prime95 release notes are a long, plain-text changelog. These are the entries most relevant to stress testing and to running Prime95 day to day.
| Version | Change |
|---|---|
| 21.2 | Error messages such as ILLEGAL SUMOUT and SUMINP != SUMOUT are no longer sent to the server. Error counts are reported in the final result instead. |
| 22.6 | The Start At Bootup option now runs Prime95 as a Windows NT/2000/XP service. |
| 22.8 | The torture test uses up to the memory amount set in the Options/CPU dialog. |
| 23.5 | The program returns the error count with a prime result, and a nonzero count makes a reported prime more suspect. |
| 23.6 | There are now three flavours of torture testing (small FFTs, in-place large FFTs and a memory-heavy blend). The torture test stops after 100 ILLEGAL SUMOUT errors. |
| 25.5 | Config files renamed: prime.ini became prime.txt, local.ini became local.txt, worktodo.ini became worktodo.txt. Comment lines are now allowed. |
| 25.7 | DayMemory and NightMemory in local.txt replaced with a single Memory setting. |
| 26.2 | After a possible hardware error, later progress updates include a running error count. |
| 27.1 and 27.3 | AVX optimizations added for 32-bit and 64-bit builds. |
| 28.3 | FMA3 support added (tied to Haswell). |
| 28.5 | Mac: a preference to bypass some of Mac OS X Mavericks’ power-saving features. |
| 29.8 | AVX-512 FFT support. Torture test dialog options are now based on cache sizes, and torture tests that use all RAM are more stressful. |
| 30.1 to 30.3 | PRP proofs added, which require lots of temporary disk space. Proofs are auto-uploaded from 30.2. |
| 30.x | A warning is raised if temporary disk space is less than 1.5 GB. A resource limits dialog is added. |
What these changes mean if you only stress test
- Three torture-test flavours since 23.6: the Small, Large and Blend structure you see today has been stable for a long time, which is why old guides still map neatly onto the current dialog.
- Cache-based options since 29.8: the options in the torture test dialog are now based on your CPU’s cache sizes, so the exact FFT ranges differ from one CPU to another.
- All-RAM tests got harder in 29.8: the notes say tests that use all RAM are now more stressful, so an old Blend pass may not match a new one.
- Config files are plain text: prime.txt and local.txt have been plain text since 25.5, and you can add comment lines to document your changes.
- Disk space only matters for GIMPS: the PRP proof disk warning applies to project work, not stress testing.
The notes list no Linux entries in this file, and Mac appears only in one entry, so use the readme that ships with your download for platform specifics.
Frequently asked questions
Is there a newer version than 30.19 build 20?
The official page lists 30.19 build 21 as source code only (2024-09-14). Check mersenne.org for new binaries.
Does Prime95 run on Linux?
Yes. The command-line build (mprime) is available as a tar.gz for 64-bit and 32-bit Linux.
Does Prime95 work on Apple silicon Macs?
The official page lists a command-line macOS build for Intel CPUs. Check the page for current Apple silicon support.
Should I use an older Prime95 version?
Older versions without AVX run cooler, but the latest build is the better default. Use the AVX settings to control heat instead of downgrading.
What is the difference between Prime95 and mprime?
They’re the same program for different systems. Prime95 is the Windows build, and mprime is the command-line build for Linux, macOS and FreeBSD.
Where can I read the release notes?
The official download page links to a whatsnew file for each version. Read it before upgrading, especially if you use Prime95 for GIMPS work as well as stress testing.