Guide: Stability testing with Prime 95

In this short guide I will explain how you can test the stability of your computer using the tool Prime 95. Overclocking causes instabilities at a certain point if you either reach the thermal or the electrical limit of your CPU. To see if your system is stable, Prime 95 is a very simple way to test.

First of all, you need the Prime 95 tool. Pick the version according to your operating systems:

Prime 95 v28.5 64-Bit
15.39 MB | 35486 downloads

Prime 95 v28.5 32-Bit
4.13 MB | 1388 downloads

You can also find different versions of Prime 95 in the Download Section.

The latest Intel CPUs feature the AVX instruction. Prime 95 27.7 and newer versions supports the AVX instruction which results in a higher load and core temperature. This will result in a lower overclockability, but a higher stability. However, almost no program or game can handle the AVX instruction. If you’re not using anything which features AVX, you can use Prime 95 26.6 without AVX so you might reach higher clocks.

Note: AVX only works with Windows 7 Service Pack 1 and newer.

It’s very important to keep an eye on the CPU core temperature. I recommend to use the tool Core Temp to check the temperature.

CoreTemp 1.0 RC6
717.26 KB | 11495 downloads
CoreTemp 1.0 RC7
301.49 KB | 6161 downloads


Once you got both tools ready, start Core Temp and check if you can see the temperature of all cores and if they make sense. On some AMD CPUs you will have odd values like a core temperature below the ambient temperature. This is not possible and if you experience this, check for a different tool to read out the core temperature. You can simply comment on this posting if you need help.

In the next step launch the Prime95.exe. You should now see something like this:



Click on “Just Stress Testing” to access the test settings.


Prime 95 comes with several different test options. Depending on which part of your system or CPU you want to test, you have to select the specific option.

I always recommend to use the “Custom” test with your own settings. The “Number of torture test threads” should be the same like like the threads of your CPU. For example if you use an i7-4770K with 4 Cores / 8 threads you should use 8 torture test threads. If you are unsure about the amount of threads of your system, simply open your taskmanager and count the amount of threads. Usually Prime95 detects the correct amount of threads and you don’t have to change it.

The correct torture test settings are important to test the right things of your system. These are the most important FFT sizes:

  • 1344K: High load on the core and the core voltage
  • 8K: Maximum heat production to test your cooling solution
  • 800K: Test RAM stability
  • 864K: Test the whole system

If you are overclocking your CPU, the first step would be to test the core clock. Set the Min FFT and Max FFT size to 1344 and check “Run FFTs in-place”. Also make sure that the time is set to 15 minutes.


Run this test for about 30 minutes to see if your CPU core is stable or not. Always check the temperature in Core Temp at the same time to make sure it does not exceed the maximum temperature of your processor.

Maximum recommended temperatures:

  • Intel Haswell (E): 90 °C
  • Intel Devils Canyon: 90 °C
  • Intel Ivy Bridge (E): 90 °C
  • Intel Sandy Bridge (E): 90 °C
  • AMD Vishera / Bulldozer: 75 °C
  • AMD Kaveri / Trinity / Richland: 75 °C


If it passed 1344K test for 30 minutes, you can either keep on tuning your CPU or go on with a full system test to see if it is 24/7 stable. Set the torture test to a Min FFT size of 8K and the Max FFTs to 4096K. Make sure “Run FFTs in-place” is still checked and the time is also still set to 15 minutes.


Prime95 will now run a full test in the following order:

448k, 8k, 512k, 12k, 576k, 18k, 672k, 21k, 768k, 25k, 864k, 32k, 960k, 36k, 1120k, 48k, 1200k, 60k, 1344k, 72k, 1536k, 84k, 1728k, 100k, 1920k, 120k, 2240k, 140k, 2400k, 160k, 2688k, 192k, 2880k, 224k, 3200k, 256k, 3456k, 288k, 3840k, 336k, 400k, 480k, 10k, 560k, 16k, 640k, 20k, 720k, 24k, 800k, 28k, 896k, 35k, 1024k, 40k, 1152k, 50k, 1280k, 64k, 1440k, 80k, 1600k, 96k, 1792k, 112k, 2048k, 128k, 2304k, 144k, 2560k, 168k, 2800k, 200k, 3072k, 240k, 3360k, 280k, 3584k, 320k, 4000k, 384k, 4096k

Usually this will take about 21 hours. So only run the full test if you really want to keep the settings for your 24/7 system.


If Prime95 simply stops running with an error, your system is most likely unstable. Raise voltages if you still have room in the temperature or lower the clocks.

You might also experience bluescreens during the torture test. The hex value in the bluescreen can be an indicator to find the issue. However these values might change from generation to generation.

  • 0x00000124: Core clock is unstable. You need a higher core voltage
  • 0x00000101: Input voltage (Intel Haswell) or Uncore (Intel Haswell)
  • 0x00000050: RAM is unstable. Lower clock or raise memory voltage

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  • DeathMade

    Hi, I am running Win8.1, but in this OS there are no informations in bluescreens anymore(it just says “:( something went wrong, we will restart your PC”) Is there any way to find bluescreen report?

  • Carlos Ramos

    I had a major problem with Core Temp RC6, had to use a quick fix RC7 as the previous version froze my pc entirely. If you google this issue, you’ll find people had this problem aswell. I think it’s related to Win 8/8.1

  • Federico

    15 minutes per FFT seems too high. I have used this guide and the test have already been running for 19 hours and it is in the 224k FFT. This is in i5 3570k @ 4.4GHz 1.26 VCore. This test will take more than 48 hours to complete.

    Thanks in advance

    • SoSleepy

      Really late to this thread but will comment anywhere for anyone that goes here. That doesn’t seem right. I’m running the same test but on my 6700k 4.5 ghz @ 1.325 V. 11 hours in to the test I’m already looping at 400k. Differences in cpu should not change the order and time of each fft loop.

      Anyway, thank you for all the great information der8auer. It was only a few months ago that I started overclocking as a hobby and found/read through so many of your guides and articles. Can’t wait what you have for us 2017+

      • Mark

        I am stress testing an underclocked i5-7600K at 2.1 GHz @0.700 V, and I got to 4096K after around 10 hours. But when it starts over the smaller numbers of each pair are different (after 576k comes 16k instead of 18k, for example). It’s only doing two tests per level, which it hasn’t been doing when I stress test an overclock. Any ideas as to what is going on?

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  • kongasdf

    I have some question, are these right?
    0x00000124: Core clock is unstable. You need a higher core voltage
    0x00000101: Input voltage (Intel Haswell) or Uncore (Intel Haswell)
    I think swapping of these two content

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  • RollingMountain

    I use an Intel i7 4770k CPU which I want to overclock. I don’t really want to bump it to the limits, only some more performance because I have an air cooler (Alpenföhn Brocken 2). I heard stories about Prime95 versions that can damage your CPU, so does it matter which version I use for an i7 4770k to test it for a 24/7 OC?

    PS: Keep up the great work, Grüße aus Berlin.

  • Connor

    For those who want to use latest p95 version and disable AVX2/FMA3 because of temperatures issues it can have, just open p95 folder, edit local.txt file and add the following line in it :


  • Connor

    1344K = Vcore
    448K = Vrin/Input
    512-576 = Cache/Uncore
    672-720K = VTT
    768K = Agent/IMC
    800K = Vdimm/Timings
    864K = All

    Source :

    May be someone can translate a bit 🙂

  • barry mullans

    hi I’m running a hp 23 in 1 touchscreen with 8 gig of ram 64 bit windows 10 I’m a newbie and don’t understand I can ajust my cpu overdrive from 3700 MHz to 4500mhz whats a recommended safe level

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  • Tony

    I ran 1344K on Prime 95 28.7 without problems , then went I tried to do a 8K my temps reached 99ºC and hit thermal throttling, no crashes so far, is it okay to use Prime 95 26.6 to do the rest of the tests?

    My plan is to do full system test and then run x264 for 24 hours too and then just normal PC usage.

  • MattbaneLM

    conner, that enables avx in v28.7

  • bob

    on sandybridge
    101= vcore
    124= vcore or vccio

  • Jacob

    Hi, I’m have a i5-6500 on a MSI Z170A SLI PLUS motherboard, I did the things, and everything seems fine, but all my monitoring software is reading 100C. MSI Afterburner is showing 100, Speedfan is showing 100, HWMonitor isn’t showing any temperature at all, but HWiNFO is showing 33C. Did a sensor break? What happened with the bios update that monitoring software is weirding out?

    • Tim

      Only skylake processors with a k in their name officially support overclocking (e.g i5 6600k).
      However some bios versions allow you to overclock ‘non-k’ cpu’s like the i5 6500. One of the downsides of this unoffical overclocking is that you cannot read core temperature, and thats why it often shows up at 100.

      Google around for skylake non-k overclocking to see exactly what other downsides there are.

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  • Skylinestar

    Just wanna give an update based on my observation on Prime95 v29.3. I’m running the 24/7 final stability test as highlighted above (8-4096,fft,15 minutes) but the sequence is different. 400,8,480,12,560,16,640,20,720,24,800,28,896,32,1024,40,1152,50,1280,64,1440,80,1600,96,1728,112,1920,2048,144,2400,168,2688,200,3072,240,3360,288,3584,336,448,10,512,15,576,18,672,21,768,25,864,30,960,36,1120,48,1200,60,1344,72,1536,84,1680,100,1792,120,2016,140,2304,160,2560,192,2880,224,3200,256,3456,320,3840,384,4000. Completed the run approx 21hrs.

  • Jalte

    if I run the final stability test, do I need to then also after test my ram (800k) and whole system (864k)?

  • Alex M

    In newer/older versions of Prime95, will the order of the custom test still be the same as described above?

    For 8700K, can I still run Prime95 26.6 or should I download a newer version?

  • Nares

    I think there is a problem with stability testing with non-AVX/FMA3 Prime95 and Win10. It gives false stable results, at least in my PC.
    First of all, I get much better OC result in Win10 vs Win7. In Win7 I can’t stabilize my coffee lake at 5.2 at all. 5.1 only. While Win10 allows me go 5.2. Seems like there something in Win10 that stabilizes higher OC’s, but do not always work.
    Secondly in Win10 I can pass 1 hour Prime95 26.6 at 1.355V. But system fails SSD benchmark until 1.37V and fails within minutes in some (older) games until 1.38V.
    In Win7 it works well since the OC is just lower with higher voltage on this OS.

  • Andrew

    Hi, could you kindly share the algorithm you used to determine the FFT values.

    Would like to understand how you came to your results.


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  • Amir

    Hi, in your second torture test (8k – 4096k) why are you running it with Run FFTs in-place ticked? Isn’t this supposed to use a small part of memory over and over again? Isn’t it better to have Run FFTs in-place unticked so that various parts of ram gets stressed to check chipset and memory stability?

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