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How to Stress-Test CPUs and PCs (Like We Do)

CPU Only: Prime95 With AVX Or SSE

Prime95 is to CPUs what FurMark is to GPUs: a true classic that continues receiving updates. Current versions support the AVX instruction set, which helps generate massive thermal loads. Not everyone finds it necessary to go all-out with temperatures, though. For those folks, the BIOS on motherboards offers AVX offset adjustments to reduce clock rates as AVX instructions make their way through the execution pipeline. Alternatively, you can download an older version of Prime95, before it was optimized for AVX support.

Before we show you how to switch between instruction set extensions, you'll want to download Prime95 here.

Selecting the Instruction Set Extension

By default, Prime95 automatically selects the newest instruction set extension, such as AVX, AVX2, or even AVX-512. In order to change this behavior, Prime95 needs to be started and completely shut down again once. This will create the local.txt file. In it, exclusions are assigned a value of 0, whereas the code path that’s to be tested is assigned a value of 1. If you aren’t clear as to which SSE version is supported by your CPU, both can be set to 1. Prime95 will choose the correct fallback.

    CpuSupportsRDTSC=0 or 1    CpuSupportsCMOV=0 or 1    CpuSupportsPrefetch=0 or 1    CpuSupportsSSE=0 or 1    CpuSupportsSSE2=0 or 1    CpuSupports3DNow=0 or 1    CpuSupportsAVX=0 or 1    CpuSupportsFMA3=0 or 1    CpuSupportsFMA4=0 or 1    CpuSupportsAVX2=0 or 1    CpuSupportsAVX512F=0 or 1

Prime95 With AVX & Small FFTs

We start at the top and let Prime95 automatically activate AVX by skipping manual entries. The Small FFTs setting maximizes temperatures, even though memory isn’t taxed as much. Our results show this well:

CPU Package(PECI)CoreAverageSensorSocketMemoryCPU (Watts)System (Watts)
Compared to Maximum100%100%100%77.8%100%100%
AssessmentExtremely high package temperature for stability testsSomewhat low memory temperatureVery high CPU and system power consumption
Use forPower consumption measurementsCooling test close to the limit

Prime95 With AVX & Blend

Using the more conservative Blend test results in less load on the cores and more load on the memory. This is a viable alternative for pure stability testing meant to detect possible computational errors due to a potentially unstable overclock, especially since it’s suitable for prolonged test runs (providing your cooling solution is up to the task).

CPU Package(PECI)Core AverageSensorSocketMemoryCPU (Watts)System (Watts)
Compared to Maximum62.1%61.1%72.4%94.4%75.6%63.5%
AssessmentNormal package temperatureHigher memory temperatureAverage CPU and system power consumption
Use forProlonged stability testMemory test (overclocking)

Prime95 With SSE & Small FFTs

Once AVX is manually disabled, Prime95 becomes a much better measure of stability. Most real-world applications don’t use AVX, after all. A longer test to detect possible overclocking-related instability makes more sense this way, even if we think you should still run a round of benchmarks using real-world workloads.

CPU Package(PECI)Core AverageSensorSocketMemoryCPU (Watts)System (Watts)
Compared to Maximum86.2%86.0%78.1%77.8%62.2%63.5%
AssessmentHigher package temperatureSomewhat low memory temperatureSomewhat higher CPU and system power consumption
Use forProlonged stability testSimple cooling test

Prime95 With SSE & Blend

As before, using Blend instead of Small FFTs increases the memory load while easing up on the execution cores somewhat. Knowing when to pick this combination of settings is difficult, since it's perhaps the least-taxing of all. We consider it well-suited to systems without the best cooling, such as laptops and mini PCs.

CPU Package(PECI)Core AverageSensorSocketMemoryCPU (Watts)System (Watts)
Compared to Maximum60.9%60.5%66.7%94.4%57%57.9%
AssessmentLow package temperatureHigher memory temperatureLowest CPU and system power consumption
Use forProlonged stability test for systems with weak cooling (laptops)Memory test (overclocking)


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