prime95 test question


May 18, 2010
just started overclocking my 4670k and was playing with the options on prime 95. seams like most sites tell you to use small fft or blent.

my question is why not large? i only ask this cause i picked large and it made my cpu run WAY WAY hotter than either of the other two. or is that more of a thermal testing option more than any thing else.

blend is running right now at 75c or less but large was at about 90c solid and consistant.


Intel Master
Do NOT run any versions of Prime95 later than 26.6. Here's why:

Core i 2nd, 3rd and 4th Generation CPU's have AVX (Advanced Vector Extension) instruction sets. Recent versions of Prime95, such as 28.5, run AVX code on the Floating Point Unit (FPU) math coprocessor, which produces extremely high temperatures. The FPU test in the stability testing utility AIDA64 shows the same results.

Prime95 v26.6 produces temperatures on 3rd and 4th Generation processors more consistent with 2nd Generation, which also have AVX instructions, but do not suffer from thermal extremes due to having a soldered Integrated Heat Spreader and a 35% larger Die.

Please download Prime95 version 26.6 -

Run only Small FFT’s for 10 minutes.

Use only Real Temp to measure your Core temperatures, as it was designed specifically for Intel processors: Real Temp -

Your Core temperatures will test 10 to 20C lower with v26.6 than with v28.5.

Please read this Tom’s Sticky: Intel Temperature Guide -


CT :sol:


Sep 28, 2014
Hey man. Prime 95 is really inaccurate and unnecessary to determining if your system is stable. Under no circumstances will your cpu ever come close to the temps and stress prime 95 puts the cpu at.

A better tool to use is intel xtreme utility and use the feature there called stress test. Don't bother with prime 95.

And to answer the question large is a more intense test than the others. (Large stress) The blend option is giving you lower temps because it is a mixture of low range, mid range, and long etc.


Jan 23, 2015
using OCCT and Aida64 is great and all but nothing beats real world scenarios, Run x264 for a couple of hours. your PC might pass a few hours of Prime95,OCCT,aida64 but might fail a couple of mins into Rendering.


Intel Master
Since everyone tests their rigs using X stress software at Y Ambient temperatures with Z measuring utilities resulting in CPU or Package or Core temperatures, it's impossible to compare apples to apples. This is why processor temperatures are so confusing.

There are only three relevant values; Ambient, steady-state 100% workload, and dead idle. Applications and games are partial workloads with fluctuating temperatures, which are unsuitable for thermal testing or accurate temperature comparisons.

Prime95 Small FFT's is the standard for CPU thermal testing, because it's a steady-state 100% workload. This is the test that Real Temp uses to test sensors. The link above is to version 26.6, which is well suited to all Core i and Core 2 variants.

Prime95's default test, Blend, is a cyclic workload for testing memory stability, and Large FFT's combines CPU and memory tests. As such, Blend and Large FFT's both have cyclic workloads which are unsuitable for CPU thermal testing.

Other stability tests such as Linpack and Intel Burn Test have cycles that load all registers with all one's, which is equivalent to a 110% workload, and are also unsuitable for CPU thermal testing. The software utility OCCT runs elements of Linpack and Prime95.

Shown above from left to right: Small FFT's, Blend, Linpack and Intel Burn Test.

Note the steady-state thermal signatures of Small FFT's, which allows accurate measurements of Core temperatures.

Shown above from left to right: Small FFT's, Intel Extreme Tuning Utility CPU Test, and AIDA64 CPU Test.

The "Charts" in SpeedFan span 13 minutes, and show how each test creates different thermal signatures. Intel Extreme Tuning Utility is also a cyclic workload. Although AIDA64's CPU test is steady-state, the workload is well below TDP, and it's not available as freeware.

Keep in mind we're using Prime95 Small FFT's for thermal testing not stability testing.

CT :sol:


Intel Master
The key to thermal testing is using a workload which is steady-state. Intel's Thermal Specification (Tcase) is a calculation and a laboratory bench test, which must agree.

It's not possible to obtain accurate thermal measurements from fluctuating workloads that have fluctuating core temperatures which look like a bad day on the Stock Market (illustrated above in the Charts). As such, temperature averaging as a means to determine accurate core temperatures is inappropriate.

If you can't be convinced that p95 v26.6 is problem free, then the next best alternative which is also steady-state is HeavyLoad:

HeavyLoad provides core temperatures within 3% and power dissipation (watts) within 4% of Prime95 v26.6 Small FFT's.

CT :sol: