i5 8600K 5.0GHZ Power Limiting in prime 95

tannerchampine,

On behalf of Tom's Moderator Team, welcome aboard!

Q: What is your ambient temperature? Standard or "normal" is 22°C or 72°F.

If you're running any version of Prime95 later than 26.6, then you might expect this type of problem. Later versions can push your processor to nearly 130% TDP due to imposing AVX Instruction Sets, whereas 26.6 is as close as you can get to 100% TDP, which doesn't overload or underload you processor.

Intel tests their processors at a steady 100% TDP to validate Thermal Specifications. Prime95 version 26.6 Small FFT's is ideal for CPU thermal testing, because it's a steady 100% workload with steady Core temperatures that typically runs Core i variants with Hyperthreading and Core 2 processors within +/- a few % of TDP. No other utility so closely replicates Intel's test conditions. This is the utility Real Temp uses for testing Core temperature sensors.

Utilities that don’t overload or underload your processor will give you a valid thermal baseline. Here’s a comparison of utilities grouped as thermal and stability tests according to % of TDP, averaged across five Generations of processors at stock settings:

TDP% ... Thermal Test - Steady Workload

129% ... Prime95 v27.7 through v29.4 - Small FFT’s (AVX)
105% … PowerMAX v1.00.1 - CPU - SSE
101% <-- Prime95 v26.6 - Small FFT’s
89% ... HeavyLoad v3.4.0.234 - Stress CPU
87% ... FurMark v1.19.1.0 - CPU Burner
78% ... CPU-Z v1.83.0 - Bench - Stress CPU
66% ... AIDA64 v5.95.4500 - System Stability Test - Stress CPU

TDP% ... Stability Test - Fluctuating Workload (Peak)

123% ... OCCT v4.5.1 - CPU: OCCT (AVX)
118% ... LinX v0.6.5 - Default
116% ... IntelBurn Test v2.54 - High
113% ... OCCT v4.5.1 - CPU: Linpack (AVX)
110% ... AIDA64 v5.95.4500 - System Stability Test - Stress FPU
99% <-- Asus RealBench v2.56 - Stress Test (AVX)
97% ... Intel Processor Diagnostic Tool v4.1.0.24 - Default
94% ... Sandra 2017.09.24.41 - Burn in - Processor Tests
92% ... CineBench v15.0 - CPU - Render Test
79% ... Intel Extreme Tuning Utility v6.4.1.15 - CPU Stress Test

All tests will show 100% CPU Utilization in Windows Task Manager, which seldom coincides with actual workload or % of TDP. Higher TDP tests produce higher Core temperatures. Overclocking increases measured Power (Watts). TDP varies with Microarchitecture, Core count, Core speed, Core voltage, VID, Turbo Boost, Hyperthreading, Instruction Sets, Memory, IGPU, CPU cooler, BIOS settings, versions and Microcode.

2nd through 8th Generation i3, i5 and i7 CPU's have AVX (Advanced Vector Extension) Instruction Sets. Prime95 versions later than 26.6 run AVX code on the CPU's Floating Point Unit (FPU) which causes unrealistic temperatures up to 20°C higher due to excessively high TDP workloads, as shown above. Other high TDP utilities have similar results.

AVX can be disabled in Prime95 versions later than 26.6 by inserting "CpuSupportsAVX=0" into the "local.txt" file in Prime95's folder. However, since Core temperatures will be the same as 26.6, it's easier to just use 26.6. AVX doesn't affect Core i 1st Generation, Core 2, Pentium or Celeron processors since they don't have AVX Instruction Sets.

• Prime95 v26.6 - http://www.mersenneforum.org/showthread.php?t=15504

If you run AVX apps such as for rendering or transcoding, you may need to reduce Vcore and Core speed or upgrade your cooler and case fans. Many 6th, 7th and 8th Generation motherboards address the AVX problem by providing offset adjustments in BIOS. An offset of -2 or -3 (200 or 300 MHz) is usually sufficient.

Asus RealBench runs a realistic AVX workload typically within +/- a few % of TDP, and is an excellent utility for testing overall system stability. This is the utility Silicon Lottery uses for testing CPU stability.

• Asus RealBench - http://rog.asus.com/rog-pro/realbench-v2-leaderboard/

If you'd like to learn more, then read this: Intel Temperature Guide - http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html

Once again, welcome aboard!

CT