Guys,
Since Ambient temperature, hardware configurations and stress test software are major variables, in order to compare apples to apples it's important to be specific. “Load” or “full load” are misleading user terms that could mean
anything. Gaming, applications, rendering, transcoding and streaming are partial,
fluctuating workloads with
fluctuating temperatures, which aren’t well suited for testing thermal performance.
Not all loads are created equal. “Stress” tests vary widely and can be characterized into two categories;
stability tests which are
fluctuating workloads, and
thermal tests which are
steady workloads.
As per the Datasheets, Intel tests their processors at a steady 100% TDP workload 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.
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 six processor Generations at stock settings rounded to the nearest 5%:
Higher TDP tests produce higher Core temperatures. All tests will show 100% CPU
Utilization in Windows Task Manager, which indicates processor resource activity,
not % TDP
workload. Although actual Power dissipation (Watts) varies with Core Speed, Core voltage and workload, Prime95 v26.6 Small FFT’s always provides a true and steady 100% workload, whether you’re running stock or overclocked.
Note: 2nd and 3rd Generation i7, i5 and i3 CPU’s have AVX (Advanced Vector Extension) Instruction Sets, while 4th through 9th Generation i9, i7, i5 and i3 CPU’s have
AVX2 Instruction Sets. Prime95 versions
later than 26.6 run AVX codes on the CPU's Floating Point Unit (FPU). 2nd and 3rd Generation CPU’s are minimally affected by AVX, but 4th through 9th Generation with
AVX2 may experience
unrealistic temperatures
up to 20°C higher.
Many 6th through 9th Generation motherboards address the AVX problem by providing offset adjustments (downclock) in BIOS. -3 (300 MHz) or more may be needed to limit Core temperatures to 85°C. Since 4th and 5th Generation don’t have AVX offsets, you can create a BIOS Profile for gaming, and a downclock Profile for AVX apps such as rendering or transcoding. If you’re overclocked, you may also need to upgrade your CPU cooler and case fans.
AVX codes 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 codes don't affect Core i 1st Generation, Core 2, Pentium or Celeron processors since they don't have AVX/2 Instruction Sets.
As per Intel’s Datasheets, TDP and Thermal Specifications are validated “without AVX”.
Stability tests such as OCCT have cycles that exceed 120% workload, which isn’t well suited for testing CPU thermal performance. However, OCCT will by default, terminate the CPU tests at 85°C.
Shown above from left to right: Small FFT's, Blend, Linpack and IntelBurn Test.
Note the
steady thermal signature of Small FFT's, which allows accurate measurements of Core temperatures.
A steady 100% workload is key for thermal testing so the CPU, cooler, socket, motherboard and voltage regulators can thermally stabilize.
Shown above from left to right: Small FFT's, Intel Extreme Tuning Utility CPU Test, and AIDA64 CPU Test.
Intel Extreme Tuning Utility is yet another fluctuating workload, which isn't very well suited for thermal testing. AIDA64 has
15 possible stress test selections which yield 15 different Core temperatures. Although the individual CPU test is a steady workload, it's just 70% TDP, which isn't well suited for thermal testing. Only the CPU/FPU test combination is about 100% TDP workload. All other AIDA64 test selections are fluctuating workloads, which again aren't well suited for thermal testing.
• Prime95 v26.6 -
http://www.mersenneforum.org/showthread.php?t=15504
You might want to read this Sticky:
Intel Temperature Guide -
http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html
CT
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