razzledazzler,
On behalf of Tom's Hardware Moderator Team, welcome aboard!
With Vcore set at 1.265 in BIOS, a Vdroop value in Windows from 1.264 to 1.248 is only 16 millivolts (0.016 volts), which is actually quite good. Even though Vcore settings in BIOS are typically commanded in 5mv increments, each 8mv step equals 1 bit, so 16mv equals 2 bits. In contrast, with 4th Generation processors such as the i7-4790K, the VRM was integrated into the Package ("Fully Integrated Voltage Regulator" or "FIVR"), so voltage regulation was very tight, and typically was within 1 bit, which is only 8mv. Essentially, what you set was what you get.
Voltage droop or voltage "sag" is normal and expected due to momentary "inrush current" which occurs whenever workload suddenly increases. However, although LLC is designed to compensate for Vdroop, the ideal setting will
slightly undershoot (but
not overshoot) your BIOS setting during the heaviest workloads, whereas excessive Vdroop can cause instabilities and BSODs.
For comparison:
Good - 8 or 16 mv
Fair - 24 or 32 mv
Poor - 40 or 48 mv
RMA - 56 or > mv
Moreover, Vcore is most likely to fluctuate with workloads which fluctuate.
“Stress” tests vary widely and can be characterized into two categories;
stability tests which are
fluctuating workloads, and
thermal tests which are
steady workloads. Prime95 Small FFTs
(AVX disabled) is ideally suited for testing thermal performance, because it conforms to Intel's Datasheets as a
steady 100% workload with
steady Core temperatures. No other non-proprietary utility can so closely replicate Intel's thermal test workload.
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 Intel settings rounded to the nearest 5%:
Although these tests range from
70% to 130% TDP workload, Windows Task Manager interprets every test as
100% CPU Utilization, which is processor resource activity,
not actual %TDP workload.
Core temperatures respond directly to Power consumption (Watts), which is driven by workload. Prime95 Small FFTs
(AVX disabled) provides the correct workload for testing thermal performance. If Core temperatures don't exceed
80°C, your CPU should run the most demanding
real-world workloads without overheating.
Although "Throttle" temperature for your 8700K is 100°C, the consensus among well informed and highly experienced reviewers, system builders and expert overclockers, is that it's prudent to observe a reasonable thermal margin below Throttle temperature for ultimate stability, performance and longevity. So regardless of environmental conditions, hardware configurations, software workloads or any other variables,
Core temperatures above 85°C are not recommended.
Here's the nominal operating range for Core temperature:
Core temperatures below 80°C are ideal.
For everyone's benefit, we'll also point out that Core temperatures, as well as all computer temperatures, increase and decrease with ambient (room) temperature, for which the International Standard for "normal" is 22°C of 72°F. So for every degree above normal your ambient temperature is, so will be your Core temperatures.
Concerning Prime95, regardless of the version, Small FFTs is a
steady-state 100% workload which has
steady Power consumption (Watts) and
steady Core temperatures. Although version 26.6 does not have AVX Instruction Sets, later versions such as 30.3 allow all AVX test selections to be disabled.
As per Intel’s Datasheets, TDP and Thermal Specifications are validated “without AVX”.
Prime95 with AVX test selections
enabled will impose a
brutal and
unrealistic 130% workload which can
increase Core temperatures by up to 20°C. Therefore, version 26.6 or later versions with
all AVX test selections disabled provide the correct workload for testing
thermal performance when using the Small FFTs test, due to its
steady-state 100% workload, which is also useful for observing Vdroop and Vcore stability.
As you have also noted, AIDA64 causes Vdroop fluctuations. However, to put it into perspective, let's keep in mind that testing
thermal performance differs from testing
stability; thus the term "System Stability Test" in AIDA64. When commenting about AIDA64, users seldom make any distinctions concerning
which test selections they ran.
AIDA64 has 4 CPU related stress test selections (CPU, FPU, Cache, Memory) which have
15 possible combinations that yield
15 different workloads and
15 different Core temperatures. The individual FPU test is about 115% workload, the CPU/FPU combination is about 90%, all 4 tests combined is about 80% and the individual CPU test is only about 70%. All other AIDA64 test selections are fluctuating workloads which are suitable for
stability testing, but not for
thermal testing or analyzing Vdroop.
If you'd like to learn more, then just click on the link in my signature.
Once again, welcome aboard!
CT