Windows 10 Affected By Same Downclock Bug Like Windows 8/8.1, Disallowed For Now

Microsoft recently released a Technical Preview of its upcoming Windows 10 operating system. We had a quick look at the operating system to find out it still has the same underclocking bug as their previous two operating systems. The benchmark veracity is in other words still compromised and there is currently no other option than to disallow Windows (10) Technical Preview for submissions at HWBOT.

To recap the problem, here's an excerpt from our Windows 8 article:

“The concept of ‘time’ on a PC configuration is, if not synced via network or internet, an arbitrarily defined constant designed to ensure that the configuration is running in sync with the real world. In other words: hardware and software engineers ensure that ‘one second’ on your PC equals ‘one second’ in real time. One of the reasons why it’s so important to have the PC’s timer line up with the real world time is to ensure that your PC can produce accurate measurements and predictions.” The points we brought up in that editorial are relevant again. To ensure that the arbitrarily defined constant of ‘time’ is the same on everyone’s benchmark system, we rely on the OS and hardware. This worked quite well, until Windows8 came around.

The problem builds on the problems we faced with Heaven. When downclocking the system under Windows8, the Windows RTC is affected as well. The biggest difference between Windows7 and Windows8 is that now all benchmarks (no exception) are affected.

Let us make this more practical. On our Haswell test system we downclocked the BCLK frequency by about 6% from 130 MHz to 122MHz. Using a CPU ratio of respectively 32x and 34x, the resulting CPU frequency remains 4160MHz. Then we ran comparison benchmarks.

We ran a quick test to verify the problems using SuperPI 1M. Below you can find a table with the information.

BCLK frequencyCPU RatioOperating FrequencyBenchmark score
100 MHz40x4000 MHz9.079 sec (reference)
102.5 MHz39x4000 MHz9.282 sec
97.56 MHz41x4000 MHz8.870 sec

As you can see from the above table, lowering the BCLK frequency while maintain the same operating frequency results in a "faster" benchmark time. Increasing the BCLK frequency while maintaining the same operating frequency results in a "slower" benchmark time. This is identical to the behavior we are seeing in Windows 8 and Windows 8.1.

For reference we also made a video showing that the system timer is running out of sync. For this video we underclocked the base clock frequency from 100 MHz to 98 MHz. After 8 minutes and 50 seconds, the system is lagging behind about 8 seconds.

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