There's a problem with Windows 8's real-time clock that affects all benchmarking tools.
HWBOT said on Monday that it is no longer accepting Windows 8 benchmark records due to, according to the site, severe validity problems with the Windows 8 real time clock (RTC). All existing Windows 8 benchmarks will be disqualified as well as new ones submitted to the popular benchmarking database.
The real-time clock is typically on a hardware level, residing in the motherboard's southbridge and feeding off a button battery just in case something happens to the power. Thus unlike software clocks which can be easily changed manually or altered by other software, this one silently keeps track of the proper time, even when the computer is shut down. Benchmark tools typically rely on this hardware clock to report exactly when the benchmark started and finished.
However for Windows 8, the platform features a real-time clock that accommodates embedded or low-cost devices that do not have a hardware-based clock, thus its timekeeping routines are a little different thanks to the platform's "one OS to rule them all" scenario. The site doesn't go into detailed specifics, but instead reports that when the CPU base clock (BCLK) frequency in software is changed (not at boot), it has a huge effect on Windows 8's ability to keep proper time.
As an example, the site used a Haswell test system and downclocked the BCLK frequency by about 6 percent from 130 MHz to 122 MHz. Using a CPU ratio of respectively 32x and 34x, the resulting CPU frequency remained 4160 MHz. Eventually it was determined that Windows 8 had actually lost 18 seconds over a five minute period; when overclocked, Windows 8 was 18 seconds quicker. Overclock roughly 4 percent, and after two minutes, Windows Time was three seconds ahead of real time.
"At the moment of writing, we do not have the full technical what’s and how’s figured out," the site states. "Since this problem affects everyone who is passionate about overclocking, it is important to provide an explanation. It is far from the complete story, but it should be enough for you to understand why we have decided to ban Windows 8 from HWBOT."
Having a device's timer line up with the real world time ensures that applications such as benchmarks and even alarm clocks produce accurate measurements, predictions and results. Benchmarks assume that the local RTC is accurate and functioning correctly. As it stands now, running a five-minute benchmark on an underclocked Windows 8 device means the process will actually take five minutes and eighteen seconds, or six percent longer. Boost the multiplier to compensate for the lower BCLK, and the device draws 6 percent more frames, or completes six percent more floating point calculations, thus generating a 6 percent higher score.
"It is not possible for HWBOT to accept any benchmark results or records achieved using Windows 8," the site states. "Simply no benchmark – not even 3DMark – is unaffected by Microsoft’s RTC design decisions. As a result, it is impossible to verify the veracity of a system performance indicative in Windows 8. The resulting score of any benchmark is relative to the RTC bias of that system."
For now, HWBOT will block any seemingly out-of-line Windows 8-based benchmark results. It will also block any Windows8-based benchmark record, even if the score seems in line with the expectations. For more information, read the full report here.