Windows 8 RTC Bug Affects Intel Platform Benchmark Results

The folks at HWBOT have discovered a flaw in Windows 8 real-time clock (RTC) implementation that affect how the operating system’s sense of time. According to the site, “Microsoft made changes to how it measures time to be compatible with embedded or low cost PCs that do not have a fixed RTC clock.”

How does this affect the benchmark results? Well, the HWBOT team has tested system running at same 4.16GHz speed with two different configurations: 130 MHz BCLK x 32 CPU ratio and 122 MHz BCLK x 34x CPU ratio. The results is that the system with 122MHz BCLK yield 1 to 7% improvement in performance across various benchmarks that include Wprime32M, Prime95, Heaen, SuperPi, PiFast, Aquamark3, and 3DMark. As it appears, lowering the BCLK speed has essentially slowed down Windows sense of time. In one test where the team downclock the base clock by 6%, they observed Windows running behind 18 seconds after 5 minutes.

The issue at the moment appears to only affecting Intel platform dating back to LGA775 socket and not on any of the AMD AM3+ or APU platform based on the testing done from ocholics. 

As PC benchmark scores are a measure of performance over a period of time. When accuracy of timing is in question, the result won’t be useful to for comparison purpose. While this does not mean that you should not use any of the benchmarks to test your system. However, you should keep in mind that the score you obtained may be affected due to the timing issue if you modified the base clock as it appears that modifying the multiplier seems unaffected the result.