What about Windows 7
We decided to install Windows 7 on Intel to see if you can affect it the same way. By default, the "useplatformclock" parameter is also not present in the BCD, after downclocking from Windows here is what happens:
That's it, we know now what's happening, this screenshot tells us the following:
- The QPC Timer is using the DMI frequency by default, a timer source that is sensitive to bus frequency change.
- The RTC Timer is not using the same source as the QPC on Windows 7.
- The RTC Timer is not sensitive to bus frequency change meaning it uses an external hardware timer such as HPET or ACPI.
What happens if you add the "useplatformclock" parameter to Windows' 7 BCD and set it to Yes:
The QPC is now using the HPET and is not affected by bus frequency change anymore.