[ntp:questions] Re: Windows timekeeping - sudden degradation - why?

David J Taylor david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk.invalid
Thu Dec 8 15:23:30 UTC 2005

Just doing a little more work on this.  I wrote a program to display 
(approximately) the resolution of the timer (from a timeGetTime) call, and 
got the following results:

- QuickTime Player running (not even playing a video), timer resolution 
just under 1ms (about 960 us)

- QuickTime not running, timer resolution seems to step between 15.6ms 
(approx) and 10.5ms.

Now these are early results, and my program isn't highly accurate, but it 
suggests that the program may not /only/ be the multimedia timer running 
or not (or is it more accurate to say without the system timer being 
forced into a higher precision?), but also that something is changing the 
basic system clock from a 10ms set to a 15ms step?  I do recall that there 
are a number of different basic clock periods in Windows, different for NT 
4.0, 2000 workstation and server, and XP.  Each are either (about) 10ms or 

So when Windows XP SP2 was installed, everyone agreed on one system clock 
"frequency" (or should I say timer interrupt frequency), hence the 
stability of that system.  Now I have two system components or application 
software arguing over whether the correct value is 10ms or 15ms.  Is this 
really likely?

Anyone for or against that?  Any idea of which program might be doing 
this?  Perhaps it's just my code, and the 10/15ms switching isn't actually 
happening at all!


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