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

Hal Murray hmurray at suespammers.org
Thu Dec 15 08:20:31 UTC 2005

>I would have though that "spread spectrum" (implying a continually 
>changing random frequency) was definitely something to avoid for accurate 
>timekeeping!  As you say, changing the HAL is not something to be 
>undertaken lightly.

Is "spread spectrym" as used for CPU clocks really going to
do anything evil to timekeeping?  Is it really random?  I've been
assuming it was some simple modulation pattern - sine or sawtooth.
It's all on one chip in a cutthroat business so they aren't going
to pay much for it.

What does Windows use for timekeeping?

Linux (on most boxes) uses the interrupts from the TOY/battery-backed
clock, usually running off a 32 KHz watch crystal.  I got surprised
by this a few years ago.  The main complication with using the main
CPU clock is SMP systems.

It's fairly easy to compare the two crystals.  Both track temperature
very well.

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