David J Taylor wrote: > Hal Murray wrote: > >>>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. > > > For NTP, Windows uses one of the CPU clocks (I forget now if it's RDTSC or > the Performance Counter) to interpolate between the Windows ticks (which > are at 10 - 15ms intervals). That's why I asked the OP to try the simple > test of disabling the "spread-spectrum" in the BIOS - to see if it did > make a difference. >
It's currently using the Performance Counter. Danny _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
