[ntp:questions] Re: clock resolutions for different OS

David J Taylor david-taylor at blueyonder.co.uk
Tue Aug 19 20:02:29 UTC 2003


"Drk Ryan" <ryandrk at hotmail.com> wrote in message
news:de98eac0.0308191107.b6e68be at posting.google.com...
> Since operating systems such as Linux, Solaris, certain versions of
> Unix, and WinNT all run at 100Hz clock resolution how is it that their
> timimg suppport varies: FreeBSD handles nanoseconds, Linux handles
> microseconds and WinNT only ~10 milliseconds?
>
> As 1/100Hz = 10ms should they all not return a resolution of 10ms?

10msec is the granularity with which timer events are called for
scheduling etc.  The number of actual (e.g. 1MHz) clock cycles which must
be counted for that timer tick to occur can be varied from the nominal
10000 value in small amounts (e.g. 9990..10010) to make the time interrupt
occur at more correct 10msec intervals.  The interaction of the OS with
the timer tick interrupt, and the actual countdown timer will determine
the precision with which it chooses to report time to its clients.

Cheers,
David





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