[ntp:questions] NTP and WinXP

Dave Hart hart at ntp.org
Wed Nov 9 14:11:39 UTC 2011

On Tue, Nov 8, 2011 at 17:52,  <lelonga at free.fr> wrote:
> I'm trying to configure the ntp client (w32time) of a computer that
> runs XP to synchronize with a ntp server running on a linux server.


The Windows Time Service in Windows XP and Windows Server 2003 are
essentially the same, ignoring that XP can't be a domain controller.
If you want better synchronization, ntpd versions 4.2.6 and later can
synchronize your Windows clock to 100 usec or better offset from a LAN
source.  Start by installing ntpd 4.2.4 from http://www.meinberg.de,
which will get you within a handful of milliseconds, then replace the
binaries with newer ones from http://davehart.net/ntp/win/x86/
Applications will still see a clock stepping every 10 or 15 msec, but
that low-resolution clock will in fact be syncrhonized to a higher
precision thanks to ntpd's interpolation on top of the Windows clock.

I wish the story were so simple with Windows Vista and later releases
of Windows, which often challenge the interpolation in ntpd by having
a clock stepping every 0.5 or 1 msec with a scheduling precision of 1
msec, fouling the interpolation approach used by ntpd.  There is room
for improvement in ntpd, but at the cost of spinning (eating massive
CPU) to detect the correlation between the system clock and the
high-resolution counter (performance counter).  With luck, ntpd will
detect the situation and disable interpolation, synchronizing the
clock within a handful of milliseconds.

Dave Hart

Dave Hart

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