[ntp:questions] Re: ntp servers reporting leap second erroneously?

Martin Burnicki martin.burnicki at meinberg.de
Tue Oct 25 11:36:24 UTC 2005


Hal Murray wrote:
> How fast does Windows normally slew?  I was expecting it to be 500
> ppm which would take a long time to slew a whole second.

Maybe the following is a bit nitpicking, but "Windows" doesn't slew the time
at all.

Whichever time adjustment service is running, it can modify the tick
adjustment value under Windows as required/desired. 

500 ppm is a limitation which is specific to ntpd, and maybe operating
systems which implement the kernel clock algorithm developed by Dave Mills,
which is great, BTW. AFAIK the limitation is with respect to the time
synchronization algorithm and the stability of the control loops.

Windows doesn't implement Dave Mills' clock model, and other time adjustment
services are not limited to the 500 ppm value.

The article I was referring to can also be found in the NTP questions
mailing list archive:

In the log output you can see that the tick adjustment value is temporarily
changed from 156250 to 78125, so the system time temporarily increases with
half speed only until the time offset introduced by the leap second has
been compensated.

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

More information about the questions mailing list