[time-nuts] Windows XP time

Jim King jim at jimking.net
Thu May 18 08:35:46 EDT 2006


Joseph Gray wrote:
>> The fundamental difference between SNTP and NPT is that SNTP does only a
>> period check and adjustment, so the clock can drift significantly
>> between polls.  NTP on the other hand attempts to continuously steer the
>> clock, and uses a much more sophisticated algorithm to determine the
>>     
> offset.
>   
>> John
>>     
>
> I knew SNTP was not as good as NPT, but I would have thought that SNTP kept
> the clock accurate to at least the nearest second. Obviously not. So, what's
> the worst that a typical PC clock would be off when using SNTP?
>   

I've found that when Windows is behaving its SNTP client does a pretty 
good job of keeping the system time within 100ms of an NTP server.  
Here's a screenshot of NTPmonitor showing my office PC's time offset 
overnight:  http://flounder.jimking.net/~jim/files/ntpmonitor-boron.png  
(The red line in the plot is the server that the PC is syncing with.)

At times, I have seen Windows timekeeping get squirrely, and in that 
case I'll see large excursions.  Most of the time it behaves pretty well.

A hint:  For some reason the SNTP client needs/prefers/desires a ",0x1" 
tacked onto the end of the SNTP server name.  e.g. "net time 
/setsntp:us.pool.ntp.org,0x1".  Does anybody know exactly what the 
",0x1" does?

My FreeBSD box with an M12 keeps much better time, of course. :)

Jim





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