[ntp:questions] Quick sync between two computers not connected to the internet
Richard B. Gilbert
rgilbert88 at comcast.net
Sat Mar 20 17:06:38 UTC 2010
> I'm trying to sync the time on 2 Windows XP computers that are not on
> the internet and never will be. For testing purposes, they need to
> have the same time. The time does not need to be accurate. What's the
> simplest way to sync these computers?
> I've done a lot of searching, but can't seem to find much about
> computers not attached to the internet.
> I've tried net time \\computer_ip /set /yes, but I get an access
> denied error.
> Thanks in advance.
How close do the two clocks have to be? It's fairly easy to get two
computers to agree within five or ten seconds with no special equipment
or software required. If you need to be within five or ten milliseconds
it starts getting difficult and possibly expensive. If you need to be
within five or ten microseconds it can still be done but it will take
some fairly expensive equipment.
The easiest thing to do if you can site an antenna where it will have an
unobstructed view of the sky, is to purchase a "hardware reference
clock". The cheapest goes for about $100 US. It's called a GPS18-LVC
if memory serves me. If my memory fails me I'm sure someone will be
delighted to point it out! ;-)
The GPS18-LVC and other similar devices, get time from the NAVSTAR (GPS)
satellites. The antenna is generally smaller than a hockey puck. I
have mine on top of a "Leaf Guard" rain gutter. They have a Pulse Per
Second (PPS) output. One edge of the pulse is generally within 50
nanoseconds of the true time. There is also an RS232C serial output
that tells you which second the pulse is marking.
NTPD has drivers for a number of different devices. In addition to GPS
satellites there are VLF and HF broadcasts provided by the National
Institute of Standards and Technology (NIST) in the US. Other countries
also provide radio time signals.
More information about the questions