The Importance Staying On Time
As with any clock, the clock on your computer can both gain and lose time compared to a reference time. This can make problem tracking difficult, as a user may report a problem at a given time but the clock on your server is a number of minutes out, making the correct time in the log files difficult to find.
Fortunately, the network time protocol (NPT) was devised to solve this problem. This protocol allows a networked computer to request the correct time from another computer and update its own clock automatically. The network makes use of reference clocks such as atomic clocks and radio clocks to set servers to a very accurate time. The network then spans out from that in layers, with one layer of servers accessing these master servers directly, another layer of servers than using the previous ones for their time reference. Groups of servers are organized into pools to ensure that no individual server can become a single point of failure for users.