Network Time Protocol
The Network Time Protocol is a service by which servers, workstations, and other computing devices can maintain synchronised system clocks. It is particularly important for network servers to maintain accurate clocks for the correct scheduling of jobs, coordinating tasks between computers, and for the accurate logging of events, such as user login and logout times, file transfers, web site access, or when mail is sent or received.
Computer clocks can drift over time, much like any other mechanical clock or watch, therefore system administrators should install and configure NTP software on their systems in order to maintain the accuracy of those clocks. To help with the synchronisation, there are freely available public time servers from the NTP Pool Project, universities, and government organisations scattered around the globe. These public time servers themselves consult and coordinate with a restricted set of time servers that are connected to atomic clocks.
As of Windows 2000 and Windows XP, Microsoft Windows comes supplied with NTP software and a short list of time servers. Time servers from the supplied list can be selected or other time servers from ntp.org's lists can be used instead.
For cell phones, many cell network services provide time synchronisation, which can be enabled in the phone's time and date settings.