How does a computer know the time and date? How does it know when the clocks are next due to go forward or back? Or when there will next be 61 seconds in the minute?
A computer time-stamps every event, such as an email being sent or a file saved, by taking the time from its internal clock. This clock is usually an inexpensive quartz oscillator that can drift by several seconds over a day and gradually builds up an error of many minutes. If the computer is to tell the time accurately it must set its internal clock regularly against a trusted external source of time, which must be both accurate and reliable.
NPL's Internet Time Service (ITS) allows a computer to set its internal clock by connecting over the Internet to a server at NPL that transmits a time code using the well-established Network Time Protocol (NTP). A user guide to the NPL Internet Time Service provides more information and explains how to obtain and install software that will allow a computer to use the service.
Downloaded the user guide here
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