Editing Time server (section)

{{Short description|Server that reads time information and distributes it}}
[[File:Time_server_Elproma-front_panel.jpg | thumb|right | alt=Black box with green screen and buttons | A typical commercial time server in rackmount form factor. (Elproma front panel).]]
A '''time server''' is a [[server (computing)|server]] [[computer]] that reads the actual time from a [[time signal|reference clock]] and distributes this information to its clients using a [[computer network]]. The time server may be a local network time server or an internet time server.

The most important and widely used protocol for distributing and synchronising time over the Internet is the [[Network Time Protocol]] (NTP), though other less-popular or outdated time protocols continue in use. A variety of protocols are in common use for sending time signals over radio links and serial connections.

The time reference used by a time server could be another time server on the network or the Internet, a connected radio clock or an [[atomic clock]]. The most common true time source is a [[Global Positioning System|GPS]] or [[Radio clock#GPS clocks|GPS master clock]]. Time servers are sometimes multi-purpose [[network server]]s, dedicated network servers, or dedicated devices. All a dedicated time server does is provide accurate time.

An existing network server (e.g. a file server) can become a time server with additional software. The NTP homepage provides a free and widely used reference implementation of the NTP server and client for many popular [[operating system]]s.  The other choice is a dedicated time server device.

The term "stratum" is used to label the closeness to a central or high quality time server. The stratum indicates the place of a particular time server in a hierarchy of servers. The scale is 1 to 15 where 1 is the most accurate and likely a highly specialized physical hardware device. Some time clients will reject a time update from a server whose stratum is too high, and most will prefer low strata time sources to higher ones. This can be a pitfall for administrators setting up an in-house time server with no true time source.