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Synchronization was important in the operation of 19th-century railways, these being the first major means of transport fast enough for differences in [[local mean time]] between nearby towns to be noticeable. Each line handled the problem by synchronizing all its stations to headquarters as a standard [[railway time]]. In some territories, companies shared a single railroad track and needed to avoid collisions. The need for strict timekeeping led the companies to settle on one standard, and civil authorities eventually abandoned local mean time in favor of railway time.
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== Communication ==
{{further|Synchronization in telecommunications}}
In [[electrical engineering]] terms, for digital logic and data transfer, a [[synchronous circuit]] requires a [[clock signal]]. A clock signal simply signals the start or end of some time period, often measured in microseconds or nanoseconds, that has an arbitrary relationship to any other system of measurement of the passage of minutes, hours, and days.
In a different sense, electronic systems are sometimes synchronized to make events at points far apart appear simultaneous or near-simultaneous from a certain perspective.{{efn|Albert Einstein proved in 1905 in his first relativity paper that there actually are no such things as absolutely simultaneous events.}} Timekeeping technologies such as the [[Global Positioning System|GPS]] satellites and [[Network Time Protocol]] (NTP) provide real-time access to a close approximation to the [[UTC]] timescale and are used for many terrestrial synchronization applications of this kind.
In [[computer science]] (especially [[parallel computing]]), synchronization is the coordination of simultaneous [[thread (computing)|threads]] or [[Process (computing)|processes]] to complete a task with correct runtime order and no unexpected [[race condition]]s; see [[synchronization (computer science)]] for details.
Synchronization is also an important concept in the following fields:
* [[Cryptography]]
* [[Lip sync]]
* [[Multimedia]]
* [[Rhythm]]
* [[Neural synchronization|Neuroscience]]
* Photography
* [[Physics]] (The idea of [[Relativity of simultaneity|simultaneity]] has many difficulties, both in practice and theory.)
* [[Oscillator sync|Synthesizers]]
* Telecommunication
** [[Frame synchronization]]
** [[Synchronization (video)]]
== Dynamical systems ==
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