Synchronization

"Synchrony" redirects here. For linguistic synchrony, see Synchronic analysis. For the X-Files episode, see Synchrony (The X-Files).

"Synchronised" redirects here. For the racehorse, see Synchronised (horse).

Synchronization is the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time.

Systems operating with all their parts in synchrony are said to be synchronous or in sync.

Firefighters marching in a parade

Some systems may be only approximately synchronized, or plesiochronous. For some applications relative offsets between events need to be determined, for others only the order of the event is important.

Today, synchronization can occur on a global basis due to GPS-enabled timekeeping systems.

Transport

Time-keeping and synchronization of clocks was a critical problem in long-distance ocean navigation; accurate time is required in conjunction with astronomical observations to determine how far East or West a vessel has traveled. The invention of an accurate marine chronometer revolutionized marine navigation. By the end of the 19th century, time signals in the form of a signal gun, flag, or dropping time ball, were provided at important ports so that mariners could check their chronometers for error.

Synchronization was important in the operation of 19th century railways, these being the first major means of transport fast enough for the differences in local time between adjacent towns to be noticeable. Each line handled the problem by synchronizing all its stations to headquarters as a standard railroad time. In some territories, sharing of single railroad tracks was controlled by the timetable.^{[citation needed]} The need for strict timekeeping led the companies to settle on one standard, and civil authorities eventually abandoned local mean solar time in favor of that standard.

Communication

In electrical engineering terms, for digital logic and data transfer, a synchronous object requires a clock signal. Timekeeping technologies such as the 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.

Synchronization is an important concept in the following fields:

• Computer science (In computer science, especially parallel computing, synchronization refers to the coordination of simultaneous threads or processes to complete a task; in order to obtain correct runtime order and avoid unexpected race conditions.)
• Cryptography
• Multimedia
• Music (Rhythm)
• Neuroscience
• Photography
• Physics (The idea of simultaneity has many difficulties, both in practice and theory.)
• Synthesizers
• Telecommunication

Synchronization has several subtly distinct sub-concepts:

• Phase synchronization
• Frequency synchronization
• Time offset synchronization
• Time order synchronization

Uses

• Film synchronization of image and sound in sound film.
• Synchronization is important in fields such as digital telephony, video and digital audio where streams of sampled data are manipulated.
• In electric power systems, alternator synchronization is required when multiple generators are connected to an electrical grid.
• Arbiters are needed in digital electronic systems such as microprocessors to deal with asynchronous inputs. There are also electronic digital circuits called synchronizers that attempt to perform arbitration in one clock cycle. Synchronizers, unlike arbiters, are prone to failure. (See metastability in electronics).
• Encryption systems usually require some synchronization mechanism to ensure that the receiving cipher is decoding the right bits at the right time.
• Automotive transmissions contain synchronizers which allow the toothed rotating parts (gears and splined shaft) to be brought to the same rotational velocity before engaging the teeth.
• Time codes are often used as a means of synchronization in film, video, and audio applications.
• Flash photography, see Flash synchronization

See also

• Asynchrony
• Atomic clock
• Clock synchronization
• Data synchronization
• Double-ended synchronization
• Einstein synchronization
• Entrainment
• File synchronization
• Flywheel
• Homochronous
• Kuramoto model
• Mutual exclusion
• Neural synchronization
• Phase-locked loops
• Reciprocal socialization
• Synchronism
• Synchronization (alternating current)
• Synchronization in telecommunications
• Synchronization of chaos
• Synchronizer
• Synchronous conferencing
• Time
• Timing Synchronization Function (TSF)
• Time transfer
• Timecode
• Tuning fork

In the field of video and audio engineering:

• Genlock
• Jam sync
• Word sync

In the field of aircraft gun engineering:

• Interrupter gear

Order synchronization and related topics:

• Rendezvous problem
• Interlocking
• Race condition
• Concurrency control
• Room synchronization
• Comparison of synchronous and asynchronous signalling

Compare with:

• Synchronicity, an alternative organizing principle to causality conceived by Carl Jung.