Synchronization

Synchronization is coordination with respect to time. It is an important concept in the following fields:

Synchronization has several subtly distinct sub-concepts:

Rate synchronization
Phase synchronization
Time offset synchronization
Time order synchronization

Two different time sequences may be synchronized in one sense without being synchronised in another, or synchronised at one time scale whilst being asynchronous in another.

Systems operating with all their parts in synchrony are said to be synchronous. Some systems may be only approximately synchronised, or plesiochronous.

For some applications relative offsets between events need to be determined, for others only the order of the event is important. The idea of simultaneity has many difficulties, both in practice and theory.

Some uses of synchronization:

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.
Synchronizers are needed in digital electronic systems such as microprocessors to deal with asynchronous inputs without generating metastable statess.
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.
Synchronization is also important in industrial automation applications.
Time codes are often used as a means of synchronization.
Technologies such as GPS and NTP provide real-time access to a close approximation to the UTC timescale, and are used for many terrestrial synchronization applications.
Flash photography, see Flash synchronization

Whilst well-designed time synchronization is an important tool for creating reliable systems, excessive use of synchronization where it is not necessary can make systems less fault-tolerant, and hence less reliable.