Synchronization is timekeeping
A timekeeper is an instrument or person that measures the passage of time; in the case of the latter, often with the assistance of a clock or stopwatch...

 which requires the coordination of events to operate a system
System is a set of interacting or interdependent components forming an integrated whole....

 in unison. The familiar conductor
Conducting is the art of directing a musical performance by way of visible gestures. The primary duties of the conductor are to unify performers, set the tempo, execute clear preparations and beats, and to listen critically and shape the sound of the ensemble...

 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.
Some systems may be only approximately synchronized, or plesiochronous
The term Plesiochronous is derived from the Greek plesio, meaning near, and chronos, time, and refers to the fact that plesiochronous systems run in a state where different parts of the system are almost, but not quite perfectly, synchronised....

. For some applications relative offsets between events need to be determined, for others only the order
Partially ordered set
In mathematics, especially order theory, a partially ordered set formalizes and generalizes the intuitive concept of an ordering, sequencing, or arrangement of the elements of a set. A poset consists of a set together with a binary relation that indicates that, for certain pairs of elements in the...

 of the event is important.

Today, synchronization can occur on a global basis due to GPS
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

-enabled timekeeping systems.


Apart from its use for navigation (see John Harrison
John Harrison
John Harrison was a self-educated English clockmaker. He invented the marine chronometer, a long-sought device in solving the problem of establishing the East-West position or longitude of a ship at sea, thus revolutionising and extending the possibility of safe long distance sea travel in the Age...

), synchronization was not important in transportation until the nineteenth century, when the coming of the railways made travel fast enough for the differences in local time between adjacent towns to be noticeable (see

In some territories, sharing of single railroad tracks was controlled by the timetable. Thus strict timekeeping was a safety requirement. To this day, railroads can communicate and signal along their tracks, independently of other systems for safety.


The lessons of timekeeping are part of engineering technology.
In electrical engineering
Electrical engineering
Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical...

 terms, for digital logic and data transfer, a synchronous object requires a clock signal
Clock signal
In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome to coordinate actions of circuits...

Timekeeping technologies such as the GPS
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 satellites and Network time protocol
Network Time Protocol
The Network Time Protocol is a protocol and software implementation for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. Originally designed by David L...

 (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
    Synchronization (computer science)
    In computer science, synchronization refers to one of two distinct but related concepts: synchronization of processes, and synchronization of data. Process synchronization refers to the idea that multiple processes are to join up or handshake at a certain point, so as to reach an agreement or...

     (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 condition
    Race condition
    A race condition or race hazard is a flaw in an electronic system or process whereby the output or result of the process is unexpectedly and critically dependent on the sequence or timing of other events...

  • Cryptography
    Cryptography is the practice and study of techniques for secure communication in the presence of third parties...

  • Multimedia
    Multimedia is media and content that uses a combination of different content forms. The term can be used as a noun or as an adjective describing a medium as having multiple content forms. The term is used in contrast to media which use only rudimentary computer display such as text-only, or...

  • Music
    Music is an art form whose medium is sound and silence. Its common elements are pitch , rhythm , dynamics, and the sonic qualities of timbre and texture...

  • Neuroscience
  • Photography
    Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

  • Physics
    Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

     (The idea of simultaneity
    Simultaneity is the property of two events happening at the same time in at least one frame of reference. The word derives from the Latin simul, at the same time plus the suffix -taneous, abstracted from spontaneous .The noun simult means a supernatural coincidence, two or more divinely...

     has many difficulties, both in practice and theory.)
  • Synthesizers
    Oscillator sync
    Oscillator sync is a feature in some synthesizers with two or more VCOs . One oscillator will restart the period of another oscillator, so that they will have the same base frequency...

  • Telecommunication
    Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...

Synchronization has several subtly distinct sub-concepts:
  • Phase synchronization
    Phase synchronization
    Phase synchronization is the process by which two or more cyclic signals tend to oscillate with a repeating sequence of relative phase angles.Phase synchronisation is usually applied to two waveforms of the same frequency with identical phase angles with each cycle...

  • Rate synchronization
  • Time offset synchronization
  • Time order synchronization

Some uses of synchronization

  • Film synchronization of image and sound in sound film
    Sound film
    A sound film is a motion picture with synchronized sound, or sound technologically coupled to image, as opposed to a silent film. The first known public exhibition of projected sound films took place in Paris in 1900, but decades would pass before sound motion pictures were made commercially...

  • Synchronization is important in fields such as digital telephony
    Digital telephony
    Digital telephony is the use of digital electronics in the provision of digital telephone services and systems. Since the 1960s a digital core network has almost entirely replaced the old analog system, and much of the access network has also been digitized...

    , video
    Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...

     and digital audio
    Digital audio
    Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...

     where streams of sampled data are manipulated.
  • In electric power
    Electric power
    Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

     systems, alternator synchronization
    Alternator synchronization
    The process of connecting an AC generator to other AC generators is known as synchronization and is crucial for the generation of AC electrical power....

     is required when mulitple generators are connected to an electrical grid.
  • Arbiters
    Arbiter (electronics)
    -Asynchronous arbiters:An important form of arbiter is used in asynchronous circuits, to select the order of access to a shared resource among asynchronous requests. Its function is to prevent two operations from occurring at once when they should not...

     are needed in digital electronic systems such as microprocessor
    A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

    s 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
    Metastability in electronics
    Metastability in electronics is the ability of a digital electronic system to persist for an unbounded time in an unstable equilibrium or metastable state....

  • Encryption
    In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...

     systems usually require some synchronization mechanism to ensure that the receiving cipher is decoding the right bits at the right time,,
  • Automotive transmission
    Transmission (mechanics)
    A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...

    s 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 code
    Time code
    A timecode is a sequence of numeric codes generated at regular intervals by a timing system.- Video and film timecode :...

    s are often used as a means of synchronization in film
    A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...

    , video
    Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...

    , and audio
    Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

  • Flash photography
    Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

    , see Flash synchronization
    Flash synchronization
    In a camera, flash synchronization is defined as the firing of a photographic flash coinciding with the shutter admitting light to photographic film or electronic image sensor. It is often shortened to flash sync or flash synch....

See also

  • Asynchrony
    Asynchrony, in the general meaning, is the state of not being synchronized.* Asynchronous learning* Collaborative editing systemsIn specific terms of digital logic and physical layer of communication, an asynchronous process does not require a clock signal, in contrast with synchronous and...

  • Atomic clock
    Atomic clock
    An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...

  • Clock synchronization
    Clock synchronization
    Clock synchronization is a problem from computer science and engineering which deals with the idea that internal clocks of several computers may differ. Even when initially set accurately, real clocks will differ after some amount of time due to clock drift, caused by clocks counting time at...

  • Double-ended synchronization
    Double-ended synchronization
    For two connected exchanges in a communications network, a double-ended synchronization is a synchronization control scheme in which the phase error signals used to control the clock at one telephone exchange are derived by comparison with the phase of the incoming digital signal and the phase of...

  • Einstein synchronization
  • Entrainment
    Entrainment may refer to:* Air entrainment, the intentional creation of tiny air bubbles in concrete* Brainwave entrainment, the practice of entraining one's brainwaves to a desired frequency...

  • Flywheel
    A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

  • Homochronous
    In telecommunication, the term homochronous describes the relationship between two signalssuch that their corresponding significant instants are displaced by a constant interval of time....

  • Kuramoto model
    Kuramoto model
    The Kuramoto model, first proposed by Yoshiki Kuramoto , is a mathematical model used to describe synchronization. More specifically, it is a model for the behavior of a large set of coupled oscillators...

  • Mutual exclusion
    Mutual exclusion
    Mutual exclusion algorithms are used in concurrent programming to avoid the simultaneous use of a common resource, such as a global variable, by pieces of computer code called critical sections. A critical section is a piece of code in which a process or thread accesses a common resource...

  • Neural synchronization
  • Phase-locked loop
    Phase-locked loop
    A phase-locked loop or phase lock loop is a control system that generates an output signal whose phase is related to the phase of an input "reference" signal. It is an electronic circuit consisting of a variable frequency oscillator and a phase detector...

  • Reciprocal socialization
    Reciprocal socialization
    Reciprocal socialization "is a socialization process that is bidirectional; children socialize parents just as parents socialize children". For example, the interaction of mothers and their infants is sometimes symbolized as a dance or dialogue in which following actions of the partners are...

  • Synchronism
    Synchronism is deliberately achieved coincidence in a point of time.In telecommunication the term synchronism has the following meanings:1. The state of being synchronous....

  • Synchronization (alternating current)
    Synchronization (alternating current)
    -Electricity generation:Electricity generation requires the connection of large numbers of alternators in parallel and additional alternators must be switched in when demand rises....

  • Synchronization in telecommunications
    Synchronization in telecommunications
    Many services running on modern digital telecommunications networks require accurate synchronization for correct operation. For example, if switches do not operate with the same clock rates, then slips will occur and degrade performance...

  • Synchronization of chaos
    Synchronization of chaos
    Synchronization of chaos is a phenomenon that may occur when two, or more, chaotic oscillators are coupled, or when a chaotic oscillator drives another chaotic oscillator...

  • Synchronizer
  • Synchronous conferencing
    Synchronous conferencing
    Synchronous conferencing is the formal term used in science, in particular in computer-mediated communication, collaboration and learning, to describe online chat technologies. It has arisen at a time when the term chat had a negative connotation...

  • Time
    Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

  • Timing Synchronization Function (TSF)
    Timing Synchronization Function (TSF)
    Timing Synchronization Function is specified in IEEE 802.11 wireless local area network standard to fulfill timing synchronization among users. A Timing Synchronization Function keeps the timers for all stations in the same Basic Service Set synchronized. All stations shall maintain a local TSF...

  • Time transfer
    Time transfer
    Time transfer is a scheme where multiple sites share a precise reference time. Time transfer solves problems such as astronomical observatories correlating observed flashes or other phenomenon with each other, as well as cell phone towers coordinating handoffs as a phone moves from one cell to...

  • Timecode
  • Tuning fork
    Tuning fork
    A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs formed from a U-shaped bar of elastic metal . It resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object, and emits a pure musical tone after waiting a...

In the field of video and audio engineering:
  • Genlock
    Genlock is a common technique where the video output of one source, or a specific reference signal from a signal generator, is used to synchronize other television picture sources together. The aim in video and digital audio applications is to ensure the coincidence of signals in time at a...

  • Jam sync
    Jam sync
    Jam sync refers to the practice of applying a phase hit to a system to bring it in synchronization with another. The term originates from the use of this technique to replace defective time code on a video tape recording by replacing it with a new time code sequence, which may be an extension of a...

  • Word sync
    Word sync
    Word sync is a technique for synchronizing digital audio signals between high-end professional devices such as CD players, audio I/O cards etc...

In the field of aircraft gun engineering:
  • Interrupter gear
    Interrupter gear
    An interrupter gear is a device used on military aircraft and warships in order to allow them to target opponents without damaging themselves....

Order synchronization and related topics:
  • Rendezvous problem
    Rendezvous problem
    The rendezvous dilemma can be formulated in this way:If they both choose to wait, of course, they will never meet. If they both choose to walk there are chances that they meet and chances that they do not...

  • Interlocking
    In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. The signalling appliances and tracks are sometimes collectively referred to as an interlocking plant...

  • Race condition
    Race condition
    A race condition or race hazard is a flaw in an electronic system or process whereby the output or result of the process is unexpectedly and critically dependent on the sequence or timing of other events...

  • Concurrency control
    Concurrency control
    In information technology and computer science, especially in the fields of computer programming , operating systems , multiprocessors, and databases, concurrency control ensures that correct results for concurrent operations are generated, while getting those results as quickly as possible.Computer...

  • Room synchronization
    Room synchronization
    The room synchronization technique is a form of concurrency control in computer science.The room synchronization problem involves supporting a set of m mutually exclusive "rooms" where any number of users can execute code simultaneously in a shared room , but no two users can simultaneously execute...

  • Transient blocking synchronization
  • Comparison of synchronous and asynchronous signalling
    Comparison of synchronous and asynchronous signalling
    Synchronous and asynchronous transmissions are two different methods of transmission synchronization. Synchronous transmissions are synchronized by an external clock, while asynchronous transmissions are synchronized by special signals along the transmission medium.-The need for...

Compare with:
  • Synchronicity
    Synchronicity is the experience of two or more events that are apparently causally unrelated or unlikely to occur together by chance and that are observed to occur together in a meaningful manner...

    , a mystical notion due to Carl Jung
    Carl Jung
    Carl Gustav Jung was a Swiss psychiatrist and the founder of Analytical Psychology. Jung is considered the first modern psychiatrist to view the human psyche as "by nature religious" and make it the focus of exploration. Jung is one of the best known researchers in the field of dream analysis and...

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