Isochronous : From Greek iso, equal + chronos
In Greek mythology, Chronos in pre-Socratic philosophical works is said to be the personification of time. His name in Greek means "time" and is alternatively spelled Chronus or Khronos.Chronos was imagined as an incorporeal god, serpentine in form, with three heads—those of a man, a bull, and...

, time. It literally means regularly, or at equal time intervals. In general English language, it refers to something that occurs at a regular interval, of the same duration; as opposed to synchronous which refers to more than one thing happening at the same time. The term is used in different technical contexts, but often refers to the primary subject maintaining a certain interval, despite variations in other measurable factors in the same system.
  • In horology
    Horology is the art or science of measuring time. Clocks, watches, clockwork, sundials, clepsydras, timers, time recorders and marine chronometers are all examples of instruments used to measure time.People interested in horology are called horologists...

    , isochronous refers to the timekeeping principle of pendulum
    A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...

    s noted by Galileo in the late 16th century. He observed that the oscillation
    Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

     period of a pendulum is constant, regardless of the angle of the swing.
  • In 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...

    , isochronous has the following meanings:
  1. Of a periodic signal, pertaining to transmission
    Transmission (telecommunications)
    Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...

     in which the 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....

     interval separating any two corresponding transitions is equal to the unit interval
    Unit interval
    In mathematics, the unit interval is the closed interval , that is, the set of all real numbers that are greater than or equal to 0 and less than or equal to 1...

     or to a multiple of the unit interval; but phase is arbitrary (and in some systems may change slowly over time)
  2. Pertaining to data transmission
    Data transmission
    Data transmission, digital transmission, or digital communications is the physical transfer of data over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibres, wireless communication channels, and storage media...

     in which corresponding significant instants of two or more sequential signals have a constant phase
    Phase (waves)
    Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...

    • In power generation
      Electricity generation
      Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

      , isochronous means that the frequency of the electricity generated is 'flat' or constant, and there is zero generator droop.
    • In the Universal Serial Bus
      Universal Serial Bus
      USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....

       used in computer
      A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

      s, isochronous is one of the four data flow types for USB devices (the others being Control, Interrupt and Bulk). It is commonly used for streaming data types such as video or audio sources. Similarly, in the IEEE 1394 interface
      IEEE 1394 interface
      The IEEE 1394 interface is a serial bus interface standard for high-speed communications and isochronous real-time data transfer, frequently used by personal computers, as well as in digital audio, digital video, automotive, and aeronautics applications. The interface is also known by the brand...

       standard commonly called Firewire, includes support for isochronous streams of audio and video at known constant rates.
    • In dynamical system theory
      Dynamical system
      A dynamical system is a concept in mathematics where a fixed rule describes the time dependence of a point in a geometrical space. Examples include the mathematical models that describe the swinging of a clock pendulum, the flow of water in a pipe, and the number of fish each springtime in a...

       an oscillator is called isochronous if the frequency is independent of its amplitude. For instance, in horology
      Horology is the art or science of measuring time. Clocks, watches, clockwork, sundials, clepsydras, timers, time recorders and marine chronometers are all examples of instruments used to measure time.People interested in horology are called horologists...

      , isochronous refers to a mechanical clock or watch
      A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...

       which runs at the same rate regardless of changes in its drive force, so it keeps correct time as the mainspring
      A mainspring is a spiral torsion spring of metal ribbon that is the power source in mechanical watches and some clocks. Winding the timepiece, by turning a knob or key, stores energy in the mainspring by twisting the spiral tighter. The force of the mainspring then turns the clock's wheels as it...

    • In particle accelerator
      Particle accelerator
      A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...

      s an isochronous cyclotron
      Isochronous cyclotron
      In particle accelerators an Isochronous cyclotron is a cyclotron that maintains a constant RF driving frequency, and compensates for the relativistic mass gain of the accelerated particles by alternating field gradient in space but constant in time...

       is a cyclotron where the field strength increases with radius to compensate for relativistic increase in mass with speed

Closely related to the property of being isochronous is the term isochrone referring to contour line
Contour line
A contour line of a function of two variables is a curve along which the function has a constant value. In cartography, a contour line joins points of equal elevation above a given level, such as mean sea level...

s of equal time, for instance, in geological layers
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

, tree rings
Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year...

 or wave fronts.
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