Synchronous

Synchronous describes processes that are coordinated in time, typically by a shared clock signal or a common timing reference. The term, from Greek synchronos meaning "occurring at the same time," is used across engineering, computing, and communications to distinguish time-coordinated operations from asynchronous ones, where events occur at irregular intervals without a global timing reference.

In electrical and mechanical engineering, synchronous devices rely on a constant reference frequency. Synchronous machines, such as certain motors and generators, run at a speed determined by the supply frequency and the machine's design; their rotor field must lock to the rotating magnetic field. Synchronous timing is also central to many power grids and coordinated control systems.

In digital electronics and computing, synchronous circuits use a clock to regulate state changes, yielding predictable timing and easier verification, at the cost of power consumption and sensitivity to clock distribution issues. Synchronous data transmission transfers bits aligned to a clock or a separate timing signal, enabling higher data integrity over long distances; examples include SONET/SDH networks. By contrast, asynchronous approaches coordinate events without a shared clock, often using start and stop signals.

In software, synchronous operations execute sequentially and block until completion, while asynchronous operations may run concurrently or be notified upon completion, allowing non-blocking behavior and improved responsiveness.