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In general, asynchronous (pronounced ay-SIHN-kro-nuhs, from Greek asyn-, eaning "not
with," and chronos, meaning "time") is an adjective describing objects or events that are
not coordinated in time. In information technology, the term has several different usages.
1) In telecommunication signaling within a network or between networks, an
asynchronous signal is one that is transmitted at a different clock rate than another
signal. (Plesiochronous signals are almost but not quite in synchronization - and a
method is used to adjust them - and synchronous signals are those that run at the same
clock rate.
2) In computer programs, asynchronous operation means that a process operates
independently of other processes, whereas synchronous operation means that the
process runs only as a result of some other process being completed or handing off
operation. A typical activity that might use a synchronous protocol would be a
transmission of files from one point to another. As each transmission is received, a
response is returned indicating success or the need to resend. Each successive
transmission of data requires a response to the previous transmission before a new one
can be initiated.
Synchronous program communication is contrasted with asynchronous program
communication.
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