1. A specialized processor that comprises an information route and associated
circuitry to control input and/or output operations. It normally provides for
formatting and buffering and has the necessary control to meet the timing
requirements of an I/O device. In an interface that has a number of parallel
channels, each is usually separately dedicated to the passing of a single type
of information such as data.
Several different I/O devices may be connected to one channel and the control
circuitry within the channel directs the data streams to or from the appropriate
device. If the I/O devices have a relatively slow data rate, e.g. line printers,
displays, document readers, then a multiplexer channel is used to connect them
to the processor. The transfers to or from the separate devices are multiplexed,
i.e. interleaved, character by character, such that several devices can work
When a number of devices with high data rates, e.g. magnetic disk and tape,
are to be connected, a selector channel is used. This will transfer a complete
record to or from a device before reselecting. Usually the selection of a device
remains stable for the passage of more than one record. While the selector
channel is dealing with one device, the other devices connected to it cannot
transfer information but they may still be active, e.g. in a search or rewind
A channel is often a wired-program processor. As
channels have become more elaborate they have tended to become programmed
computers (I/O processors) in themselves. See also
2. (transmission channel; communication channel):
A unidirectional information
route in data transmission. See also Shannon's model.
3. A link (physical or virtual) to a host
computer in a communication network.
4. One of the longitudinal rows in which holes may be punched in paper tape.
In addition to its use as a data input/output medium, punched tape was widely
used in vertical format units for controlling the
format of printer output. Although the paper loop has been replaced by binary
information in a memory, the term channel is sometimes still used to refer to
the equivalent electronic signal.