parallel transmission

Definition of parallel transmission in The Network Encyclopedia.

What is parallel transmission (in computer networking)?

A form of signal transmission that sends information 8 or more bits at a time over a cable. Parallel interfaces are used mainly to connect printers, hard drives, and other peripherals to computers.

How It Works

While a serial interface such as RS-232 transfers only 1 bit of data at a time, parallel interfaces typically transfer 8 bits (1 byte) of data at a time. A typical parallel interface for a computer uses a port that accepts a female DB25 connector. The parallel interface for a printer often uses a 36-pin Centronics connector.

For the DB25 connector, all 25 of the leads must be working for parallel transmission to function. In contrast, serial interfaces, which sometimes use DB25 connectors, require only three active leads to transmit data. The parallel 25-pin connector has 17 leads for carrying signals and 8 leads for grounding. Of the 17 leads, 8 are used for data bit signals, 5 for status signals, and 4 for handshaking. Typical throughput of a parallel interface is 16 KBps or 128 Kbps. Parallel communication is usually limited to cables of up to 6 meters, but devices can be used to boost signals for longer distances.


A new type of parallel interface, conforming to the IEEE 1284 standard, supports bidirectional parallel communication at speeds of up to 1 MBps over distances of up to 10 meters. Parallel ports that support this standard are referred to as Enhanced Parallel Ports (EPPs) or Extended Capabilities Ports (ECPs).

See also: