Parallel port

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Like the serial interface, a parallel interface is a concept with many implementations.

The de-facto standard parallel port has a DB-25 connector (same but opposite gender of RS-232 serial port), but using only 8 parallel lines for data. The rest are for ground, +5V power and control lines. Even though it has had many uses, it has mainly been used to connect a printer (with a Centronics port in the other end), and is therefore often called a printer port. This port was standardised as IEEE 1284 first in the late 1990s when it started being phased out in favour of USB.

Most platforms have had a DB-25 parallel port, if not as standard often as a common accessory. Platforms include the IBM PC, Apple II, Commodore Amiga, Atari ST and most Unix workstations. Classic Apple Macintosh however, never had it because it used a serial interface to printers before USB.

IBM PC

On PC's, the port was called LPT (line printer). Even though the port has disappeared over time, many desktop PCs still have a socket for it on the motherboard for connecting an optional I/O bracket with a DB-25 port.

Digital joysticks

It was never intended for input devices, but it was sometimes used for it:

Digital joystick adapter.

Especially the Atari standard. One or two joysticks. Some games for Commodore Amiga and Atari ST used the port. Linux has kernel support for several types on the parallel port, with adaptor.