Parallel port

"LPT" redirects here. For other uses, see LPT (disambiguation).
"Printer port" redirects here. For other uses, see Printer port (disambiguation).
This article is about the Centronics style port. For the concept in general, see Parallel communications.
Parallel port
A DB-25 connector often used for a parallel printer port on IBM PC compatible computers, with the printer icon.
Type Point-to-point
Production history
Designer Centronics, IBM
Designed 1970–1981
Manufacturer Centronics, Dataproducts, Intel, IBM, Compaq, Nortel, etc
General specifications
Length 2.3 cm (0.91 in)
Hot pluggable Usually not
External Yes
Cable Usually up to 25 wires including ground; optionally shielded
Pins 8 data, 4 output control, 5 input control, 8 ground
Connector DB-25, DB25F, "Centronics" 36-pin Amphenol, DC-37, others
Electrical
Signal 0 to +5.0 volt DC
Earth Dedicated pins
Max. voltage 5 volts DC
Data
Data signal Parallel
Width Variable
Bitrate PP: 150 kB/s,[1]
EPP: 2 MB/s
ECP: 2.5 MB/s
Max. devices 2
Protocol Application dependent
Pinout
IBM PC-compatible parallel port pinout
Micro ribbon 36-pin female, such as on printers and on some computers, particularly industrial equipment and early (pre-1980s) personal computers.
Mini-Centronics 36-pin male connector (top) with Micro ribbon 36-pin male Centronics connector (bottom)
The Apple II Parallel Printer Port connected to the printer via a folded ribbon cable; one end connected to the connector at the top of the card, and the other end had a 36-pin Centronics connector.

In computing, a parallel port is a type of interface found on early computers (personal and otherwise) for connecting peripherals. The name refers to the way the data is sent; parallel ports send multiple bits of data at once (parallel communication), as opposed to serial communication, in which bits are sent one at a time. To do this, parallel ports require multiple data lines in their cables and port connectors and tend to be larger than contemporary serial ports, which only require one data line.

There are many types of parallel ports, but the term has become most closely associated with the printer port or Centronics port found on most personal computers from the 1970s through the 2000s. It was an industry de facto standard for many years, and was finally standardized as IEEE 1284 in the late 1990s, which defined the Enhanced Parallel Port (EPP) and Extended Capability Port (ECP) bi-directional versions. Today, the parallel port interface is virtually non-existent in new computers because of the rise of Universal Serial Bus (USB) devices, along with network printing using Ethernet and Wi-Fi connected printers.

The parallel port interface was originally known as the Parallel Printer Adapter on IBM PC-compatible computers. It was primarily designed to operate printers that used IBM's eight-bit extended ASCII character set to print text, but could also be used to adapt other peripherals. Graphical printers, along with a host of other devices, have been designed to communicate with the system.

  1. ^ James, Kevin. PC interfacing and data acquisition : techniques for measurement, instrumentation and control. Oxford; Boston : Newnes, 2000. ISBN 9780750646246. p. 256