Parallel port

Parallel port

A parallel port is a type of interface found on computers (personal and otherwise) for connecting various peripherals. It is also known as a printer port or Centronics port. The IEEE 1284 standard defines the bi-directional version of the port.


The Centronics Model 101 printer was introduced in 1970 and included the first parallel interface for printers.cite book |author=Webster, Edward C. |title=Print Unchained: Fifty Years of Digital Printing: A Saga of Invention and Enterprise |publisher=DRA of Vermont |location=West Dover, VT |year=2000 |isbn=0-9702617-0-5] The interface was developed by Dr. An Wang, Robert Howard and Prentice Robinson at Wang Laboratories. The now-familiar connector was selected because Wang had a surplus stock of 20,000 Amphenol 36-pin micro ribbon connectors that were originally used for one of their early calculators. The Centronics parallel interface quickly became a de facto industry standard; manufacturers of the time tended to use various connectors on the system side, so a variety of cables were required. For example, early VAX systems used a DC-37 connector, NCR used the 36-pin micro ribbon connector, Texas Instruments used a 25-pin card edge connector and Data General used a 50-pin micro ribbon connector.

Dataproducts introduced a very different implementation of the parallel interface for their printers. It used a DC-37 connector on the host side and a 50 pin connector on the printer side—either a DD-50 (sometimes incorrectly referred to as a "DB50") or the block shaped M-50 connector; the M-50 was also referred to as Winchester. [cite web |url= |title=Dataproducts D-Sub 50 Parallel |accessdate=2008-01-25 |work=Hardware Book] [cite web |url= |title=Dataproducts M/50 Parallel |accessdate=2008-01-25 |work=Hardware Book] Dataproducts parallel was available in a short-line for connections up to convert|50|ft|m and a long-line version for connections from convert|50|ft|m to convert|500|ft|m. The Dataproducts interface was found on many mainframe systems up through the 1990s, and many printer manufacturers offered the Dataproducts interface as an option.

IBM released the IBM Personal Computer in 1981 and included a variant of the Centronics interface— only IBM logo printers (rebranded from Epson) could be used with the IBM PC. cite web|url= |title=Centronics and IBM Compatible Parallel Printer Interface Pin Assignment Reference |accessdate=2007-10-05 |last=Durda IV |first=Frank |date=2004 ] IBM standardized the parallel cable with a DB25F connector on the PC side and the Centronics connector on the printer side. Vendors soon released printers compatible with both standard Centronics and the IBM implementation.

IBM implemented an early form of bidirectional interface in 1987. HP introduced their version of bidirectional, known as "Bitronics", on the LaserJet 4 in 1992. The Bitronics and Centronics interfaces were superseded by the IEEE 1284 standard in 1994.


Before the advent of USB, the parallel interface was adapted to access a number of peripheral devices other than printers. Probably one of the earliest devices to use parallel were dongles used as a hardware key form of software copy protection. Zip drives and scanners were early implementations followed by external modems, sound cards, webcams, gamepads, joysticks and external hard disk drives and CD-ROM drives. Adapters were available to run SCSI devices via parallel. Other devices such as EPROM programmers and hardware controllers could be connected parallel.

Current use

At the consumer level, the USB interface—and in some cases Ethernet—has effectively replaced the parallel printer port. Many manufacturers of personal computers and laptops consider parallel to be a legacy port and no longer include the parallel interface. USB to parallel adapters are available to use parallel-only printers with USB-only systems. However, due to the simplicity of its implementation, it is often used for interfacing with custom-made peripherals, such as the RepRap 3d printer.

Implementation on IBM personal computers

Port addresses

Traditionally IBM PC systems have allocated their first three parallel ports according to the configuration in the table below.

Unidirectional parallel ports

In early parallel ports the data lines were unidirectional (data out only) so it was not easily possible to feed data in to the computer. However, a workaround was possible by using 4 of the 5 status lines. A circuit could be constructed to split each 8-bit byte into two 4-bit nibbles which were fed in sequentially through the status lines. Each pair of nibbles was then re-combined into an 8-bit byte.

ee also

* Parallel communications
* Parallel transmission
* IEEE 1284


* Axelson, Jan (2000). "Parallel Port Complete". [ Lakeview Research] . ISBN 0-9650819-1-5.
* [ The (Linux) Parallel Port Subsystem by Tim Waugh]

External links

* [ Interfacing to the Standard Parallel Port]
* [ Video on basics of standard parallel port]
* [ Parallel Port programming and interfacing]

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Look at other dictionaries:

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  • Parallel-Port — Parallel Port,   der Eingabe /Ausgabeanschluss für Geräte mit paralleler Schnittstelle. Er enthält 25 Pins, welche Kontrollsignale, Statussignale und Datensignale aufnehmen. Die Daten werden über acht Leitungen gleichzeitig (parallel) übertragen …   Universal-Lexikon

  • parallel port — noun count COMPUTING a connection between a computer and another piece of equipment, for example a printer, that uses more than one wire to carry information ─ compare SERIAL PORT …   Usage of the words and phrases in modern English

  • parallel port — UK / US noun [countable] Word forms parallel port : singular parallel port plural parallel ports computing a connection between a computer and another piece of equipment, for example a printer, that uses more than one wire to carry information •… …   English dictionary

  • parallel port — noun an interface between a computer and a printer where the computer sends multiple bits of information to the printer simultaneously • Syn: ↑parallel interface • Hypernyms: ↑interface, ↑port * * * ˈparallel port 7 [parallel port] …   Useful english dictionary

  • parallel port — lygiagretusis prievadas statusas T sritis informatika apibrėžtis ↑Prievadas, per kurį duomenys tarp kompiuterio ir išorinių jo įtaisų persiunčiami lygiagrečai, daugeliu laidų. Per lygiagretųjį prievadą dažniausiai jungiamas spausdintuvas.… …   Enciklopedinis kompiuterijos žodynas

  • parallel port — lygiagrečioji jungtis statusas T sritis informatika apibrėžtis ↑Jungtis, per kurią duomenys tarp kompiuterio ir išorinių jo įtaisų persiunčiami lygiagrečai, daugeliu laidų. Per lygiagrečiąją jungtį dažniausiai jungiamas spausdintuvas. atitikmenys …   Enciklopedinis kompiuterijos žodynas

  • parallel port —    An input/output (I/O) port that manages information eight bits at a time; often used to connect a parallel printer.    See also parallel communications; RS 232 C; serial communications; serial port …   Dictionary of networking

  • parallel port — /ˈpærəlɛl pɔt/ (say paruhlel pawt) noun Computers a port which enables several bits of data to be sent or received concurrently. Compare serial port …  

  • parallel port — noun A physical interface capable of transmitting multiple bits of data simultaneously, unlike a serial port …   Wiktionary

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