Jump to navigation Jump to search “LPT” redirects here. This article is about the Centronics style port. For the concept in general, see Parallel communications. A DB-25 connector often used for a parallel printer port on IBM Patch port interrupt in linux compatible computers, with the printer icon.
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. The parallel port interface was originally known as the Parallel Printer Adapter on IBM PC-compatible computers. An Wang, Robert Howard and Prentice Robinson began development of a low-cost printer at Centronics, a subsidiary of Wang Laboratories that produced specialty computer terminals. This left the problem of sending the ASCII data to the printer. While a serial port does so with the minimum of pins and wires, it requires the device to buffer up the data as it arrives bit by bit and turn it back into multi-bit values. ASCII value is presented on the pins in complete form.
The Centronics Model 101 printer, featuring this connector, was released in 1970. When the data was ready, the host pulled the STROBE pin low, to 0 V. The printer side of the interface quickly became an industry de facto standard, but manufacturers used various connectors on the system side, so a variety of cables were required. In theory, the Centronics port could transfer data as rapidly as 75,000 characters per second. This was far faster than the printer, which averaged about 160 characters per second, meaning the port spent much of its time idle.