parallelport

The parallel port is a computer interface used to connect peripherals, most notably printers. It originated in the IBM PC era as a Centronics-based interface and became known as the LPT port. The host side typically uses a 25-pin D-sub connector, while the device side uses a Centronics-style connector or a similar arrangement. The interface transmits eight data lines in parallel and several control and status lines to coordinate data transfer, using simple handshaking signals such as strobe, acknowledge, and busy.

Standard Parallel Port (SPP) provided unidirectional data transfer from the host to the device. Later enhancements added bidirectional capability and higher speeds: Enhanced Parallel Port (EPP) and Extended Capabilities Port (ECP). These modes enable faster data transfer and, in some implementations, direct memory access. Practical data rates vary by mode and hardware, from tens of kilobytes per second in SPP to multiple megabytes per second in EPP/ECP.

In computer systems, a parallel port is typically addressed via dedicated I/O port space (for example, LPT1 at 0x378 on many PCs) rather than memory-mapped I/O. Operating systems provide device drivers to access the port, and software can bit-bang the lines or transfer blocks through the parallel port.

The parallel port was widely used from the 1980s through the 1990s for printers and other peripherals, but has largely been supplanted by USB and network interfaces. It remains in use in some industrial, laboratory, and legacy equipment, and is supported on modern systems via add-on cards or USB-to-parallel adapters. Developers and hobbyists also leverage parallel interfaces in microcontroller and hardware projects.