A parallel port is a kind of interface found on computers that is used to connect different peripheral hardware to the computer. When a cord is attached to the parallel port, the two devices are connected and are able to communicate. A parallel port is characterized by two rows of small holes that accept the rows of small pins on the cord, and there usually is a screw hole on each side of the port so that the cord can be securely fastened to the computer. The port is often referred to as a printer port and sometimes as a Centronics port, from the 1970 Centronics Model 101 printer that included the first parallel interface for printers. Parallel ports often are identified within the computer's system as "LPT1" and "LPT2."
Developers Robert Howard and Prentice Robinson with Centronics introduced this interface, and it quickly became the industry standard. Despite the commonality of the interface, manufacturers did not use a universal connector, so a variety of parallel cables were required. DC-37 connectors, 36-pin and 50-pin micro ribbon connectors and 25-pin card edge connectors were produced during this time to enable use of the parallel interface.
Parallel ports became popular because they were able to transmit data in parallel at a faster rate than was standard at the time. Data sent over a parallel connection moved eight bits at a time, often through eight pin connectors. These connectors were plugged into a socket generally found on the back of the computer. Developers and manufacturers quickly adapted the technology to their own products, leading to the introduction of many new printers and peripherals.
IBM released its version of the personal computer, which included a parallel connector that shared many similarities with the Centronics connector. Hewlett Packard followed with another version. Although similar, there were differences in the connection types that made development of peripherals difficult because there was no standard for this type of connector.
In 1994, this was resolved when the Institute of Electrical and Electronics Engineers (IEEE) released a set of standards to unify the technology within the industry somewhat. These IEEE standards created a more unified set of connection types. The standard is known as "IEEE 1284" and sets forth the parameters that define bi-directional parallel communication between peripherals and computers.
With the standardization of connection came more printers, zip drives, scanners, external modems, webcams, gamepads and joysticks that made use of parallel interface. Developers manufactured adapters to run SCSI devices by parallel ports. Through the evolution of parallel communication, the Universal Serial Bus (USB) and ethernet interfaces were developed, and they have effectively replaced the parallel port. Most computer manufacturers consider the parallel port computer science history and no longer include a parallel interface.