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A parallel port is an interface used to connect peripheral hardware to a computer. It features two rows of small holes that accept rows of small pins on the cable. Parallel ports became popular due to their ability to transmit data in parallel at a faster rate than standard. The IEEE released standards to unify the technology, leading to the introduction of more peripherals. The USB and ethernet interfaces have replaced the parallel port, and most computer manufacturers no longer include it.
A parallel port is a type of interface found on computers that is used to connect various peripheral hardware to the computer. When a cable is plugged into the parallel port, the two devices are connected and able to communicate. A parallel port features two rows of small holes that accept rows of small pins on the cable, and there is usually a screw hole on each side of the port so that the cable can be securely attached to the computer. The port is often referred to as a printer port, and sometimes a Centronics port, after the Centronics 1970 Model 101 printer that included the first parallel interface for printers. Parallel ports are often identified within the computer 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 interface commonality, manufacturers did not use a universal connector, so a variety of parallel cables were required. During this period DC-37 connectors, 36-pin and 50-pin microribbon connectors, and 25-pin board edge connectors were produced to enable the use of the parallel interface.
Parallel ports became popular because they were capable of transmitting 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 plugged into a socket usually found on the back of the computer. Developers and manufacturers quickly adapted the technology to their products, leading to the introduction of many new printers and peripherals.
IBM released its own version of the personal computer, which included a parallel connector that shared many similarities with the Centronics connector. Hewlett Packard followed up with another version. While similar, there were differences in connection types which made peripheral development 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 somewhat unify the technology within the industry. These IEEE standards created a more unified set of connection types. The standard is known as “IEEE 1284” and establishes the parameters that define bi-directional parallel communication between devices and computers.
With the standardization of the connection came more printers, zip drives, scanners, external modems, webcams, gamepads and joysticks that used the parallel interface. Developers have produced adapters for running SCSI devices through parallel ports. Through the evolution of parallel communication, the Universal Serial Bus (USB) and ethernet interfaces were developed, effectively replacing the parallel port. Most computer manufacturers consider the parallel port to be the history of computing and no longer include a parallel interface.
