Parallel port

Parallel computer printer port

25 Pin D-sub pinout

Centronics-36F

Mini-Centronics 36 pin with Micro-Centronics 36 pin

Apple II Parallel Printer Card

HP C4381A CD-Writer Plus 7200 Series-4077

Parallel port is a type of interface found on computers for connecting peripherals. The parallel port became a standard printer port for personal computers in the 1980s and 1990s. It was originally developed by Centronics, a company in the computer printers industry, which is why it is also known as the Centronics port. The parallel port is known for its ability to transfer multiple bits of data simultaneously, as opposed to serial ports which send data bit by bit. This capability made parallel ports faster than serial ports for data transfer, but they have been largely replaced by more advanced interfaces such as USB and Ethernet in modern computing.

History

The parallel port was introduced in the 1970s. The design was significantly improved by IBM with the introduction of the IBM PC in 1981, which set the standard for parallel port implementations, making it a ubiquitous interface for connecting printers and other peripherals to computers. The IEEE 1284 standard, released in 1994, further defined the operation of parallel ports, ensuring compatibility and enhancing functionality across different devices.

Technical Details

A standard parallel port operates by sending 8 bits of data at a time over 8 separate wires, with additional wires used for control signals. This allows for a byte (8 bits) of data to be transmitted simultaneously, facilitating relatively fast data transfer rates. The IEEE 1284 standard introduced several modes of operation, including:

- Compatibility Mode: The original, unidirectional data transfer method, primarily used for connecting printers. - Nibble Mode: A bidirectional mode that allows for data transfer in both directions, but only 4 bits at a time. - Byte Mode: A bidirectional mode that transfers data 8 bits at a time. - ECP (Enhanced Capability Port) Mode: Offers high-speed, bidirectional data transfer and is capable of DMA (Direct Memory Access) for even faster data processing. - EPP (Enhanced Parallel Port) Mode: Also allows for high-speed, bidirectional data transfer, but is designed to be easier to implement in software.

Usage

While the parallel port was primarily used to connect printers, it was also utilized for connecting other devices such as scanners, external hard drives, and network adapters. In addition, the parallel port was popular in the hobbyist community for DIY projects and robotics due to its straightforward, direct access to hardware.

Decline

The advent of USB in the mid-1990s began the decline of the parallel port, as USB offered several advantages over parallel connections. USB ports are more flexible, can connect a larger number of devices, offer higher data transfer rates, and provide power to connected devices. As a result, manufacturers gradually phased out parallel ports from computers and peripherals. Today, parallel ports are rarely found on new computers, though they are still used in some industrial and legacy systems.

Legacy

Despite its decline in use, the parallel port played a crucial role in the development of computer peripherals and the expansion of personal computing. Its design and functionality laid the groundwork for the development of modern high-speed data transfer interfaces.

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