What Is The Parallel Port On Older PCs For?

Long before computers used USB slots and wireless communication to connect with accessories and peripherals, PCs relied on a diverse collection of ports. One of the most important connectors consisted of a 25-pin port called a parallel port, which was used to connect computers with printers.

The first parallel ports were designed between the 1970s and 1980s by IBM. The company wanted their then-upcoming PC to communicate with the top printer manufacturer of the time; Centronics. Centronics had its own connector, which used 36 pins, but IBM’s engineers decided to create a simpler port with 25 pins. How could they communicate? IBM’s engineers also designed a cable that bridged the gap between the two devices.

IBM’s parallel part was notable for several reasons. First off, it was a significant upgrade over the standard communication port of the time, the serial port. Whereas serial ports could only transmit bits of data in single file, the parallel port could send up to eight bits of data at a time in parallel to one another, hence its name. 

This technique significantly sped up data transference between computers and printers. Secondly, unlike, say, various types of USB-C adapters that convert signals, the parallel port and its cable didn’t need to do much if any conversions. The signals from each parallel port pin lined up with the first 25 pins in the Centronics printer.The parallel port was essentially a more streamlined version of Centronics’ design that cut out potentially superfluous pins.

While parallel ports are synonymous with printers — some people just call them printer ports because of this association — computer engineers found other uses. Waste not, want not, especially when it means sending and receiving data faster than other contemporary ports.

Quite obviously, parallel ports became the gold standard for printer communication, but as printer technology improved, their functions expanded well beyond the parallel port’s capabilities. Plus, some designers wanted to use parallel ports for new peripherals. 

Instead of inventing brand new port formats, computer designers simply improved what they already had. This design philosophy produced connectors such as the enhanced parallel port and the enhanced capabilities port, which preserved the original 25-pin shape, but increased communication speed and added features such as bi-directional communication. In many ways, the evolution of the different USB generations mirrors the evolution of the parallel port.

Of course, all good things must come to an end, and that included the parallel port’s relevance. Today, if you aren’t using Wi-Fi to send data to printers, you’re using USB cables, but why was the latter format invented in the first place? To deal with port bloat. Designers wanted to create a universal system that let a variety of peripherals connect to computers. Instead of needing a specific port, a gadget could just use a USB to communicate with a computer. No more specialized ports for mice and keyboards, and no more parallel ports for printers or external storage devices. Yes, the USB killed the parallel port, but given how USBs revolutionized the way we use computers, that’s a sacrifice we can support.