Guide to Ports and Plugs (Keyboard and Mouse Interfaces)

PS/2 ports were the previous standard before USB for keyboards and mice. They were no faster than Serial ports (see below) but were primarily created to help users by assigning a different shape to the port used for your keyboard (and mouse). This new plug was created by IBM when they launched their PS/2 line of computers in 1987, and while their concept of proprietary hardware failed to survive, many of their design ideas (including the color coded PS/2 ports for mice and keyboards) eventually became the industry standard. The technical term for the PS/2 keyboard interface is a Mini-DIN 6 plug (which replaced the previous standard which was the DIN 5 plug, known as the AT connector). The Mini-DIN 6 plug for the mouse replaced the 9 pin Serial port connector (see below).

Most computers manufactured prior to 2006 came with 2 PS/2 ports, a purple one for the keyboard and a green one for the mouse. Computers built more recently typically no longer have PS/2 ports on them, although some manufacturers are still supporting this standard, as there is no loss of performance in using a PS/2 interface for keyboards and mice. If you need more than one PS/2 port (i.e. for 2 PS/2 keyboards), you have to purchase a PS/2 splitter or a KVM switch.

A PS/2 plug (what is at the end of the cable which is attached to your keyboard (purple) or mouse (green)).
A PS/2 port (where you insert in your keyboard plug (purple) or mouse plug (green) into your computer).

Serial ports come in a wide range of sizes and shapes and were the original standard for interfacing any device with any other device on a computer. Today, they are rarely used and when one talks of a serial port, they usually mean the DB9 connector (shaped like a trapesoid). Typically they are only used on computers used in industrial environments or as a means of interfacing with an industrial control.