What is a PS/2 Connector?

John Lister

A PS/2 connector is a plug and socket system used for connecting keyboards and mice to PC computers. It has largely been superseded by Universal Serial Bus (USB) connectors, but is still used on some machines. Relatively cheap adaptors can allow an input device with a PS/2 connector to work on a computer that only has USB sockets.

The PS/2 line established some standard formats that have since become outdated, such as a floppy disk drive.
The PS/2 line established some standard formats that have since become outdated, such as a floppy disk drive.

The PS/2 connector system consists of a plug with six circular pins and one flat pin, arranged roughly in a circle. Although the physical design of the connector and socket is the same for both keyboards and mice, the commands sent to the computer mean sockets and plugs for each are not necessarily interchangeable. To avoid conflicts, both sockets and plugs are color-coded: green for mice and purple for keyboards. This color system was introduced several years after the connectors debuted, as a response to customer confusion. It was part of the same color coding system by which analog monitors are connected with a blue plug and socket.

There are several inherent problems with the PS/2 connector system. One is that, on older machines at least, users who hotswapped devices — unplugged one device and replaced it with another — can cause confusion in the computer. The design of the device also meant it is relatively easy to damage the connector by unintentionally bending a pin. Another problem is that the sockets are relatively large, meaning that as computers became more portable and thus smaller, there was often not enough room to have one or even two PS/2 sockets.

USB connectors became the preferred connection system for keyboards and mice for several reasons. The main reason was simply convenience: using USB means there is no need to specifically fit a keyboard and mouse slot on every machine. Another benefit is that USB arguably does a better job of carrying power to input devices, which is important with features such as optical mice that require a light-emitting diode.

The PS/2 connector gets its name from the IBM PS/2 line of computers, released in 1987. This line was a failed attempt by IBM to remain dominant control of the PC market: its failure led to the current system in which there are dozens, if not hundreds, of different PC manufacturers. Despite this failure, IBM's market position at the time was strong enough that the PS/2 connector became the then-standard way of connecting input devices to PCs. The PS/2 line also established some other standard formats that have since become outdated, most notably the 3.5 inch (about 89 millimeter) floppy disk drive.

The PS/2 connector should not be confused with Sony's Playstation 2 console, known commonly as the PS/2. This console does have a range of connectors specific to the console. These include the controllers used for playing game, the slots for external memory cards, and a special audiovisual socket that can connect to television sets through a range of connection leads via adaptors.

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