The PS/2 connector is used for connecting some keyboards and mice to a PC compatible computer system. Its name comes from the IBM Personal System/2 series of personal computers, with which it was introduced in 1987. The PS/2 mouse connector generally replaced the older DE-9 RS-232 "serial mouse" connector, while the keyboard connector replaced the larger 5-pin DIN used in the IBM PC/AT design. The PS/2 keyboard and mouse interfaces are electrically similar and employ the same communication protocol. However, a given system's keyboard and mouse port may not be interchangeable since the two devices use a different set of commands. Following the release of USB keyboards, PS/2 keyboards and mice have become less popular.
The official technical specification for the PS/2 mouse and keyboard interfaces was found in the IBM PS/2 Hardware Interface Technical Reference Manual. However, by the late 1990's this manual was no longer being printed or sold and few products at that time strictly conformed to it. Most information currently found on this topic is based on a de facto set of standards (currently found here) originally published in 1998 by Adam Chapweske, a then-student at North Dakota State University. Chapweske's documentation is generally congruous with IBM's specification, but assumes a somewhat larger scope and redefines several parameters to reflect actual usage.
Original PS/2 connectors were black or had the same color as the connecting cable (mainly white). Later PC 97 color code was introduced. PC 97 made the keyboard port, and the plugs on compliant keyboards, purple; mouse ports and plugs were green. In the beginning, the color scheme was not consistent between vendors. Logitech used the color orange for the keyboard connector for a short period, but switched to purple soon. As of 2008, this code is still used on most PCs. The pins on the connectors are the same, but most devices are not electronically compatible. Care should be taken to avoid connecting a keyboard to a mouse port or vice versa."Cables Guide". Retrieved 2009-02-07