page_title: IBM Personal System/2
section_title: Interface
hierarchical_section_title: IBM Personal System/2 / Technology / Keyboard/mouse / Interface
caption_attribution_description: English: PS/2 keyboard and mouse ports.
context_page_description: The Personal System/2 or PS/2 is IBM's third generation of personal computers. Released in 1987, it officially replaced the IBM PC, XT, AT, and PC Convertible in IBM's lineup. Many of the PS/2's innovations, such as the 16550 UART, 1440 KB 3.5-inch floppy disk format, Model M keyboard layout, 72-pin SIMMs, the PS/2 keyboard and mouse ports, and the VGA video standard, went on to become standards in the broader PC market.
  The PS/2 line was created by IBM partly in an attempt to recapture control of the PC market by introducing the advanced yet proprietary Micro Channel architecture on higher-end models. These models were in the strange position of being incompatible with the IBM-compatible hardware standards previously established by IBM and adopted in the PC industry. However IBM's initial PS/2 computers were popular with target market corporate buyers, and by 30th September 1988 IBM reported that it had sold 3 million PS/2 machines. This was only 18 months after the new range had been introduced.
  Most major PC manufacturers balked at IBM's licensing terms for MCA-compatible hardware, particularly the per-machine royalties.
context_section_description: PS/2 systems introduced a new specification for the keyboard and mouse interfaces, which are still in use today (though increasingly supplanted by USB devices) and are thus called "PS/2" interfaces. The PS/2 keyboard interface, inspired by Apple's ADB interface, was electronically identical to the long-established AT interface, but the cable connector was changed from the 5-pin DIN connector to the smaller 6-pin mini-DIN interface. The same connector and a similar synchronous serial interface was used for the PS/2 mouse port.
  The initial desktop Model 50 and Model 70 also featured a new cableless internal design, based on use of interposer circuit boards to link the internal drives to the planar (motherboard). Additionally these machines could be largely disassembled and reassembled for service without tools.
  Additionally, the PS/2 introduced a new software data area known as the Extended BIOS Data Area (EBDA). Its primary use was to add a new buffer area for the dedicated mouse port. This also required making a change to the "traditional" BIOS Data Area (BDA) which was then required to point to the base address of the EBDA.
  Another new PS/2 innovation was the introduction of bidirectional parallel ports which in addition to their traditional use for connecting a printer could now function as a high speed data transfer interface. This allowed the use of new hardware such as parallel port scanners, CD-ROM drives, and also enhanced the capabilities of printers by allowing them to communicate with the host PC and send back signals instead of simply being a passive output device.
caption: PS/2 connection ports (later colored purple for keyboard and green for mouse, according to PC 97) were once commonly used for connecting input devices.
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