The
PS/2 connector is a 6-pin
Mini-DIN connectorThe mini-DIN connectors are a family of multi-pin electrical connectors used in a variety of applications. Mini-DIN is similar to the larger, older DIN connector...
used for connecting some
keyboardsIn computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...
and mice to a PC compatible computer system. Its name comes from the
IBM Personal System/2The Personal System/2 or PS/2 was IBM's third generation of personal computers. The PS/2 line, released to the public in 1987, was created by IBM in an attempt to recapture control of the PC market by introducing an advanced proprietary architecture...
series of
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s, with which it was introduced in 1987. The PS/2 mouse connector generally replaced the older DE-9
RS-232In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
"serial mouse" connector, while the PS/2 keyboard connector replaced the larger 5-pin/180°
DIN connectorA DIN connector is a connector that was originally standardized by the , the German national standards organization. There are DIN standards for a large number of different connectors, therefore the term "DIN connector" alone does not unambiguously identify any particular type of connector unless...
used in the IBM PC/AT design. The PS/2 designs on 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.
Port availability
Old
laptopA laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...
s generally have a single port that supports either a keyboard or a mouse. Sometimes the port also allows one of the devices to be connected to the two normally unused pins in the connector to allow both to be connected at once through a special splitter cable. This configuration is common on
IBMInternational Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
/Lenovo
ThinkpadThinkPad is line of laptop computers originally sold by IBM but now produced by Lenovo. They are known for their boxy black design, which was modeled after a traditional Japanese lunchbox...
notebooks among many others.
The PS/2 keyboard interface was electrically the same as the 5-pin AT system, and keyboards designed for one can be connected to the other with a simple wiring adapter. The PS/2 mouse interface is substantially different from RS-232 (which was generally used for mice on PCs without PS/2 ports), but nonetheless many mice were made that could operate on both with a simple wiring adapter.
PS/2 mouse and keyboard connectors have also been used in non-IBM PC-compatible computer systems, such as the DEC
AlphaStationAlphaStation was the name given to a series of computer workstations, produced from 1994 onwards by Digital Equipment Corporation, and latterly by Compaq and HP. As the name suggests, the AlphaStations were based on the DEC Alpha 64-bit microprocessor...
line, early IBM
RS/6000RISC System/6000, or RS/6000 for short, is a family of RISC and UNIX based servers, workstations and supercomputers made by IBM in the 1990s. The RS/6000 family replaced the IBM RT computer platform in February 1990 and was the first computer line to see the use of IBM's POWER and PowerPC based...
CHRPCHRP may refer to:*Common Hardware Reference Platform*Certified Human Resources Professional*Trigeneration...
machines and
SGISilicon Graphics, Inc. was a manufacturer of high-performance computing solutions, including computer hardware and software, founded in 1981 by Jim Clark...
IndyThe Indy, code-named "Guinness", is a low-end workstation introduced on 12 July 1993. Developed and manufactured by Silicon Graphics Incorporated , it was the result of their attempt to obtain a share of the low-end computer-aided design market, which was dominated at the time by other workstation...
, Indigo 2, and newer (
OctaneThe Octane and the similar Octane2 are UNIX workstations marketed by SGI. Both are 2-way SMP-capable workstations, originally based on the MIPS R10000 microprocessor. Newer Octanes are based on MIPS R12000 and R14000. The Octane2 has four improvements compared to Octane, a revised power supply,...
etc.) computers. Various Macintosh clone computers from the late 90s featured PS/2 mouse and keyboard ports, including the
Motorola StarMaxThe Motorola StarMax was a line of Macintosh clones produced by Motorola in 1996 and 1997. They used versions of Apple's Tanzania motherboard, which was designed to use standard IBM PC compatible components in addition to Apple-proprietary components then in common use in the Power Macintosh family...
and the Power Computing PowerBase
Legacy port status and USB
PS/2 was considered a
legacy portA legacy port is a computer port or connector that is considered fully or partially superseded. The replacement ports usually provide the functionality of the legacy ports with higher speeds, more compact design, or plug and play and hot swap for greater ease of use; special USB adapters are often...
by the
IntelIntel Corporation is an American multinational semiconductor chip maker corporation headquartered in Santa Clara, California, United States and the world's largest semiconductor chip maker, based on revenue. It is the inventor of the x86 series of microprocessors, the processors found in most...
/
MicrosoftMicrosoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
PC 2001 specification of 2000;
USBUSB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....
ports were preferred for connecting keyboards and mice. Despite this, PS/2 ports are included on most new motherboards. These PS/2 ports cause fewer problems when
KVM switchA KVM switch is a hardware device that allows a user to control multiple computers from a single keyboard, video monitor and mouse. Although multiple computers are connected to the KVM, typically a smaller number of computers can be controlled at any given time...
ing with non-
WintelWintel is a portmanteau of Windows and Intel, referring to personal computers using Intel x86 compatible processors running Microsoft Windows...
systems. PS/2 ports may also be favored for security reasons in a corporate environment. Use of PS/2 ports for keyboard and mouse connectivity would allow USB ports to be totally disabled, preventing the connection of any USB removable disks. Also, with high-end keyboards, the only way to provide
full n-key rolloverRollover is the ability of a computer keyboard to correctly handle several simultaneous keystrokes.-Normal typing:During normal typing on a conventional computer keyboard, only one key is typically being pressed by the user at any given time; each key is released before the next key is struck. ...
is by using PS/2, as USB has a cap of 6 keys plus modifiers at the same time.
Many keyboards and mice can connect via either USB or PS/2, selecting the appropriate protocol at power-on. Such devices are generally equipped with a USB connector, and ship with a simple wiring adapter to allow connection to a PS/2 port. Older PS/2-only peripherals can be connected to a USB port via an active adapter, which generally provides a pair of PS/2 ports at the cost of one USB port.
Color code =
Original PS/2 connectors were black or had the same color as the connecting cable (mainly white). Later the PC 97 standard introduced a color code: the keyboard port, and the plugs on compliant keyboards, were purple; mouse ports and plugs were green. Some vendors initially used a different color code:
LogitechLogitech International S.A. is a global provider of personal peripherals for computers and other digital platforms headquartered in Romanel-sur-Morges, Switzerland. The company develops and markets products like peripheral devices for PCs, including keyboards, mice, microphones, game controllers...
used the color orange for the keyboard connector for a short period, but soon switched to purple. Today this code is still used on most PCs. The pinouts of the connectors are the same, but most computers will not recognize devices connected to the wrong port.
| Color |
Description |
| |
Purple |
Keyboard |
| |
Green |
Mouse |
Wiring inside keyboard cable varies widely. Here are some more common color codes, but the reader is cautioned that the only reliable method of determining color assignment is to confirm by measuring continuity to the connector.
| Description |
Common |
Alternate |
Alternate |
Alternate |
Alternate |
Alternate |
Alternate |
| +CLK In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome to coordinate actions of circuits...
|
|
Green |
|
Blue |
|
White |
|
Yellow |
|
White |
|
Blue |
|
Yellow |
| Data |
|
White |
|
Yellow |
|
Green |
|
Red |
|
Green |
|
Yellow |
|
Gray |
| GND |
|
Yellow |
|
Black |
|
Orange |
|
Gray |
|
Black |
|
White |
|
Black |
| Vcc Almost all integrated circuits have at least two pins that connect to the power rails of the circuit in which they are installed. These are known as the IC's power supply pins...
|
|
Red |
|
Red |
|
Blue |
|
Brown |
|
Red |
|
Orange |
|
Red |
Software issues
As of 2010, version 8.0 of
MicrosoftMicrosoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
's keyboard and mice drivers no longer supports PS/2 (even with USB adapters) in its supported keyboards and supported mice.
Hotplugging
PS/2 ports are designed to connect the digital I/O lines of the microcontroller in the external device directly to the digital lines of the microcontroller on the motherboard. They are
not designed to be
hot swappableHot swapping and hot plugging are terms used to describe the functions of replacing computer system components without shutting down the system...
. Hot swapping PS/2 devices usually does not cause damage because more modern microcontrollers tend to have more robust I/O lines built into them which are harder to damage than those of older controllers; however, hot swapping can still potentially cause damage on older machines, or machines with less robust port implementations.
If they are hot swapped, the devices must be similar enough that the driver running on the host system recognizes, and can be used with the new device. Otherwise, the new device will not function properly. While this is seldom an issue with standard keyboard devices, the host system rarely recognizes the new device attached to the PS/2 mouse port. In practice most keyboards can be hot swapped but this should be avoided.
Durability
PS/2 connectors are not designed to be plugged in and out very often, which can easily lead to bent or broken pins. PS/2 connectors only insert in one direction and must be rotated correctly before attempting connection. Most but not all connectors include an arrow or flat section which is usually aligned to the right or top of the jack before being plugged in. The exact direction may vary on older or non-ATX computers and care should be taken to avoid damage or bent pins when connecting devices. This issue is slightly alleviated in modern times with the advent of the PS/2 to USB adapter. Users can just leave the PS/2 plugged into the USB at all times and not risk damaging the pins this way.
Fault isolation
As noted, in a standard implementation both PS/2 ports are usually controlled by a single microcontroller on the motherboard. This makes design and manufacturing extremely simple and cheap. However, a rare side effect of this design is that a malfunctioning device can cause the controller to become confused, resulting in "both" devices acting erratically. The resulting problems can be difficult to troubleshoot (e.g. a bad mouse can cause problems that appear to be the fault of the keyboard).
A way to isolate the problem is to use a USB keyboard or mouse to determine which of the devices is at fault. A USB to PS/2 adapter can also be used to connect either of the devices to a USB port but the result can be undetermined because PS/2 and USB ports can use different voltages. Quality USB to PS/2 adapters have an integrated circuit that compensates the PS/2 - USB port voltage differences. Due to this difference it is recommend to avoid cheap adapters or try using a USB Keyboard or Mouse when troubleshooting PS/2 related errors.
See also
- Bus mouse
A bus mouse is a variety of PC mouse which is attached to the computer using a specialized interface...
- DIN connector
A DIN connector is a connector that was originally standardized by the , the German national standards organization. There are DIN standards for a large number of different connectors, therefore the term "DIN connector" alone does not unambiguously identify any particular type of connector unless...
- Din or AT Keyboard
The AT keyboard was a keyboard with 84 keys introduced with the IBM PC/AT computer. It succeeded the 83-key PC/XT keyboard and therefore did not have many of the features seen on modern keyboards such as arrow keys and dual ctrl and alt keys. It was later replaced with the 101-key Enhanced keyboard...
- DE-9 connector
- Universal Serial Bus
USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....
External links