The power key, or power button, is a key found on many computer

keyboard Keyboard may refer to: Text input * Keyboard, part of a typewriter * Computer keyboard ** Keyboard layout, the software control of computer keyboards and their mapping ** Keyboard technology, computer keyboard hardware and firmware Music * Musi ...

s during the 1980s and into the early 2000s. They were introduced on the first Apple Desktop Bus keyboards in the 1980s and have been a standard feature of many

Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...

keyboards since then. They are also found on an increasing number of

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

keyboards, sometimes supplanted with additional keys for

sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...

. The power key is becoming increasingly rare, as most modern

personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...

s using

USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad v ...

allow the system to be started up by pressing any key on the keyboard.

Mac

The Apple Desktop Bus (ADB) was introduced on the Apple IIGS in 1986. This

peripheral bus In computing, a peripheral bus is a bus (computing), computer bus designed to support computer peripherals like printer (computing), printers and hard drives. The term is generally used to refer to systems that offer support for a wide variety of de ...

was intended to connect low-speed input devices like

s and

computer mice A computer mouse (plural mice, sometimes mouses) is a hand-held pointing device that detects two-dimensional space, two-dimensional motion relative to a surface. This motion is typically translated into the motion of a pointer (user interface ...

. Looking for a low-cost connector, the design team selected the 4-pin

mini-DIN The 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. Design Mini-DIN connectors are in diameter and come in seven patterns, wit ...

connector, which is also used for

S-Video S-Video (also known as separate video, Y/C, and erroneously Super-Video ) is an analog video signal format that carries standard-definition video, typically at 525 lines or 625 lines. It encodes video luma and chrominance on two separate channe ...

. ADB only used one data pin and +5V and ground, leaving one pin free. This was used to implement the ''PSW'' connection, used to turn on the machine. A separate connection was required as the keyboard controller of machines of this era was not powered when the machine was powered down. Introduced along with the IIGS was the Apple Keyboard, which featured a rather large power key roughly centered above the main part of the keyboard. A power key became a standard feature of all ADB keyboards, notably the lauded Apple Extended Keyboard and its follow-ons. It began to become less common on later USB-based keyboards as these machines keep the keyboard powered when the machine is sleeping, so any key can act as a power key. Power keys remain on some modern Macs, including the MacBook Air, but most others have replaced it with an "eject" key, formerly used to open the now-non-existent

CD drive In computing, an optical disc drive is a disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can only r ...

Windows

Early Windows PCs generally lacked the ability to control power through software, and power keys were not physically possible. The increasing use of USB connections allowed these, but the ability to use any key for "power on" generally negated their need in most cases. Power keys did become relatively common on some

multimedia keyboard The technology of computer keyboards includes many elements. Among the more important of these is the switch technology that they use. Computer alphanumeric keyboards typically have 80 to 110 durable switches, generally one for each key. The ch ...

s, where they were known as power management keys. Special keycodes are associated with these functions, e05e for Power, e05f for Sleep, and e063 Wake. These are supported in

and various

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

systems.

References

{{keyboard keys Computer keys