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 Apple Desktop Bus (ADB) is a proprietary bit-serial peripheral bus connecting low-speed devices to computers. It was introduced on the Apple IIGS in 1986 as a way to support low-cost devices like keyboards and mice, allowing them to be connecte ...

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. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and software en ...

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

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

Mac

The

(ADB) was introduced on the

Apple IIGS The Apple IIGS (styled as II), the fifth and most powerful of the Apple II family, is a 16-bit personal computer produced by Apple Computer. While featuring the Macintosh look and feel, and resolution and color similar to the Amiga and Atari ST ...

in 1986. This peripheral bus 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 chan ...

. 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 The Apple Extended Keyboard (AEK, model M0115) is a keyboard that was first sold separately alongside the Macintosh II and SE starting in 1987. It was replaced in 1990 by the Apple Extended Keyboard II (AEKII, model M3501) which was pre-packag ...

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 The MacBook Air is a line of ultrabook computers developed and manufactured by Apple Inc. It consists of a full-size keyboard, a machined aluminum case, and, in the more modern versions, a thin light structure. The Air was originally position ...

, 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 ...

Windows

Early

Windows PC 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 ser ...

s 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 keyboards, 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 Microsoft Windows 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