A function key is a key on a computer or terminal keyboard which can be programmed so as to cause an operating system command interpreter or application program to perform certain actions. On some keyboards/computers, function keys may have default actions, accessible on power-on.

Function keys on a terminal may either generate short fixed sequences of characters, often beginning with the escape character (ASCII 27), or the characters they generate may be configured by sending special character sequences to the terminal. On a standard computer keyboard, the function keys may generate a fixed, single byte code, outside the normal ASCII range, which is translated into some other configurable sequence by the keyboard device driver or interpreted directly by the application program. Function keys may have (abbreviations of) default actions printed on/besides them, or they may have the more common "F-number" designations.

Function key schemes on various computer keyboards

• HP 9830 Circa 1972, f1-f8 on two rows of 4 in upper left with paper template label. Also on HP 2640 terminals. Earliest use of function keys on this list, if not in history.
• Screen labeled function keys Keys are placed in proximity or mapped to labels on CRT or LCD screen on calculator, computer, or kiosk screen. First introduced on HP 2640 series terminals in late 1970s
• Apple Macintosh: variously no function keys, or function keys F1 through F12, F1 through F15, or F1 through F16 across the top of the keyboard, depending on model
• Apple Macintosh laptops: F1 through F12, with pre-defined actions for F1 through F7 or F10, depending on model.

• Apricot PC/Xi: six unlabelled keys, each with a LED beside it which illuminates when the key can be used; above the keys is a liquid crystal display—the 'microscreen'—that is used by programs to display the action performed by the key
• BBC Micro: red/orange keys f0 to f9 in a horizontal row above the number keys on top of the computer/keyboard
• Atari 8-bit computers: Option, Select and Start keys; the XL models also had a Help key.
• Atari ST: ten fancy parallelogram-shaped keys in a horizontal row across the top of the keyboard, inset into the keyboard frame instead of popping up like normal keys
• Commodore Amiga: ten keys arranged in a row of two 5-key groups across the top of the keyboard (flush with the ordinary keyboard top row); function keys are 1.5× the width of ordinary keys
• Commodore VIC-20 and C64: F1/F2 to F7/F8 in a vertical row of four keys ascending downwards on the computer/keyboard's right hand side, odd-numbered functions accessed unshifted, even-numbered shifted; orange, beige/brown, or grey key color, depending on VIC/64 'submodel'
• Commodore 128: essentially same as VIC-20/C64, but with (grey) function keys placed in a horizontal row above the numeric keypad right of the main QWERTY-keyboard
• IBM 3270: early models, 12 function keys 3*4 at the right of keyboard, later 24 in two rows on top of the keyboard
• IBM PC AT and PS/2 keyboard: F1 to F12 usually in three 4-key groups across the top of the keyboard (the original IBM PC and PC XT keyboards had function keys F1 through F10, in two adjacent vertical rows on the left hand side; F1|F2, F3|F4, ..., F9|F10, ascending downwards)
• Sharp MZ-700: blue keys F1 to F5 in a horizontal row across the top left side of the keyboard, the keys are vertically half the size of ordinary keys and twice the width; there's also a dedicated 'slot' for changeable key legend overlays (paper/plastic) above the function key row
• MCK-142 Pro: 2 sets of F1-F12 function keys, 1 above QWERTY and one to the left. Also, 24 additional user programmable PF keys located above QWERTY keys.

Action of function keys on various programs, operating systems

In the Mac OS up to Mac OS 9, the function keys could be configured by the user, with the Function Keys control panel, to start a program or run an AppleScript. Mac OS X assigns default functionality to F9, F10, and F11 (Exposé); F12 (Dashboard); and F14/F15 (decrease/increase brightness). On newer Apple laptops, all the function keys are assigned basic actions such as volume control, brightness control, NumLock (since the laptops lack a keypad), and ejection of disks. Software functions can be used by holding down the Fn key while pressing the appropriate function key, and this scheme can be reversed by changing the Mac OS X system preferences.

Under MS-DOS, individual programs could decide what each function key meant to them, and the command line had its own actions (e.g., F3 copied to the current command prompt words from the previous command). The F1 key gradually became universally associated with Help in most early Windows programs. To this day, Microsoft Office programs running in Windows list F1 as the key for Help in the Help menu. Internet Explorer in Windows does not list this keystroke in the help menu, but still responds with a help window. F5 is also commonly used as a refresh key in many web browsers and other applications.

Other function key assignments common to all Microsoft Office applications are: F7 to check spelling, Alt-F8 to call the macros dialog, Alt-F11 to call the Visual Basic Editor and Shift-Alt-F11 to call the Script Editor. In Microsoft Word, Shift-F1 reveals formatting. In Microsoft PowerPoint, F5 starts the slide show, and F6 moves to the next pane.

WordPerfect for DOS is one of the programmes that made heavily use of function keys.

See also

• Common User Access

Computer keys

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