Modifier key
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In computing, a modifier key is a special key on a computer keyboard that modifies the normal action of another key when the two are pressed in combination.
For example, Alt+F4 in Microsoft Windows will close the program in the active window ; in this instance, Alt is the modifier key. In contrast, pressing just F4 will probably do nothing unless assigned a specific function in a particular program. By themselves, modifier keys usually do nothing, that is, pressing Alt alone does not trigger any action from the computer.
User interface expert Jef Raskin coined the term "quasimode" to describe the state a computer enters into when a modifier key is pressed.
Modifier keys on personal computers
The most common are:
- ⇧ Shift
- Ctrl
- Alt (Alternative)
- AltGr (Alternative Graphic)
- Super – called Windows key on Windows keyboards, Cmd key on Mac OS computers or Meta key on SUN.
- Fn (Function) – present on small-layout keyboard, usually on notebooks.
⇧ Shift is the oldest in terms of keyboards in general as it originates from typewriters and is usually used to make uppercase letters when typing.
Modifier keys in non-Windows platforms
In addition to the modifier keys on PCs, Apple Macintosh computers have the special Command key with the place of interest sign (⌘ Cmd) (and on older keyboards, the Open Apple symbol as well). Alt is replaced with the Option key (⌥ Opt); however Apple keyboards label this key with both "Option" and "Alt". When using a Windows keyboard, Macintoshes typically use the Windows key for the function of ⌘ Command. Ow! My key!
KDE and GNOME use the Windows key, called the Super key in these environments, as a modifier key. Some other X11 configurations assign to the Windows key the Hyper key symbol instead, but with the same purpose of acting as modifier.
Sun Microsystems keyboards have the Meta key (Inscription: ◆).
Amiga computers have two "Amiga keys" with an italicized 'A' as in the Amiga logo. The left key is used for commands to the application, like the Command key on Macintosh. The right key is used for commands to Workbench and the windowing system, much like the role of the Windows key on Windows. Both keys could be used together with other keys to emulate the mouse.
The Sinclair ZX Spectrum has a Symbol Shift key in addition to Caps Shift. This was used to access additional punctuation and keywords.
Compact keyboards, such as those used in laptops, often have a Fn key to save space by combining two functions that are normally on separate keys. On laptops, pressing Fn plus one of the function keys, e.g., F2, often control hardware functions.
The MIT space-cadet keyboard had additional Top, Front, Super and Hyper modifier keys. Combined with standard modifiers, it could enter as many as 8,000 different characters.
Accented characters
Some non-English language keyboards have special keys to produce accented modifications of the standard letter keys. In fact, the standard British keyboard layout includes an accent key on the top-left corner to produce àèìòù, although this is a two step procedure, press the accent key and release, then the letter key. These kinds of keys are called dead keys. The AltGr modifier produces the áéíóú sequence, or in conjunction with the Shift key, ÁÉÍÓÚ. Keyboards of some languages simply include the accented characters on their own keys. Some keyboards also have a Compose key for typing accented and other special characters. By pressing Compose, and then two other keys, something similar to a combination of the glyphs of the two previous keys will appear on the screen.
User interface difficulties
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In old, 1990s MS-DOS games, modifer keys such as Ctrl, Alt, Shift were often used extensively. For example, id Software's original DOOM series by default mapped the Ctrl key to fire a weapon, hold down Alt in conjunction with the arrow keys to strafe (move sideways), hold Shift and up or back arrow to run forwards and backwards. This kind of control scheme was copied by various game companies across multiple genres, including first-person shooter, fighting games, and others. With the introduction and standardization of the Windows key after Windows 95, this kind of control scheme became faulty because players could accidentally press the Windows key while trying to press Ctrl or Alt, and this in turn could interfere with DOS games run on top of Windows via the Dos prompt. The addition of the Windows Key to keyboards may have been part of the reason why most current games have evolved their control schemes, and most first person shooters generally use the mouse in conjunction with a "Half-Life" style of control (W,A,S,D, Space, Shift, Ctrl) named apparently because it may have been the first widespread game to popularize such an interface, and because usage of the Alt button would nowadays heighten the risk of accidentally pressing the Windows Key. To cope with this problem, some newer games (like Doom 3) disable the Windows Key while in the game.