In computing, a modifier key is a special key on a computer keyboard that temporarily modifies the normal action of another key when pressed together. By themselves, modifier keys usually do nothing; that is, pressing any of the,, or keys alone does not trigger any action from the computer. For example, in most keyboard layouts the Shift key combination will produce a capital letter "A" instead of the default lower-case letter "a". A combination of in Microsoft Windows will close the active window; in this instance, Alt is the modifier key. In contrast, pressing just or will probably do nothing unless assigned a specific function in a particular program. User interface expert Jef Raskin coined the term "quasimode" to describe the state a computer enters into when a modifier key is pressed.
– Meta key, found on MIT, Symbolics, and Sun Microsystems keyboards
– found on Windows keyboards
– Command key, found on Apple Macintosh keyboards. On older keyboards marked with the Apple logo.
– present on small-layout keyboard, usually on notebooks.
The Meta key, Windows key, Cmd key, and the analogous "Amiga key" on Amiga computers, are usually handled equivalently. Under the GNU/Linux operating system, the desktop environmentKDE calls this key Meta, while GNOME calls this key, neutrally, Super. The Sinclair ZX Spectrum has a Symbol Shift key in addition to Caps Shift. This was used to access additional punctuation and keywords. The MSX computer keyboard, besides Shift and Control, also included two special modifier keys, Code and Graph. In some models, as in the Brazilian Gradiente Expert, the Code and Graph keys are labelled "" and "". They are used to select special graphic symbols and extended characters. Likewise, the Commodore 64 and other Commodore computers had the Commodore key at the bottom left of the keyboard. 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 plus one of the function keys, e.g., F2, often control hardware functions. Keyboards that lack a dedicated numeric keypad may mimic its functionality by combining the Fn key with other keys. 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 Latin-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, and then two other keys, something similar to a combination of the glyphs of the two previous keys will appear on the screen.
Dual-role keys
It is possible to use one same key both as a normal key and as a modifier. For example, you can use the both as a normal Space bar and as a Shift. Intuitively, it'll be a Space when you want a whitespace, and a Shift when you want it to act as a shift. I.e. when you simply press and release it, it is the usual space, but when you press other keys, say, and, while holding down the, then they will be treated as plus X, Y and Z. The above example is known as "SandS", standing for "Space and Shift" in Japan. But any number of any combinations are possible. To press shift+space in the previous example, you need in addition to a space/shift dual role key, one of another space/shift key, a usual shift, or a usual space key.
