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- For a list of keyboard shortcuts, see Table of keyboard shortcuts
The Alt key (pronounced //) on a computer keyboard is used to change (alternate) the function of other pressed keys. Thus, the Alt key is a modifier key, used in a similar fashion to the Shift key. For example, simply pressing "A" will type the letter a, but if you hold down either Alt key while pressing A, the computer will perform an Alt+A function, which varies from program to program. The international standard ISO/IEC 9995-2 calls it Alternate key. The key is located either side of the Space bar, but in non-US PC keyboard layouts, rather than a second Alt key, there is an 'Alt Gr' key to the right of the space bar. Both placements are in accordance with ISO/IEC 9995-2.
The standardized keyboard symbol for the Alt key (which may be used when the usual Latin lettering “Alt” is not preferred for labelling the key) is given in ISO/IEC 9995-7 as symbol 25, and in ISO 7000 “Graphical symbols for use on equipment” as symbol ISO-7000-2105. This symbol is encoded in Unicode as U+2387 alternative key symbol (⎇).
The Alt key has come to replace the Meta key of the old MIT keyboards. In their original function, both Alt and Meta would set the high bit of the signal generated by the key to 1 (for example, A generates 01000001 while Alt+A generates 11000001). However, in modern software, due to the requirement of the high bit for internationalisation, Alt no longer works in such a way.
Since the 1990s Alt has been printed on the Option key on most Mac keyboards. Alt is used in non-Mac software, such as Unix and Windows programs, but in OS X it is always referred as Option key. Option key's behaviour in Mac OS X differs slightly from that of the Windows Alt key (it is used as a modifier rather than to access pull-down menus, for example).
Alt key combinations
The Alt key is well known as part of the Control-Alt-Delete key combination, which in some operating systems brings up a task manager. If you use Mac OS, Alt+Cmd+Esc is used almost the same way. The X Window System also uses Control-Alt-Backspace, which usually causes the X server to shut down or restart.
Other well-known combinations which the Alt key is part of include Alt-F4, to close a window, and Alt-Tab, to switch between windows. Additionally, in many traditional GUI environments, including Microsoft Windows, Alt is used to access pull-down menus.
Alt key for special characters
In Microsoft Windows, holding down the Alt key while typing in numbers (often referred to as Alt codes) on the numeric keypad allows the user to type special characters not normally available on the keyboard. For example, holding down Alt while typing 0225 (Alt+0225) on the numeric keypad will result in á, the character at 225 in the codepage. These extended keyboard characters are useful for persons using foreign languages, mathematics, currency symbols, business use, etc. Some computers work the same if the Num Lock key is on.
Mac OS X
On a Macintosh, the Alt key is called the Option key. It is not used to enter numeric character codes. Instead, keyboard letters and numbers are used. The diagram below shows the special characters a US Mac keyboard will produce when the Option key is pressed.
The highlighted orange keys show the accents available from the combination of the Alt key and the keyboard characters e ` i n u. The accent then can be applied to associated letters both lower and uppercase. The additional characters a Mac will produce are a combination of both the ⌥ Option key and the ⇧ Shift key pressed down together. With this combination pressed the keyboard will now produce a different set or an uppercase version of the previous set in some cases.