In computing, a Control key is a key, which when pressed in conjunction with another key, will perform a special operation. The Control key is a modifier key, it is used in the same fashion as the Shift key. Like the Shift Key, it is unusual for the control key to do anything when pressed by itself. The control key is located on or near the bottom left side of most keyboards. It is usually labeled Ctrl but sometimes Control or Ctl is seen.
On teletypewriters and early computer keyboards, holding down the Control key while pressing another key zeroed the leftmost 2 bits of the 7 bits in the generated ASCII character. This allowed the operator to produce the first 32 characters in the ASCII table. These are non-printing characters that signal the computer to control where the next character will be placed on the display device, eject a printed page or erase the screen, ring the terminal bell, or some other operation. Aptly, these characters are also called control characters.
Note that using the Control key with either lowercase c or uppercase C will generate the same ASCII code on a teletypewriter because holding down the control key grounds (zeros the voltage on) the 2 wires used to carry the leftmost 2 bits from the keyboard. In modern computers the interpretation of keypresses is generally left to the software, modern keyboards distinguish each physical key from every other and report all keypresses and releases to the controlling software. This additional flexibility is not often taken advantage of and it usually does not matter, for example, whether the control key is pressed in conjunction with an upper or a lower case character.
When the original purpose of the ASCII control characters became either obsolete or seldom used, later software appropriated the Control key combinations for other purposes.
There are several common notations for pressing the Control key in conjunction with another key. Each notation below means press and hold Control while pressing the c key:
|Ctrl-C||Old Microsoft notation|
|CTRL+C||New Microsoft notation|
Generally, the Command key, labeled with the ⌘ symbol on Apple Macintosh computers, performs the equivalent functions in Mac OS applications. (For example, Command+c copies, while Command+p prints; the same holds for saving, cutting, and pasting. Ironically, the use of these standardized keyboard commands across applications originated in the graphical Macintosh, before migrating to other platforms.) Apple Macintosh also has a Control key, but it performs other functions.
- It is mostly used as a modifier key for key-combinations.
- When pressing Control and clicking the mousebutton, you will get the Contextual menu. Same as when you press the Right mousebutton on a two-button mouse.
- It is used in commandline-mode for compatiblity with Unix-like programs.