control key

It has been suggested that Control key (Macintosh) be merged into this article or section. (Discuss)

A Control key (marked "Ctrl") on a modern Windows keyboard

In computing, a Control key is a modifier key which, when pressed in conjunction with another key, will perform a special operation (for example, Control-Alt-Delete); similar to the Shift key, the Control key rarely performs any function 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, and it can be graphically represented as an “up arrowhead” (U+2303, ⌃), or simulated with a caret (^).

History

Control key on an Apple wireless keyboard

On teletypewriters and early 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.

Because on older keyboards the Control key was located on the left of the keyboard, some people remap the keys to exchange Control and Caps Lock, finding the traditional location more ergonomic for using programs benefiting from use of the Control key. This is sometimes called "Unix" layout; Sun5 model keyboards from Sun Microsystems came in two versions; Sun5pc and Sun5unix, with the latter having more traditional placing of some keys, including the Control key. The OLPC XO-1 keyboard also has the Control key in this location. Keyboards for different computer systems with this placement of the Control key are also sold as extra peripherals, see for example the Happy Hacking Keyboard.

Others leave the control key in the lower-left corner of the keyboard, and press it using the side of their palm. The choice of location for the control key often comes down to the typist's hand shape and posture.

Notation

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 x key:

OS X uses the Traditional notation.

Examples

Different application programs, user interfaces, and operating systems use the various control key combinations for different purposes.

Similar concepts

Generally, the Command key, labeled with the ⌘ symbol on Apple Macintosh computers, performs the equivalent functions in Mac OS X and Mac OS applications (for example, ⌘C copies, while ⌘P prints; the same holds for saving, cutting, and pasting).

Macintoshes also have a Control key, but it has different functionality.

• It is mostly used as a modifier key for key-combinations.
• When pressing Control and clicking the mouse-button, you will get a contextual menu. This is a compatibility feature for users with one-button mice; users with two-button mice just use the right mouse-button, with no modifiers.
• It is used in the command line interface with programs made for that interface.
• Under Mac OS X, the Control key allows the use of Emacs-style key combinations in most text entry fields. For example, Ctrl-A moves the caret to the start of the paragraph, Ctrl-L vertically centers the current line in the editing field, Ctrl-K cuts text to the end of the line to a kill ring separate from the normal clipboard, etc.

See also

• Alt key
• Break key
• Control characters
• Control-Alt-Delete
• Function key
• Keyboard layout
• Modifier key

IBM/Windows keyboard (US layout) v • d • e
Esc		F1	F2	F3	F4		F5	F6	F7	F8		F9	F10	F11	F12		PrtSc/ SysRq	ScrLk	Pause/ Break
																	Ins	Home	PgUp		NumLk	/	*	-
																	Del	End	PgDn		7	8	9	+
																					4	5	6
																		↑			1	2	3	Ent
																	←	↓	→		0		.