Control key
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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 (^).
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[edit] History
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.
[edit] 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:
| ^X | Traditional notation |
| C-x | Emacs notation |
| CTRL-X | Old Microsoft notation |
| Ctrl+X | New Microsoft notation |
[edit] Examples
Different application programs, user interfaces, and operating systems use the various control key combinations for different purposes.
| Key combination | Microsoft Windows/KDE | Emacs/Linux (command line and programs using readline) |
|---|---|---|
| Ctrl+A | Select all | Beginning of line |
| Ctrl+B | Bold | Backward one character |
| Ctrl+C | Copy (can also be used as an alternative to Ctrl+Break to terminate an application) | Compound command (emacs) or terminate application |
| Ctrl+D | Font Window (Word Processing) | Forward delete or end of input |
| Ctrl+E | Center Alignment (Word Processing) | End of line |
| Ctrl+F | Find (usually a small piece of text in a larger document) | Forward one character |
| Ctrl+G | Go To (Line number) | Bell |
| Ctrl+H | History | Brings up the history menu |
| Ctrl+I | Italic | Lisp indent (rarely used) |
| Ctrl+K | Insert Hyperlink (Word 2007) | Kill (cut) text between cursor and end of line |
| Ctrl+L | Create List | Vertically center current line in window/terminal |
| Ctrl+M | Decrease margin by 1/2 inch (Microsoft Word) | Execute command |
| Ctrl+N | New (window, document, etc.) | Next line |
| Ctrl+O | Open | Insert (open) new line |
| Ctrl+P | Previous line | |
| Ctrl+Q | Quit application | Literal insert or resume application |
| Ctrl+R | Refresh page | Reverse search |
| Ctrl+S | Save | Search forward |
| Ctrl+T | Open New Tab | ? |
| Ctrl+U | Underline | Uppercase word |
| Ctrl+V | Paste | Page down |
| Ctrl+W | Close window or tab | Cut (into kill ring) |
| Ctrl+X | Cut | compound command |
| Ctrl+Y | Redo (sometimes Ctrl+Shift+Z is used for this) | Yank (paste from kill ring) |
| Ctrl+Z | Undo | Suspend program |
| Ctrl+End | Bottom (end of document or window) | undefined or rarely used |
| Ctrl+Home | Top (start of document or window) | undefined or rarely used |
| Ctrl+Ins | Copy | undefined or rarely used |
| Ctrl+PgDn | Next tab | undefined or rarely used |
| Ctrl+PgUp | Previous tab | undefined or rarely used |
| Ctrl+Tab | Next window or tab | undefined or rarely used |
| Ctrl+Shift+Tab | Previous window or tab | undefined or rarely used |
| Ctrl+← | Previous word | undefined or rarely used |
| Ctrl+→ | Next word | undefined or rarely used |
| Ctrl+Alt+Backspace | ? | Restart X11 |
| Ctrl+Alt+Delete | Task Manager/ Restarting the Computer | Reboot (when on the console) |
[edit] 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; on a two-button mouse, you would 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.
[edit] See also
[edit] External links
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