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, with many featuring an additional one at the bottom right. 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 (^).
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.
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 a "Unix" layout. Keyboards from Sun Microsystems came in two layouts; Unix and PC-style, with the Unix layout having the traditional placing of the Control key and other keys. 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. After the Mac OS became a Unix based OS, a keyboard-preference setting was added specifically to address this need.
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.
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 Ctrl/X OpenVMS notation
Different application programs, user interfaces, and operating systems use the various control key combinations for different purposes.
Key combination Microsoft Windows/KDE/GNOME Unix (command line and programs using readline) Emacs (if different from Unix command line) 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) terminate application Compound command Ctrl+D Font Window (Word Processing); Add to bookmarks (Browsers) Forward delete, or if line is empty, end of input (traditional Unix) Forward delete 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 Quit - aborts current operation Ctrl+H Replace, or History in browsers Delete previous character Help key Ctrl+I Italic (sometimes incremental search) Command line completion Same as Tab key Ctrl+J Justify Line feed (LFD) LFD (to evaluate Lisp expressions) Ctrl+K Insert Hyperlink (Word 2007) Cut ("Kill") text between cursor and end of line Ctrl+L Create List, Left align (word processing) Clear screen Redraw window/terminal, and recenter view around current line Ctrl+M Decrease margin by 1/2 inch (Microsoft Word) Same as Enter key Ctrl+N New (window, document, etc.) Next line (in history) Next line Ctrl+O Open Flush output Insert ("open") new line Ctrl+P Previous line (in history) Previous line Ctrl+Q Quit application Resume transmission Literal insert Ctrl+R Refresh page, Right align (word processing) Search backwards in history Search backwards Ctrl+S Save Pause transmission Search forward Ctrl+T Open New Tab Transpose characters Ctrl+U Underline Delete text between beginning of line and cursor Prefix numerical argument to next command Ctrl+V Paste Literal insert Page down Ctrl+W Close window or tab Delete previous word Cut Ctrl+X Cut Compound command Ctrl+Y Redo (sometimes Ctrl+Shift+Z is used for this) Paste Ctrl+Z Undo Suspend program Iconify window Ctrl+[ Decrease font size Same as Esc key Same as Modifier key (Alt key) Ctrl+End Bottom (end of document or window) undefined or rarely used Bottom (end of text buffer) Ctrl+Home Top (start of document or window) undefined or rarely used Top (start of text buffer) Ctrl+Ins Copy undefined or rarely used Copy Ctrl+PgDn Next tab undefined or rarely used Scroll window to the right Ctrl+PgUp Previous tab undefined or rarely used Scroll window to the left 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 Previous word Ctrl + → Next word undefined or rarely used Next word Ctrl+Delete Delete Next word undefined or rarely used Delete Next word Ctrl+Backspace Delete Previous word undefined or rarely used Delete Previous word Ctrl+Alt+Backspace undefined or rarely used Restart X11 undefined or rarely used Ctrl + Alt + ↑ Rotate Screen Upside down unknown unknown Ctrl + Alt + ↓ Rotate Screen Right side up unknown unknown Ctrl + Alt + ← Rotate Screen left unknown unknown Ctrl + Alt + → Rotate Screen right unknown unknown Ctrl+Shift+Esc Task Manager unknown unknown Ctrl+Alt+Delete Windows Security/Task Manager Reboot (when on the console) undefined or rarely used
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. The original Apple mouse design reduced complexity by only offering one button. As the interface developed, Contextual Menus were offered to access extra options. Another button was needed to access these. On Unix and Windows, the user had other mouse buttons to use. On Mac OS, the Control key was used to invoke a "right-click". Apple calls this a "secondary click" as left-handers can choose which side this button is on.
- 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.
- In Quickbooks, the Control Key is used to validate login credentials during OLSU 1016 and OLSU 1013 errors. Keeping it depressed while sending information to the Quickbooks servers fixes the errors.
- 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.
Esc F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 PrtScn/
Ins Home PgUp Num Lock / * - Del End PgDn 7 8 9 + 4 5 6 ↑ 1 2 3 Ent ← ↓ → 0 . Keyboard keys Dead keys Modifier keys Lock keys Navigation Editing Misc.
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