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In
computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, hardware and softw ...
, a Control key is a modifier key which, when pressed in conjunction with another key, performs a special operation (for example, ). Similarly to the
Shift key The Shift key is a modifier key on a alphanumeric keyboard, keyboard, used to type majuscule, capital letters and other alternate "upper" characters. There are typically two Shift keys, on the left and right sides of the row below the home row. T ...
, 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 (in accordance with the international standard ISO/IEC 9995-2), with many featuring an additional one at the bottom right. On keyboards that use English abbreviations for key labeling, it is usually labeled ( or are sometimes used, but it is uncommon). Abbreviations in the language of the keyboard layout also are in use, e.g., the German keyboard layout uses () as required by the German standard DIN 2137:2012-06. There is a standardized keyboard symbol (to be used when Latin lettering is not preferred). This symbol is encoded in
Unicode Unicode or ''The Unicode Standard'' or TUS is a character encoding standard maintained by the Unicode Consortium designed to support the use of text in all of the world's writing systems that can be digitized. Version 16.0 defines 154,998 Char ...
as U+2388 , but it is very rarely used.


History

On teletypewriters and
computer terminal A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. Most early computers only had a front panel to input or display ...
s, holding down the Control key while pressing another key would send an
ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...
C0 control character, instead of directly reporting a key press to the system. The control characters were used as non-printing characters that signal the terminal or teletypewriter to perform a special action, such as ringing a bell, ejecting a page or erasing the screen, or controlling where the next character will display. The first 32 ASCII characters are the control characters, representable by a 5- bit binary number. Because ASCII characters were represented as 7 bits, if a key is pressed while the Control key was held down, teletypewriters and terminals would simply set the first 2 bits of a character to 0, converting the character into a control character. For example, the character has a binary ASCII code of 110 0001. This code would be converted to 000 0001, corresponding to the ASCII character with id 1 (the SOH Character). The table at shows the ASCII control characters, with the "
Caret notation Caret notation is a notation for control characters in ASCII. The notation assigns to control-code 1, sequentially through the alphabet to assigned to control-code 26 (0x1A). For the control-codes outside of the range 1–26, the ...
" column showing a caret (^), followed by the character to press while the Control key is held down to generate the character. If a teletypewriter or terminal is connected to a computer, the software on the computer can interpret control characters it receives however it is written to do so; a given control character can be interpreted differently from how it would be interpreted by a teletypewriter or terminal that receives it. For example, Control-C, received from a teletypewriter or terminal, is interpreted as "interrupt the current program" in some
command-line interface A command-line interface (CLI) is a means of interacting with software via command (computing), commands each formatted as a line of text. Command-line interfaces emerged in the mid-1960s, on computer terminals, as an interactive and more user ...
s, and Control-E is interpreted by the
Emacs Emacs (), originally named EMACS (an acronym for "Editor Macros"), is a family of text editors that are characterized by their extensibility. The manual for the most widely used variant, GNU Emacs, describes it as "the extensible, customizable, s ...
text editor as "move the editor cursor to the end of the line".
Computer keyboard A computer keyboard is a built-in or peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or Push-button, keys to act as Mechanical keyboard, mechanical levers or Electronic switching system, electro ...
s directly attached to a computer, as is the case for a
personal computer A personal computer, commonly referred to as PC or computer, is a computer designed for individual use. It is typically used for tasks such as Word processor, word processing, web browser, internet browsing, email, multimedia playback, and PC ...
or
workstation A workstation is a special computer designed for technical or computational science, scientific applications. Intended primarily to be used by a single user, they are commonly connected to a local area network and run multi-user operating syste ...
, distinguish each physical key from every other and report all keypresses and releases to the controlling software. This allows the software to interpret Control key combinations as it chooses, including being able to interpret a combination of the Control key, another modifier key, and a letter, number, or symbol key differently from the way it interprets a combination of the Control key and the letter, number, or symbol key without that other modifier key.


Location

The keyboards of many early
computer terminal A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. Most early computers only had a front panel to input or display ...
s, including the Teletype Model 33 ASR and Lear-Siegler ADM-3A, and early models of the
IBM PC The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the List of IBM Personal Computer models, IBM PC model line and the basis for the IBM PC compatible ''de facto'' standard. Released on ...
, positioned the Control key on the left of the keyboard, whereas caps lock resides in the same position on most modern keyboards. The traditional layout was preserved for later
workstation A workstation is a special computer designed for technical or computational science, scientific applications. Intended primarily to be used by a single user, they are commonly connected to a local area network and run multi-user operating syste ...
systems and is often associated with
Unix Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...
workstations. Keyboards from
Sun Microsystems Sun Microsystems, Inc., often known as Sun for short, was an American technology company that existed from 1982 to 2010 which developed and sold computers, computer components, software, and information technology services. Sun contributed sig ...
came in two layouts; "Unix" and "PC-style", with the Unix layout having the traditional placing of the Control key and other keys. The keyboards produced for One Laptop Per Child computers also have the Control key in this location. Other vendors produce keyboards for different computer systems with this placement of the Control key, such as the Happy Hacking Keyboard. Some users of keyboards with caps lock on the left 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. Keyboard layout preferences specifically to address this need are available in some operating systems. 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 while pressing the key:


Table of examples

Different application programs, user interfaces, and operating systems use the various control key combinations for different purposes. In early
first-person shooter A first-person shooter (FPS) is a video game genre, video game centered on gun fighting and other weapon-based combat seen from a First person (video games), first-person perspective, with the player experiencing the action directly through t ...
s, the left Ctrl key is often used to fire a weapon. In newer games, the key is often used for crouching instead.


Similar concepts

Generally, the Command key, labeled with the ⌘ symbol on Apple Macintosh computers, performs the equivalent functions in
classic Mac OS Mac OS (originally System Software; retronym: Classic Mac OS) is the series of operating systems developed for the Mac (computer), Macintosh family of personal computers by Apple Computer, Inc. from 1984 to 2001, starting with System 1 and end ...
and
macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...
applications (for example, copies, while prints; the same holds for saving, cutting, and pasting).
Macintosh Mac is a brand of personal computers designed and marketed by Apple Inc., Apple since 1984. The name is short for Macintosh (its official name until 1999), a reference to the McIntosh (apple), McIntosh apple. The current product lineup inclu ...
es 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 Classic Mac OS and macOS, the Control key is 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. * Pressing Control and clicking the mouse button will invoke 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
macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...
, the Control key allows the use of
Emacs Emacs (), originally named EMACS (an acronym for "Editor Macros"), is a family of text editors that are characterized by their extensibility. The manual for the most widely used variant, GNU Emacs, describes it as "the extensible, customizable, s ...
-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.


Notes


References


See also

* Alt key * Break key *
Control characters In computing and telecommunications, a control character or non-printing character (NPC) is a code point in a character set that does not represent a written character or symbol. They are used as in-band signaling to cause effects other than ...
* Control-Alt-Delete *
Function key A function key is a key on a computer or computer terminal, terminal computer keyboard, keyboard that can be programmed to cause the operating system or an application program to perform certain actions, a form of soft key. On some keyboards/com ...
*
Keyboard layout A keyboard layout is any specific physical, visual, or functional arrangement of the keys, legends, or key-meaning associations (respectively) of a computer keyboard, mobile phone, or other computer-controlled typographic keyboard. Standard keybo ...
* Modifier key * IBM Common User Access {{DEFAULTSORT:Control Key Computer keys