Keyboard layout
A keyboard layout is any specific physical, visual, or functional arrangement of the keys, legends, or key-meaning associations of a computer keyboard, mobile phone, or other computer-controlled typographic keyboard. Standard keyboard layouts vary depending on their intended writing system, language, and use case, and some hobbyists and manufacturers create non-standard layouts to match their individual preferences, or for extended functionality.
is the actual positioning of keys on a keyboard. is the arrangement of the legends that appear on those keys. is the arrangement of the key-meaning association or keyboard mapping, determined in software, of all the keys of a keyboard; it is this that determines the actual response to a key press.
Modern computer keyboards are designed to send a scancode to the operating system when a key is pressed or released. This code reports only the key's row and column, not the specific character engraved on that key. The OS converts the scancode into a specific binary character code using a "scancode to character" conversion table, called the keyboard mapping table. This means that a physical keyboard may be dynamically mapped to any layout without switching hardware components—merely by changing the software that interprets the keystrokes. Often, a user can change keyboard mapping in system settings. In addition, software may be available to modify or extend keyboard functionality. Thus the symbol shown on the physical key-top need not be the same as appears on the screen or goes into a document being typed. Modern USB keyboards are plug-and-play; they communicate their visual layout to the OS when connected.
Key types
A computer keyboard consists of alphanumeric or character keys for typing, modifier keys for altering the functions of other keys, navigation keys for moving the text cursor on the screen, function keys and system command keys—such as and —for special actions, and often a numeric keypad to facilitate calculations.There is some variation between different keyboard models in the physical layout—i.e., how many keys there are and how they are positioned on the keyboard. However, differences between national layouts are mostly due to different selections and placements of symbols on the character keys.
Character keys
The core section of a keyboard consists of character keys, which can be used to type letters and other characters. Typically, there are three rows of keys for typing letters and punctuation, an upper row for typing digits and special symbols, and the on the bottom row. The positioning of the character keys is similar to the keyboard of a typewriter.Modifier keys
Besides the character keys, a keyboard incorporates special keys that do nothing by themselves but modify the functions of other keys. For example, the key can be used to alter the output of character keys, whereas the , and keys trigger special operations when used in concert with other keys..Typically, a modifier key is held down while another key is struck. To facilitate this, modifier keys usually come in pairs, one functionally identical key for each hand, so holding a modifier key with one hand leaves the other hand free to strike another key.
An alphanumeric key labelled with only a single letter can generally be struck to type either a lower case or capital letter, the latter requiring the simultaneous holding of the key. The key is also used to type the upper of two symbols engraved on a given key, the lower being typed without using the modifier key.
The Latin alphabet keyboard has a dedicated key for each of the letters A–Z, keys for punctuation and other symbols, usually a row of function keys, often a numeric keypad and some system control keys. In most languages except English, additional letters are required, and some are present as standard on each national keyboard, as appropriate for its national language. These keyboards have another modified key, labelled , to the right of the space bar.. It can be used to type an extra symbol in addition to the two otherwise available with an alphanumeric key, and using it simultaneously with the key usually gives access to a fourth symbol. These third-level and fourth-level symbols may be engraved on the right half of the key top, or they may be unmarked. Cyrillic alphabet and Greek alphabet keyboards have similar arrangements.
Instead of the, and keys seen on commodity keyboards, Apple Keyboards have and keys. The key is used much like the, and the key like the and, to access menu options and shortcuts. Macs have a key for compatibility with programs that expect a more traditional keyboard layout. It is especially useful when using a terminal, X11 or MS Windows. The key can generally be used to produce a secondary mouse click as well. There is also a key on modern Mac keyboards, which is used for switching between use of the,, etc. keys either as function keys or for other functions like media control, accessing Spotlight, controlling the volume, or handling Mission Control. key can also be found on smaller Windows and Linux laptops and tablets, where it serves a similar purpose.
Many Unix workstations keyboards placed the key to the left of the letter, and the key in the bottom left. This position of the key is also used on the XO laptop, which does not have a. The UNIX keyboard layout also differs in the placement of the key, which is to the left of.
Some early keyboards experimented with using large numbers of modifier keys. The most extreme example of such a keyboard, the so-called "space-cadet keyboard" found on MIT LISP machines, had no fewer than seven modifier keys: four control keys,,,, and, along with three shift keys,,, and. This allowed the user to type over 8000 possible characters by playing suitable "chords" with many modifier keys pressed simultaneously.
Dead keys
A dead key is a special kind of a modifier key that, instead of being held while another key is struck, is pressed and released before the other key. The dead key does not generate a character by itself, but it modifies the character generated by the key struck immediately after, typically making it possible to type a letter with a specific diacritic. For example, on some keyboard layouts, the grave accent key is a dead key: in this case, striking and then results in ; followed by results in . A grave accent in isolated form can be typed by striking and then.A key may function as a dead key by default, or sometimes a normal key can temporarily be altered to function as a dead key by simultaneously holding down the secondary-shift key— or : a typical example might be will produce . In some systems, there is no indication to the user that a dead key has been struck, so the key appears dead, but in some text-entry systems the diacritical mark is displayed along with an indication that the system is waiting for another keystroke: either the base character to be marked, an additional diacritical mark, or to produce the diacritical mark in isolation.
Compared with the secondary-shift modifier key, the dead-key approach may be a little more complicated, but it allows more additional letters. Using AltGr, only one or two additional letters with each key, whereas using a dead key, a specific diacritic can be attached to a range of different base letters.
Compose key
A Compose key can be characterized as a generic dead key that may, in some systems, be available instead of or in addition to the more specific dead keys. It allows access to a wide range of predefined extra characters by interpreting a whole sequence of keystrokes following it. For example, striking followed by and then results in á, followed by and then results in æ, and followed by and then results in ©.The key is supported by the X Window System. Some keyboards have a key labeled "Compose", but any key can be configured to serve this function. For example, the otherwise redundant right-hand key may, when available, be used for this purpose. This can be emulated in Windows with third-party programs, such as WinCompose.
System command keys
Depending on the application, some keyboard keys are not used to enter a printable character but instead are interpreted by the system as a formatting, mode shift, or special commands to the system. The following examples are found on personal computer keyboards.SysRq and PrtSc
The system request and print screen commands often share the same key. SysRq was used in earlier computers as a "panic" button to recover from crashes. The print screen command is used to capture the entire screen and send it to the printer, but in the present, it usually puts a screenshot in the clipboard.Break key
The Break key/Pause key no longer has a well-defined purpose. Its origins go back to teleprinter users, who wanted a key that would temporarily interrupt the communications line. The Break key can be used by software in several different ways, such as to switch between multiple login sessions, to terminate a program, or to interrupt a modem connection.In programming, especially old DOS-style BASIC, Pascal and C, Break is used to stop program execution. In addition to this, Linux and variants, as well as many DOS programs, treat this combination the same as Ctrl+C. On modern keyboards, the break key is usually labeled Pause/Break. In most Microsoft Windows environments, the key combination brings up the system properties.
Escape key
The escape key "nearly all of the time" signals Stop, QUIT, or "let me get out of a dialog".Another common application today of the key is to trigger the Stop button in many web browsers and operating systems.
ESC was part of the standard keyboard of the Teletype Model 33. The DEC VT50, introduced July 1974, also had an Esc key. The TECO text editor and its descendant Emacs use the Esc key extensively.
Historically, it also served as a type of shift key, such that one or more following characters were interpreted differently, hence the term escape sequence, which refers to a series of characters, usually preceded by the escape character.
On machines running Microsoft Windows, prior to the implementation of the Windows key on keyboards, the typical practice for invoking the "start" button was to hold down the control key and press escape. This process still works in Windows 10 and 11.