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 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.

Physical layout is the actual positioning of keys on a keyboard. Visual layout is the arrangement of the legends (labels, markings, engravings) that appear on those keys. Functional layout is the arrangement of the key-meaning association or keyboard mapping, determined in software, of all the keys of a keyboard; it is this (rather than the legends) that determines the actual response to a key press.

Modern computer keyboards are designed to send a scancode to the operating system (OS) 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 (default) visual layout to the OS when connected (though the user is still able to reset this at will).

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 Esc and Break—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.

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 Space bar on the bottom row. The positioning of the character keys is similar to the keyboard of a typewriter.

Besides the character keys, a keyboard incorporates special keys that do nothing by themselves but modify the functions of other keys. For example, the ⇧ Shift key can be used to alter the output of character keys, whereas the Ctrl (control), Alt (alternate) and AltGr (alternative graphic) keys trigger special operations when used in concert with other keys. (Apple keyboards have differently labelled but equivalent keys, see below).

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.