Caps Lock

Caps Lock is a button on a computer keyboard that causes all letters of bicameral scripts to be generated in capital letters. It is a toggle key: each press reverses the previous action. Some keyboards also implement a light to give visual feedback about whether it is on or off. Exactly what Caps Lock does depends on the keyboard hardware, the operating system, the device driver, and the keyboard layout. Usually, the effect is limited to letter keys. Letters of non-bicameral scripts (e.g. Arabic, Hebrew, Hindi) and non-letter characters are generated normally. The Caps Lock key originated as a Shift lock key on mechanical typewriters. An early innovation in typewriters was the introduction of a second character on each typebar, thereby doubling the number of characters that could be typed, using the same number of keys. The second character was positioned above the first on the face of each typebar, and the typewriter's Shift key caused the entire type apparatus to move, physically shifting the positioning of the typebars relative to the ink ribbon. Just as in modern computer keyboards, the shifted position was used to produce capitals and secondary characters. The Shift lock key was introduced so the shift operation could be maintained indefinitely without continuous effort. It mechanically locked the typebars in the shifted position, causing the upper character to be typed upon pressing any key. Because the two shift keys on a typewriter required more force to operate and were meant to be pressed by the little finger, it could be difficult to hold the shift down for more than two or three consecutive strokes, therefore the introduction of the Shift lock key was also meant to reduce finger muscle pain caused by repetitive typing. Mechanical typewriter shift lock is typically set by pushing both Shift and lock at the same time, and released by pressing Shift by itself. Computer Caps Lock is set and released by the same key, and the Caps Lock behavior in most QWERTY keyboard layouts differs from the Shift lock behavior in that it capitalizes letters but does not affect other keys, such as numbers or punctuation.