The International Caps Lock Day Is Today

Caps lock is a key on many computer keyboards. Pressing it sets an input mode in which typed letters are uppercase by default (i.e. in All caps). The keyboard remains in caps lock mode until the key is pressed again. On some computers, holding down the shift key while caps lock is on temporarily switches to lowercase.
Keyboards often include a small LED to indicate that caps lock is active—either on the key itself, or in a row with scroll lock and num lock indicators. However, some new laptop and wireless desktop keyboards lack the LED, instead providing software that gives an on-screen indicator.

People typing case-sensitive passwords that are not displayed verbatim on the screen may not realize that caps lock is on, causing errors. Help guides, tech support materials, and sometimes the interface itself may include advice on checking caps lock before typing a password. In Windows login screens, a warning that caps lock is on is shown in a balloon near the field. In Mac OS X, when caps lock is on, a caps lock symbol (⇪) is displayed inside a password field. Operating systems may also provide audible notifications when caps-lock, num-lock, or scroll-lock buttons are toggled.

Some manufacturers include an option in the controller software to deactivate the caps lock key. This behaviour allows users to decide themselves whether they want to use the key, or to disable it to prevent accidental activation.

The caps lock key is a modified version of the shift lock key that occupies the same position on the keyboards of mechanical typewriters. An early innovation in mechanical 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 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.

Because the shift key mechanism on a mechanical typewriter requires more force to operate and is usually operated by the little finger on the left hand, it was difficult to hold the shift down for more than two or three consecutive strokes. The shift lock key was introduced so the shift operation could be maintained indefinitely without continuous effort. It literally locked the shift mechanism, causing the upper character to be typed upon pressing any key.

The caps lock key on modern QWERTY keyboards differs from the shift lock key in that it capitalizes letters but does not affect other keys, such as numbers or punctuation. Some early computer keyboards, such as the Commodore 64, had a shift lock but no caps lock; others, such as the BBC Micro, had both, only one of which could be enabled at a time.

A version of caps lock that behaves like a traditional shift lock does exist on certain layouts such as the French AZERTY. Some operating systems and window managers allow caps lock to be used for a similar function. This behavior of the caps lock survives, however, in German and Austrian QWERTZ keyboards.

The keyboards of many early computer terminals, including the Teletype Model 33 ASR and Lear-Siegler ADM-3A, and early models of the IBM PC, positioned the Ctrl key where caps lock resides on modern keyboards.

The undesirable attributes of caps lock have led some power users to swap the positions of the two keys using aftermarket modifications; in the same vein, the One Laptop Per Child computers opt to place Ctrl in the caps lock position and discard caps lock entirely. In a similar vein, the Google Cr-48 netbook replaces caps lock with a dedicated “Search” key.