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.