While most keyboard keys produce letters, numbers or symbols ( characters), other keys or simultaneous key presses can prompt the computer to execute system commands, such as such as the Control-Alt-Delete combination used with Microsoft Windows. However, producing some symbols may require pressing and holding several keys simultaneously or in sequence. Keyboard keys (buttons) typically have a set of characters engraved or printed on them, and each press of a key typically corresponds to a single written symbol. Replacing early punched cards and paper tape technology, interaction via teleprinter-style keyboards have been the main input method for computers since the 1970s, supplemented by the computer mouse since the 1980s.
A computer keyboard is a peripheral input device modeled after the typewriter keyboard which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches.
