INPUT/OUTPUT DEVICE

any of various devices used to enter information and instructions into a computer for storage or processing and to deliver the processed data to a human operator or, in some cases, a machine controlled by the computer. Such devices comprise the peripheral equipment of modern digital computer systems. Apparatus of this kind with direct connection to a system's central processing unit (q.v.) is said to be on-line; peripheral equipment working independently of it is termed off-line. An input device converts incoming data and instructions into a pattern of electronic signals in binary code (i.e., combinations of 0s and 1s) comprehensible to a digital computer, whereas an output device reverses the process, translating the digitalized signals into a form intelligible to the user. Punched-card and paper-tape readers were once extensively used for inputting but have now been supplanted in large measure by more efficient devices. These include video display terminals consisting of a cathode-ray tube, typewriter-like keyboard, and interactive graphic devices such as a light pen, trackball, or joystick. Other direct entry mechanisms are optical laser scanners (e.g., those used with point-of-sale terminals in retail stores) that can read bar-coded data or optical character fonts; and voice-recognition devices capable of understanding simple verbal commands. Output equipment, some of which can also be used for inputting, includes video display terminals, high-speed printers, console typewriters, and audio response units that convert text and other processed data into spoken words. Certain kinds of auxiliary storage devices, as for example magnetic tape and magnetic disk units, double as input/output devices (see computer memory).