A peripheral used to transfer data from the outside world into a computer system. Some input devices are operated directly by the user, e.g. keyboard, mouse, touch screen, joystick, digitising tablet, microphone; others are sensors or transducers which convert external signals into data, e.g. using an ananlog to digital converter (this would also be true of a microphone). Other kinds of inputs are really one half of a bidirectional link with another computer or storage device, e.g. serial line, scsi interface.