Differentiate input device from output device?

Answer 1

An input device is any piece of hardware that allows data (in any form) into a computer: a keyboard, a camera, a scanner are all input devices. (input = put in) An output device is any piece of hardware that allow users (us) to either see or remove data from a computer: monitors and printers are output devices. (output = put out)

Answer 2

an input device is something that interfaces with a human user to accept data (mouse, keyboard, scanner)

output is a device that gives information back to the human (monitor , printer)