Three important features generally characterize the interaction of a computer system with its users: input, processing, and output. Input and output (sometimes referred to as input/output or simply I/O) refers to the transfer of information back and forth within a computer system. Individually, input involves the information that is gathered and entered into the central processing unit (CPU) for processing, and output involves the information that is subsequently processed through the CPU and exited so that it can be made available (and useful) to computer users.

Information that is considered input can take a variety of forms, such as commands from a user at a keyboard (sometimes with the help of a mouse), information from another computer or device, or information from a file stored on a disk drive. Devices that help to input data into the computer are generically called "input...