Input and output devices allow a computer to communicate with the external world by receiving and transmitting data. Input devices such as keyboards, mice, and scanners transfer data into the computer, while output devices like monitors, printers, and speakers share the results of processed data. There are two main types of input devices - manual devices that are operated by hand, and direct data entry devices that can quickly input large amounts of data automatically. Common output devices display visual information on screens or print hard copies. The monitor is a crucial output device that shows users pictures, videos, and graphics on its screen.