Computers are obsessed over the two letters I and O. I/O stands for Input and Output, which are the two things a computer does best. Really, I/O is pretty much the only thing a computer does. You get this whole I/O concept down and you’ve tackled the essence of what a computer is and what it can do. The devices connected to your computer are divided into input and output camps:
Input devices: The computer receives information from input devices. The keyboard and mouse are two input devices, as are a scanner and a digital camera. They all send information to the computer.
Output devices: The computer sends information from output devices. Output is simply anything the computer produces. The stuff displayed on the monitor is output, sound is output, and the pages the computer prints are output. The monitor, speakers, and printer are all output devices.
Devices that both input and output: Some devices can do both input and output. For example, a disk drive can supply input to the computer as well as store output. A modem both sends and receives information.