Devices that serve as both input device and output device are termed as I/O devices.
An example of input device is a keyboard. Using the keypad, a user types the data. A keyboard sends electrical signals to the computer system, which is essentially the input. The computer then interprets the signals so that the results can be displayed in the form of text on a monitor. In this example, the text is output. In an another example, a computer sends data to a printer and it generates a printed paper. Here, computer is the input device whereas printer is the output device. The input and output may vary in their nature and form depending upon the mechanism. For example, when a computer sends information into a printer as signals, the input is digitized information whereas its output is a tangible printed paper.
It is important to note that an input device e.g. a mouse or the keyboard of a computer can perform the function of sending information to a computer as input. However, these input devices cannot reproduce or receive any information from the computer as output. It is also noteworthy that the input or output classification of devices is relative to each other. This can be elaborated from the example of a USB inserted in the port of a computer and a lead connecting the computer to a printer. Here, while the computer serves as an output device for the USB in that it generates the signals, the computer plays the role of an input device for the printer because eventually, the text will be printed as output by the printer. A USB flash drive and a CD-RW drive are both examples of I/O devices as both can send as well as receive information from a computer.
To conclude, input devices send information into a system whereas output devices generate its results. Some devices can only be either input devices or output devices whereas others can be both. The status of a device as an input device or an output