Which can be the input and output devices both?

Most devices connected to a computer are classified as either input devices, which send data into the computer, or output devices, which present data from the computer to the user. A device that can do both must physically accept data from the user and also display data to the user through the same surface.

A touch screen monitor does exactly this. As a monitor, it displays images, text, and video generated by the computer, which makes it an output device. At the same time, its touch-sensitive surface detects the position and pressure of a finger or stylus and sends that positional data back into the computer, which makes it an input device as well.

A scanner and a digitizer only capture data from the physical world into the computer, so they are input-only devices. A speaker only converts electrical signals into sound for the user to hear, so it is output-only. None of these three can also receive commands or data from the user through the same interface.

Examination reminder: a device qualifies as both input and output only when the same physical component performs both roles, as the touch screen does by displaying and sensing touch simultaneously.