A touch screen is the only device which can be classed as both an input and an output device.
It consists of a display monitor that is able to sense the location of a finger touching the screen. The location information is sent to the software currently running so that it can react to the event.
For example, the screen may be showing a graphic image of a shopping cart. Touching the cart image with your finger may cause the software to open up a payment page.
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