A touch screen is a computer display screen that serves as an input device. When a touch screen is touched by a finger or stylus, it registers the event and sends it to a controller for processing.
A touch screen may contain pictures or words that the user can touch to interact with the device.
A touch screen has two main advantages. First, it allows users to interact directly with what is displayed, rather than indirectly with a pointer controlled by a mouse or touchpad. Secondly, it does not require the use of an intermediate device. Touch screens can be attached to computers or to networks as terminals. They also play a prominent role in the design of digital appliances such as the personal digital assistant (PDAs), satellite navigation devices, mobile phones and video games.
How a touch screen event is registered depends on the touch screen's inherent technology. The three main touch screen technologies are:
Resistive: This screen has a thin metallic layer that is conductive and resistive, so that touching results in a change in the electrical current sent to the controller. Pros: More affordable, not damaged by dust or water, responds to finger or stylus. Cons: Only 75% clarity and susceptible to damage by sharp objects.
Surface Acoustic Wave (SAW): Ultrasonic waves pass over this screen. Touching it results in absorption of part of the wave, registering the position of the touch, which is sent to the controller. Pros: Responds to finger or stylus. Cons: May be damaged by dust or water.
Capacitive: This screen is coated with an electrically-charged material. Touching it causes a change in capacitance, which allows the location to be determined and sent to the controller. Pros: Not damaged by dust or water and has high clarity. Cons: Must be touched with a finger only - a stylus cannot be used.