The A+ Exams Guide: (Exam 220-301), (Exam 220-302) (TestTakers Guides)

A touch screen is a computer display device that reacts to human touch. It can be classified as both an input or output device because it ‘inputs' signals through a controller to a processor and then ‘outputs' or ‘presents' information through a display screen. Touch screens are most often used in such places as kiosks, restaurants, and in some training facilities where the use of a pointing device such as a mouse or a keyboard might prove cumbersome or awkward. Touch screens are typically connected to computer systems through external USB or serial ports.

There are three different types of touch screen technology used today. They are:

• Surface wave: This touch screen technology is by far the most advanced. It uses ultrasonic waves that run across the touch screen. When a particular area of the touch screen is pushed with a finger or touched with a pointing device, such as a stylus, that area is ‘absorbed,' and a signal representing that area is sent to a controller. One drawback to this technology is that it is highly sensitive to outside conditions, such as inclement weather.

• Resistive: This technology uses a metallic layer that is electrically conductive and resistive. When an area on the screen is touched with a finger or stylus, a change occurs in the electrical current present within that area. This electrical change is registered, and an event is passed to the controller for further processing. Resistive technology touch screens are much more affordable than surface wave touch screens, and they are not affected by normal outside weather conditions, such as water. The drawbacks are that resistive displays are substantially less clear to the sight than surface wave or capacitive technology.

• Capacitive: Capacitive technology employs a screen that is covered with a substance or material that stores electrical charges. Electrical sensors (circuits) are located at the corners of the screen. These sensors recognize when an area on the screen has been touched by human contact. They in turn gather the electrical charges registered and forward the collected information to a controller for processing. Capacitive technology provides a good deal of clarity. It is not affected by normal outside conditions, such as dust and weather.