Touch screens enable direct tactile and visual interaction between a user and their electronic device. They were invented in the 1960s and found their first widespread usage in the Magnavox Plato IV student terminal at the University of Illinois in 1972.
Touch screens come in two main variants: capacitive and resistive. A capacitive touch screen features an insulating external material, such as glass or plastic, coated with a transparent conductor such as indium tin oxide. Because the human body is also conductive, touching a finger to this screen changes the distribution of an otherwise homogeneous electrostatic field that is sensed at the edges of the screen as a change in capacitance. Sensors pinpoint the location of the placed fingertip through this change in capacitance, registering touch.
A resistive touch screen features electrically resistive layers that are placed parallel to one another with a slight gap in between. The inner layer of the outside resistive layer and the outer layer of the inside layer are coated with a conducting material. A constant voltage is applied between the two layers. When a finger is depressed against the outer layer it causes the two layers to meet, changing the voltage between the two layers, signifying a touch incident. The advantage of the resistive touch screens over their capacitive counterparts is that the former are inherently pressure sensitive.