What is Touchscreen?
Touchscreen is an input device which emulates mouse. Instead of using a mouse we can directly touch the monitor with our finger/stylus, and at the position of the touch a mouse click is generated. Touchscreen has three main parts: Touchscreen Sensor, Controller and Driver Software.

Touchscreen Sensor
A Touchscreen sensor is a touch responsive surface made up of glass panel. It is fitted over the monitor's screen so that viewable area of the display screen is covered with the responsive area of the glass panel. There are several different touch technologies available in the market, each using a different method to sense a touch. There is an electrical current or signal going through the sensor and touching the screen makes a change in voltage or signal. This voltage change is used to determine the location of the touch to the screen.

Controller
The controller is an interface between touch sensor and the PC. It is a small PC card that takes information from the touch sensor and translates it into information that PC can understand. The controller is installed inside the monitor for integrated monitors or it is cased in a plastic case and is attached externally at the back of the monitor. The controller sends the touch event information to PC. Controllers that can be connected to Serial / COM or USB port are available.

Software Driver
The software driver for the touch screens makes it compatible to work with computer. The controller send the touch event information to the driver and the driver further tells the operating system how to interpret touch event information. Touchscreens drivers are more like mouse drivers, so touching the screen is just same as clicking a mouse. As these are quite similar actions, the touchscreen can work with existing softwares.