A touchscreen is a display that also serves as an input device. Some touchscreens require a proprietary pen for input, though most modern touchscreens detect human touch. Since touchscreen devices accept input directly through the screen, they do not require external input devices, such as mice and keyboards. This makes touchscreens ideal for computer kiosks, as well as portable devices, such as tablets and smartphones.
While a touchscreen may look like an ordinary display, the screen includes several extra layers that detect input. The first layer is a hard protective layer that protects the actual display and the touchscreen components. Beneath the protective layer is an electronic grid that detects input. Most modern touchscreens use capacitive material for this grid, in which the electrical charge changes wherever the screen is touched. Beneath the touchscreen layer is the LCD layer, which is used for the actual display.
While early touchscreens could only detect a single point of input at a time, modern touchscreens support "multi-touch" input. This technology, which was made popular by the original iPhone, enables the screen to detect multiple finger motions at once. For example, on some touchscreen devices, you can rotate an image by twisting three fingers in a clockwise or counterclockwise motion. Many touchscreen applications also allow you zoom in and out by spreading two fingers apart or pinching them together.
Thanks to multi-touch and other improvements in touchscreen technology, today's touchscreens are easier and more natural to use than they used to be. In fact, improved touchscreen technology has greatly contributed to the popularity of the iPad and other tablet PCs.