A tablet computer is a personal mobile computer which is used most of the time by tapping with a finger or a stylus on a touch screen. It is bigger than a mobile phone but smaller than a laptop. Its main functions are to display books, movies, games, maps, web sites, or to play music. Tablet computers include the Samsung Galaxy and the iPad. Most tablet computers use Android, originally a smartphone operating system. Some use iOS. A few use desktop operating systems such as Windows or Ubuntu.