Any idea what makes you close programs in Android phone by simply swiping them away? Or allowing you to tap on the screen to open a program, pinch your fingers together to minimize or enlarge an image, or swipe your finger across the screen to change pages in an iPhone? Or the tile-based interface – dubbed Metro – in a Windows Phone? All this is possible because of “Mobile OS (Operating System)”. A mobile OS is specifically designed to run on mobile devices such as mobile phones, smartphones, PDAs, tablet computers and other handheld devices.