This presentation discusses the operating systems used in smartphones. It begins with a definition of smartphones and their key features. The history of smartphone OS is then reviewed, including Symbian in 2000, iOS in 2007, Android in 2008, and Windows Phone. The presentation focuses on the three main OS - Android, iOS, and Windows Phone. It provides details on each OS like its programming languages and number of available apps. It concludes with a comparison of the current versions of the three OS.