Like modern desktop operating systems, iOS uses a graphical user interface, or GUI. However, since it is a mobile operating system, iOS is designed around touchscreen input, rather than a keyboard and mouse. For example, applications, or "apps," can be opened by a single tap, rather than a double-click. Different screens can be viewed by swiping your finger across the screen, rather than clicking on open windows.
Since iOS is designed to be simple and easy to use, it does not include several features found in a traditional operating system. For example, you cannot manage files and folders like you can in Mac OS X or Windows. You also have limited access to iOS system settings. Instead of modifying application preferences from within each program, most settings need to be adjusted within the Settings app. Additionally, while you can run multiple programs at once, you can only view one open program at a time.
While Apple's iOS provides a more basic user interface than Mac OS X, each new version adds more features. For example, iOS 2 provided access to the App Store, which allowed users to download and install third-party apps on their iPhones. iOS 3 added copy and paste functionality and iPad support. iOS 4 was the first version to support multitasking and added the GameCenter feature. iOS 5 introduced the Siri voice assistant (only available on the iPhone 4S), and provided new cloud connectivity features.