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iOS (formerly iPhone OS) is Apple's mobile operating system family. Originally developed for the iPhone, it has since been extended to support other Apple, Inc. devices such as the iPod Touch, iPad, and Apple TV. Apple, Inc. does not license iOS for installation on non-Apple hardware. As of October 4, 2011, Apple, Inc.'s App Store contained more than 500,000 iOS applications, which have collectively been downloaded more than 18 billion times. It had a 26% share of the smartphone operating system units sold in the last quarter of 2010, behind both Google's Android and Nokia's Symbian. In May 2010 in the United States, it accounted for 59% of mobile web data consumption (including use on both the iPod Touch and the iPad).
The user interface of iOS is based on the concept of direct manipulation, using multi-touch gestures. Interface control elements consist of sliders, switches, and buttons. The response to user input is immediate and provides a fluid interface. Interaction with the OS includes gestures such as swipe, tap, pinch, and reverse pinch, all of which have specific definitions within the context of the iOS operating system and its multi-touch interface. Internal accelerometers are used by some applications to respond to shaking the device (one common result is the undo command) or rotating it in three dimensions (one common result is switching from portrait to landscape mode).
iOS is derived from macOS, with which it shares the Darwin foundation, and is, therefore, a Unix-like operating system by nature, as Darwin is based on the BSD family of Unix-like operating systems. The file system used by iOS by default is case-sensitive.
In iOS, there are four abstraction layers: the Core OS layer, the Core Services layer, the Media layer, and the Cocoa Touch layer. The current version of iOS is currently version 11.4.
Game Center is an online multi-player social gaming network released by Apple. It allows users to invite friends to play a game, start a multi-player game through matchmaking, track their achievements, and compare their high scores on a leaderboard. Game Center was originally announced on April 8, 2010, and became publicly available with the release of iOS 4 on September 8 of that year. With a major update to the service in October 2011, it is officially available for iOS devices capable of running iOS 4.2 or later. The app does not come standard with the current iOS but parts of the service come standard with the current iOS.