iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone and iPod Touch; it also powered the iPad until the introduction of iPadOS in 2019. It is the world's second-most widely installed mobile operating system, after Android. It is the basis for three other operating systems made by Apple: iPadOS, tvOS, and watchOS.
Unveiled in 2007 for the first-generation iPhone, iOS has since been extended to support other Apple devices such as the iPod Touch (September 2007) and the iPad (January 2010). As of March 2018[update], Apple's App Store contains more than 2.1 million iOS applications, 1 million of which are native for iPads. These mobile apps have collectively been downloaded more than 130 billion times.
The iOS user interface is based upon direct manipulation, using multi-touch gestures such as swipe, tap, pinch, and reverse pinch. Interface control elements include sliders, switches, and buttons. 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 between portrait and landscape mode). Various accessibility functions enable users with vision and hearing disabilities to properly use iOS.
Major versions of iOS are released annually. The current version, iOS 13, was released to the public on September 19, 2019; it brought user-interface tweaks, a dark mode, a redesigned Reminders app, a swipe keyboard, and an improved Photos app. iOS 13 cannot be used by devices with less than 2 GB of RAM, including the iPhone 5s, iPod Touch (6th generation), and the iPhone 6 and iPhone 6 Plus, which as of June 2019 made up more than 10% of iOS devices.