IOS(originally iPhone OS) is a mobile operating system created and developed by Apple Inc. and distributed exclusively for Apple hardware. It is the operating system that presently powers many of the company’s mobile devices, including the iPhone, iPad, and iPod touch. Major versions of iOS are released annually. The current release, iOS 9.2, was released on December 8, 2015. 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 the operating system(iOS 9), dedicates around 1.3 GB of the device’s flash memory for iOS itself. It runs on the iPhone 4S and later, iPad 2 and later, iPad Pro, all models of the iPad Mini, and the 5th-generation iPod Touch and later. This site provides the best course about iOS 9 and its features.