iOS is derived from OS X, with which it shares the Darwin foundation, and is therefore a Unix operating system.
iOS is Appple’s mobile version of the OS X operating system used on Apple computers.
iOS (previously IPhone OS) is a mobile operating system. Developed by Apple Inc. Supports apple devices such as IPhone, IPod Touch, IPad, Apple TV. Originally unveiled in 2007 for the IPhone.
The user interface of iOS is based on the concept of direct manipulation, using multi-touch gestures.
iOS shares with OS X some frameworks such as Core Foundation and Foundation; however, its UI toolkit is Cocoa Touch rather than OS X's Cocoa, so that it provides the UIKit framework rather than the AppKit framework. It is therefore not compatible with OS X for applications. Also while iOS also shares the Darwin foundation with OS X, Unix-like shell access is not available for users and restricted for apps, making iOS not fully Unix-compatible either.
1. IPhone OS 1.0-1.1.5
2. IPhone OS 2.0- 2.2.1
3. IPhone OS 3.0- 3.2.2
4. iOS 4.0- 4.3.5
5. iOS 5.0- 5.1.1
6. iOS 6.0- 6.1.6
7. iOS 7.0-7.1.2
8. iOS 8.0-8.0.2