Just like Android, iOS needs no formal introduction; however, we will go over some key knowledge factors related to it. iOS or iPhone OS is a mobile operating system which was developed by Apple Inc. and first introduced in June 2007 exclusively for Apple devices:
Figure 11: Devices supported by iOS; source: www.macworld.com
Note that one of the biggest differences between Android and iOS is that Apple designed iOS as an operating system, which was exclusively designed for Apple hardware. On the other hand, Android took more of a platform approach, which dictated a set of requirements and then the phone manufacturers could roll out devices adhering to these requirements. Also, this implies that iOS is closed source whereas Android is open source.
Just like Android, iOS also has a version history starting right from iPhone OS 1 and currently at the time of writing of this book, iOS 10 which was introduced in September 2016:
Figure 12: iOS Device...