All the devices described in this chapter have in common the use of the iOS operating system, originally known as iPhone OS up to version 3. It was developed by Apple specifically for iPhone, iPad, and iPod touch. It was unveiled for the first time in January 2007 and was introduced with the first model of iPhone in June of the same year.
iOS is an operating system based on the older forefather Mac OS X, a derivative of BSD Unix with a Mach kernel XNU based on Darwin OS. It uses the following four levels of abstraction: