iOS (iPhone OS) is developed by Apple for the iPhone operating system. It is mainly to the iPhone, iPod touch and the iPad use. Like its Mac OS X based operating systems, it is also based in Darwin. The system was originally called the iPhone OS, until June 7, 2010 announced that the General Assembly renamed WWDC iOS. iOS system architecture is divided into four levels: the core operating system layer (the Core OS layer), the core service layer (the Core Services layer), the media layer (the Media layer), can touch the floor (the Cocoa Touch layer). System operation takes about 240MB of memory space.