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In [[The Anatomy of an iPhone 4 (iOS4 iOS 4 Xcode 4)|The Anatomy of an iPhone 4]] we looked at the hardware that is contained within an iPhone 4 device. When we develop apps for the iPhone Apple does not allow us direct access to any of this hardware. In fact, all hardware interaction takes place exclusively through a number of different layers of software that act as intermediaries between the application code and device hardware. These layers make up what is known as an operating system. In the case of the iPhone, this operating system is known as iOS.
In order to gain a better understanding of the iPhone development environment, this chapter will look in detail at the different layers that comprise the iOS operating system and the frameworks that allow us, as developers, to write iPhone applications.
