iOS Architecture
![Iphone_os_architecture.png]()
Cocoa Touch Layer
It is a top layer of the iPhone OS stack and it contains the frameworks that are most commonly used by iPhone application developers. Cocoa Touch is primarily written in Objective-C, and it is based on the standard Mac OS X Cocoa API.
Media Layer
It is the second layer from the top of the stack. It provides the iPhone OS with audio, video, animation and graphics capabilities. As with the other layers of the iPhone OS stack, the Media layer comprises a number of frameworks that can be utilized when developing iPhone apps.
Core Services Layer
It is the third layer from the top of the stack. The iPhone Core Services layer provides much of the foundation on which the above layers are built.
Core OS Layer
The Core OS Layer is the bottom layer of the iPhone OS stack and sits directly on top of the device hardware. This layer provides a variety of services including low level networking, access to external accessories and the usual fundamental operating system services such as memory management, file system handling and threads.
iPhone Hardware
Hardware devices are managed by iPhone OS and provides the technologies needed for implementing native applications on the phone. The OS ships with several system applications such as Mail, Safari, Phone, that provide standard services to the user.