Beginning iOS 5 Application Development

ARCHITECTURE OF THE IOS

Although this book doesn't explore the innards of iOS, understanding some of its important characteristics is useful. Figure 1-13 shows the different abstraction layers that make up the Mac OS X and iOS (which is used by the iPhone, iPod touch, and iPad).

NOTE The iOS is architecturally very similar to the Mac OS X except that the topmost layer is Cocoa Touch for the iPhone, rather than the Cocoa Framework.

FIGURE 1-13

The bottom layer is the Core OS, which is the foundation of the operating system. It is in charge of memory management, the file system, networking, and other OS tasks, and it interacts directly with the hardware. The Core OS layer consists of components such as the following:

• OS X Kernel
• Mach 3.0
• BSD
• Sockets
• Security
• Power Management
• Keychain
• Certificates
• File System
• Bonjour

The Core Services layer provides an abstraction over the services provided in the Core OS layer. It provides fundamental access to iOS services and consists of the following components:

• Collections
• Address Book
• Networking
• File Access
• SQLite
• Core Location
• Net Services
• Threading
• Preferences
• URL Utilities

The Media layer provides multimedia services that you can use in your iPhone and iPad applications. It consists of the following components:

• Core Audio
• OpenGL
• Audio ...