Programming in Objective-C, Sixth Edition

Framework Layers

A diagram is often used to illustrate the different layers that separate the application at the topmost level from the underlying hardware. Figure 20.1 depicts one such representation.

Figure 20.1 The application hierarchy

The kernel provides the low-level communication to the hardware in the form of device drivers. It manages the system’s resources, which includes scheduling programs for execution, managing memory and power, and performing basic I/O operations.

As its name implies, Core Services provides support at a lower or “core” level than that provided in the layers above it. For example, here you find support for collections, ...