Understanding the architecture and terminology of Mac OS X is important to be able to use it effectively.
Functionally, the Mac OS X architecture consists of several “layers” that are often shown graphically as in Figure 1.1. The base level of the operating system is its Unix core, which is called Darwin. Moving “up” through the layers, the next layer is the graphics subsystem, which consists of three parts: Quartz, OpenGL, and QuickTime. Then comes the application layer, which has four components, those being Classic, Carbon, Cocoa, and Java. Finally, the top layer is the user interface, which is called Aqua.