Most computer companies build only one piece of the puzzle. One company makes an OS. Another company assembles hardware into a box. Yet another company creates software to sell. Still other companies create the APIs and widgets to mix it up with all the other companies' offerings.
While Apple, like all large companies, contracts out pieces of their products and assembles important technologies, they also are in control of the entire product. Apple creates computers from the ground up. Hardware, operating system, and applications are all designed, integrated, and sold by Apple.
This end-to-end control of production gives Apple power to design the best personal computers on the planet. Their operating system is probably Apple's greatest strength. OS X is designed with unparalleled modularity.
Recently Apple did the incredible by moving its whole operating system from PowerPC to Intel architecture without an entire rewrite. Such a change is on the scale of moving a sports arena in one piece to a new city without seeing it collapse. The move was successful in large part because of the modular structure of Mac OS X.
In this chapter, I explain the structure of OS X. I introduce the layers of OS X. I explore Darwin with an emphasis on BSD tools and libraries. ...