For many programmers, a kernel just exists. A kernel's internals becomes important to their everyday lives when they need to speed up an application, analyze large amounts of data, or write a sophisticated GUI. In the case of OS X and iOS, most application programmers would profit from an understanding of the kernel, since the design and structure of OS X and its mobile descendants is such that a programmer can tailor applications to the way the kernel manages systems resources. Being able to partition the kernel in your mind and understand the workings of what is called the Mach kernel that actually runs OS X permits sophisticated design decisions and informed system architecture. The layers of OS X have been around for longer than OS X itself, and they were folded into and tuned to the amazing experience OS X provides. Jonathan Levine starts off by explaining the evolution of OS X, which is vital if we are to understand the components of Apple's operating systems and their purpose. He then proceeds to delve into the core of Mac OS X, throwing light on what's going on under the surface of the Mac or the iPhone. This helps to explain the boot-up sequence, which should be of interest to system administrators and serious users alike. The reader then learns why the kernel and its layers work so well on the Mac by making clear what the different layers actually do. Filesystems and the networking stack make direct use of OS X architectural components, thereby clearly demonstrating the logic of OS X and iOS design. This is vital information for system administrators and system architects. Finally, programmers learn to write kernel extensions. This is perhaps what C programmers will be most interested in, and what any Cocoa programmer needs to know. System administrators and system architects will also profit from insight into the actual workings of independently coded OS X components. What you'll learn Learn OS X and kernel boot-up sequence Distinguish the roles of different OS X and iOS layers Influence OS X kernel behavior Start writing kernel extensions Gain a clear appreciation of OS X filesystems Who this book is for OS X system administrators will need this book in their arsenal, but system architects and programmers will strongly benefit from a clear understanding of the architecture of OS X and iOS. Application programmers interested in highly performant applications running on OS X or iOS directly should be interested as well.