OS X and iOS Kernel Programming

The Role of the Operating System

As part of the boot sequence, the operating system determines the hardware configuration of the system, finds any external devices connected to USB ports or plugged into PCI expansion slots, and initializes them, loading drivers along the way, if necessary.

Once the operating system has completed loading, the user is able to run application software. Application software may need to allocate memory or write a file to disk, and it is the operating system that handles these requests. To the user, the involvement of the operating system is largely transparent.

The operating system provides a layer of abstraction between running applications and the physical hardware. Applications typically communicate with hardware ...