Q. Describe the three main architectural layers of Windows XP?

Answer: (1) The HAL (Hardware Abstraction Layer) creates operating system portability by hiding hardware differences from the upper layers of the operating system. Administrative details of low-level facilities are provided by HAL interfaces. HAL presents a virtual-machine interface that is used by the kernel dispatcher, the executive and device drivers.

(2) The kernel layer provides a foundation for the executive functions and user-mode subsystems. The kernel remains in memory and is never pre-empted. Its responsibilities are thread scheduling and interrupt and exception handling low-level processor synchronization and power failure recovery.

(3) The executive layer provide a set of services used by all subsystems object manager virtual memory manager or process manager and local procedure call facility as well as I/O manager, security monitor and plug-and-play manager or registry and booting.