Wikipedia:Today's featured article/August 19, 2007

The architecture of Windows NT is highly modular, and consists of two main layers: a user mode and a kernel mode. Programs and subsystems in user mode are limited in terms of what system resources they have access to, while the kernel mode has unrestricted access to the system memory and external devices. The kernels of the operating systems in this line are all known as hybrid kernels - although it is worth noting that this term is disputed, with the claim that the kernel is essentially a monolithic kernel that is structured somewhat like a microkernel. The architecture comprises a hybrid kernel, Hardware Abstraction Layer (HAL), drivers, and Executive, which all exist in kernel mode. The higher-level services are implemented by the Executive. Kernel mode in the Windows NT line is made of subsystems capable of passing I/O requests to the appropriate kernel mode software drivers by using the I/O manager. Two subsystems make up the user mode layer of Windows 2000: the Environment subsystem (runs applications written for many different types of operating systems), and the Integral subsystem (operates system specific functions on behalf of the environment subsystem). The kernel sits between the Hardware Abstraction Layer and the Executive to provide multiprocessor synchronization, thread and interrupt scheduling and dispatching, and trap handling and exception dispatching. (more...)

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