Windows NT Kernel

                                                   Windows NT Kernel
  
Everyone in Know the Linux kernel but don't maximum student don't use it but everyone use windows XP or Windows 7 Now-a-days 8 but don't know the kernel inside it,which is like heart of windows OS.

The architecture of Windows NT, a line of operating systems produced and sold by Microsoft, is a layered design that consists of two main components, user mode and kernel mode. It is a preemptive, re-entrant operating system, which has been designed to work with uniprocessor and symmetrical multi processor (SMP)-based computers. To process input/output (I/O) requests, they use packet-driven I/O, which utilizes I/O request packets (IRPs) and asynchronous I/O. Starting with Windows 2000, Microsoft began making 64-bitversions of Windows available—before this, these operating systems only existed in 32-bit versions.

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 Windows NT kernel is known as a hybrid kernel. The architecture comprises a simple kernel, hardware abstraction layer (HAL), drivers, and a range of services (collectively named Executive), which all exist in kernel mode.

User mode in Windows NT 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 NT: the Environment subsystem (which runs applications written for many different types of operating systems), and the Integral subsystem operates system specific functions on behalf of the environment subsystem. Kernel mode in Windows NT has full access to the hardware and system resources of the computer. The kernel mode stops user mode services and applications from accessing critical areas of the operating system that they should not have access to.

Architecture of Windows NT:

For more :http://en.wikipedia.org/wiki/Architecture_of_Windows_NT