Thursday 2 June 2011

ABOUT WINDOWS NT OPERATING SYSTEM

Windows NT is a Microsoft Windows personal computer operating system designed for users and businesses needing advanced capability. NT's technology is the base for the Microsoft successor operating system, Windows 2000. Windows NT (which may originally have stood for "New Technology," although Microsoft doesn't say) is actually two products: Microsoft NT Workstation and Microsoft NT Server. The Workstation is designed for users, especially business users, who need faster performance and a system a little more fail-safe than Windows 95 and Windows 98. The Server is designed for business machines that need to provide services for network-attached computers. The Server is required, together with an Internet server such as Microsoft's Internet Information Server (IIS), for a Windows system that plans to serve Web pages.

32-bit applications run 20% faster on this system than on Windows 95 (assuming both have 32 megabytes of RAM). Since older 16-bit applications run in a separate address space, one can crash without crashing other applications or the operating system. Security and management features not available on Windows 95 are provided. The Workstation has the same desktop user interface as Windows 95.

Windows NT Server: The NT Server is probably the second most installed network server operating system after Novell's NetWare operating system. Microsoft claims that its NT servers are beginning to replace both NetWare and the various UNIX-based systems such as those of Sun Microsystems and Hewlett-Packard. NT Server 5.0. essentially became what was renamed Windows 2000. Notable features of the Windows 2000 products are:

    A fully-customizable administrative console that can be based on tasks rather than files, applications, or users
    A new file directory approach called Active Directory that lets the administrator and other users view every file and application in the network from a single point-of-view.
    Dynamic Domain Name Server (DNS), which replicates changes in the network using the Active Directory Services, the Dynamic Host Configuration Protocol (DHCP), and the Windows Internet Naming Service (WINS) whenever a client is reconfigured.
    The ability to create, extend, or mirror a disk volume without having to shut down the system and to back up data to a variety of magnetic and optical storage media.
    A Distributed File System (DFS) that lets users see a distributed set of files in a single file structure across departments, divisions, or an entire enterprise.
    Close integration with and support for Microsoft's Message Queue Server, Microsoft Transaction Server, and Internet Information Server (IIS).

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, reentrant 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-bit versions 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.[1]

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.

The Executive interfaces, with all the user mode subsystems, deals with I/O, object management, security and process management. 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. The kernel is also responsible for initializing device drivers at bootup. Kernel mode drivers exist in three levels: highest level drivers, intermediate drivers and low level drivers. Windows Driver Model (WDM) exists in the intermediate layer and was mainly designed to be binary and source compatible between Windows 98 and Windows 2000. The lowest level drivers are either legacy Windows NT device drivers that control a device directly or can be a PnP hardware bus.

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