WINDOWS NT SERVER ARCHITECTURE

Windows NT Server contain various components among which some of the components run in user mode and other run in kernel mode. Kernel Mode is a
special type of mode in which all the hardware and system data can be accessed by  the running code,
whereas in user mode, there in only restricted access to the system data and hardware by the running code. The user mode is also referred to as non-privileged mode. The architecture of Windows NT Server contains the following components :

• Hardware Abstraction Layer (HAL)
• Kernel
• NT Executive
• Protected Environment Subsystems

Hardware Abstraction Layer (HAL)

HAL is a software interface located between the hardware and the operating system and it is the lowest level

component of the Windows NT operating system. HAL is platform-specific and carries cods for communication and controlling the hardware on which Windows NT operates. HAL gives the interface for

Symmetric MultiProcessing (SMP) and enable Windows NT Server more application-friendly.

HAL is executed as a Dynamic Link Library (DLL) and, is responsible for protecting Windows NT server based on HAL is that it is not compatible with the older version of DOS and Windows program : 

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CLASSIFICATION OF OPERATING SYSTEMS

All operating systems consist of  similar components and perform  almost similar functions but the methods and procedures for performing these functions are different. Operating systems are classified into following different categories based on their distinguishing features: 

• Single -user Operating system
• Multi-user Operating system
• Batch processing Operating system
• Multiprogramming Operating system
• Multitasking Operating system 
• Parallel Operating system
• Distributed Operating system
• Real.time operating system

Single-User Operating System 

It allows a single user to access a computer at a time . These computer have single processor and execute 

single program . The resources such as CPU and I/O device are constantly available to the user in a single 

user operating system for operating the system. As a result, the CPU site idle for most of the time and is not utilised to it maximum. A single -user OS is divided into categories :

• Single-user, single-tasking operating system
• single-user , multi-tasking operating system

The single-user, single-tasking operating system allows a single-user to execute on

program at a time. MS-DOS and palm OS for palm hand-held computer at

examples of single-user single-tasking operating system .

Single-user multitasking operating system allows a single-user to operate multiple programs at the same time. For example, you can perform calculation in Excel sheet print a Word document and download a file from the internet concurrently .

Mac OS Windows 95, Windows 98, Windows NT Workstation and Windows 2000 Professional, operating system for desktop and laptop computer are the examples of single-user, multi-tasking operating system. 

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