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Windows NT A Distributed Architecture. Professor: Mohamed Khalil CSE 8343 GROUP-A5 Dhaval Sanghvi Amit Sharma Ali Abbas (Video-Tape). Agenda. Features

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Windows nt a distributed architecture
Windows NT A Distributed Architecture

Professor: Mohamed Khalil

CSE 8343


Dhaval Sanghvi

Amit Sharma

Ali Abbas (Video-Tape)


  • Features

  • Design goals of Windows NT

  • Architecture

    • Three Layers

      • Upper Layer - Executive

      • Middle Layer - Kernel

      • Lower Layer - Hardware Abstraction Layer

  • Environment Subsystem

  • Summary

  • Biblography


  • Preemptive Multitasking

  • Support for Symmetric Multiprocessing

  • Integrated Networking services

  • Client/Server Architecture

  • Support for several file systems

  • Virtual Memory Management

  • Support for 2 GB linear space for application and also 2GB for OS

Design goals of windows nt
Design goals of Windows NT

  • Extensibility

  • Portability

  • Reliability

  • Compatibility

  • Security

  • Performance

  • Scalability

  • Localization

Windows nt architecture
Windows NT Architecture

  • Windows NT is a modular operating system

    composed of simple modules : kernel mode and user mode.

  • Kernel Mode composed of mainly 3 layers:

    • Upper layer - Executive layer

    • Middle layer - The kernel

    • Lower layer - Hardware Abstraction Layer(HAL)

  • User Mode is composed of environment subsystems.

Executive layer
Executive Layer

  • Each component of NT Executive provides a set of API’s

  • Some API’s are designed to be invoked by user-mode processes.

  • Some API’s are visible only in the kernel mode inside the Executive

  • NT’s API’s are flexible enough to implement a wide range of operating system environments.

  • NT’s Executive has six subsystems - Object Manager, Process Manager, Virtual Memory Manager, Security Reference Monitor, Local Procedure Call Facility, I/O subsystem

Object manager
Object Manager

  • An object is a representation of a conceptual or physical entity in the system.

  • Examples of Objects:

    • Files

    • Directories

    • Processes

    • Threads

    • Synchronization Objects (semaphores, mutexes, events, timers)

    • Virtual Memory objects

  • Mostly everything passed around and processed within NT is represented as an object.

Security reference monitor
Security Reference Monitor

  • Checks for proper authorization before granting access to objects

  • Object Manager is a customer of a SRM: it asks SRM if a process has the proper rights to execute a certain type of action on an object.

  • Implements auditing functions to keep track of attempts to access an object

  • Implements high level security:

    • Resource owners must be able to control who has access to it.

    • Unique user name and password identification

    • Audit trail of successful and unsuccessful attempts

    • Protection from unauthorized tampering of files

Process manager
Process Manager

  • Creates,deletes and modifies processes and threads

  • Does not dispatch or schedules any work. This is done by the kernel

  • A process is represented within NT by a process object

  • Process Object = (process’ virtual address space, resources visible to the process, process threads)

  • NT does not maintain parent-child information between related processes.

Virtual memory manager vmm
Virtual Memory Manager(VMM)

  • Implements a fetch policy(when the pager brings a page from disk to memory). Uses a demand paging algorithm with the locality of reference(“clustering”)

  • Implements shared memory segments(used by LPC to transfer large messages)

  • Certain parts of the VMM are processor dependent (e.g. page table entries,page size,virtual address translation)

  • Manages file system drivers,device drivers and network drivers

Vmm cont d
VMM - cont’d

  • Drivers can be dynamically loaded, unloaded, started and stopped without rebooting the system

  • Multiple installable file systems including MS-DOS FAT ( File Allocation Table), High Performance File System(HPFS), the CD-ROM file system and the NT File System(NTFS)

I o manager
I/O Manager

  • Mapped file I/O capabilities for image activation, file caching and application use

  • Packet driven I/O system. Every I/O request is represented by an IRP (I/O Request Packet) that moves from one I/O system component to the other

  • Manages buffers for I/O requests

  • Provides time-out support for drivers

  • Records which installable components are loaded in the system

I o manager cont d
I/O Manager - cont’d

  • NTFS extends MS-DOS FAT with HPFS with:

    • Quick recovery of disk data after system failure

    • Ability to handle very large files (17 billion GB)

    • Security features (e.g. execute only files)

    • Support for POSIX OS environments

    • Features for future extensibility(e.g. transaction-based operations to enhance fault tolerance,user-controlled file version numbers, flexible options for file naming and file attributes)

Kernel layer
Kernel Layer

  • Schedules threads to run.

  • Handles hardware interrupts and dispatches them to appropriate drivers and threads.

  • Handles software and hardware generated exceptions (e.g. writing to non-existing memory position, memory parity errors)

  • Graceful system shutdown and restoration after power failure

  • Provides an API to the executive to kernel-managed objects (e.g. events, mutexes, semaphores and timers)

Hardware abstraction layer
Hardware Abstraction Layer

  • Isolates the kernel from hardware variations

  • Exports an API to upper layers to handle hardware dependent issues such as:

    • Processor initialization( support for SMP computers)

    • Instruction cache and data cache

    • Device driver support(e.g. bus addressing, interrupt control, DMA functions)

    • Timing and interrupt functions

    • Firmware interface functions

    • Low level error handling

Environment subsystem
Environment subsystem

  • User mode process that provides services to applications

  • These services emulate the behavior of a specific OS

  • Converts requests made by an application to requests that NT’s kernel mode component understand

  • Implemented using Client/Server model:

    • Application Client

    • Environment subsystem Server

Win32 subsystem
Win32 Subsystem

  • Implements the Win32 API

  • Each Win32 application runs on its own address space separate from Win32 subsystems’ address space

  • Manages all the keyboard and mouse input and all screen output for entire system

    acts as a server to the other environment subsystems

Os 2 subsystem
OS/2 Subsystem

  • Supports OS/2 up to 1.3 character-mode applications

  • Each OS/2 application runs on its own separate address space and separate from the OS/2 subsystem’s address space

    POSIX Subsystem

  • Supports POSIX character-mode applications

  • Each POSIX application runs on its own separate address space and separate from POSIX subsystem’s address space

Ms dos environment
MS-DOS Environment

  • Associates each DOS application with Virtual DOS Machines (VDM)

  • Each DOS applications runs on its own address space

  • A VDM provides the DOS application with:

    • Execution of Intel x86 instructions

    • Simulated DOS INT 21 services

    • Simulated DOS BIOS interrupt services

    • Simulated standard PC hardware devices

Windows 16 bit environment
Windows 16-Bit Environment

  • All Win16 applications are supported by a single VDM called WOW (Win16 on Win32)

  • WOW is like a virtual windows machine

  • The WOW runs on an address space separate from all other user level processes

  • A WOW emulates a PC as a DOS VDM does

  • WOW converts Win16 API’s and messages to and from Win32

  • The Win32 subsystem is used to execute the translated calls

Win 16 bit environment cont d
Win 16-Bit Environment – cont’d

  • Each Win16 application is assigned to a different thread within the WOW VDM process

  • Each such thread must yield control before another thread of the WOW is allowed to run

  • If Win16 application crashes it may take the whole WOW down but it does not affect the other Win 32 applications



  • Windows NT server 4.0 Administrator’s Bible, R.Cowart and K.Gregg, IDG Books

  • Inside Windows NT Workstation, George Eckel, New Riders, 1996.