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Understanding Operating Systems
Sixth Edition
Chapter 15
Windows Operating Systems
Learning Objectives
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After completing this chapter, you should be able to
describe:
The design goals for Windows operating systems
The role of MS-DOS in early Windows releases
The role of the Memory Manager and Virtual
Memory Manager
The use of the Device, Processor, and Network
Managers
System security challenges
The Windows user interface
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Windows Development
• First Windows product communication method
– Graphical user interface (GUI)
• Primary user communication method
• Needed underlying operating system to translate users’
requests into system commands
• Windows 1.0 (1985)
– First Windows application
– Ran on PC-compatible microcomputers
– Not a true operating system
• Ran on top of MS-DOS
• Interface between MS-DOS and user
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Early Windows Products
• Advancements in Windows
– Increasingly sophisticated GUI design
• Increasingly powerful desktop computers
• Windows 3.1
– Standardized look and feel
• Similar to Apple’s Macintosh computer
– Entry level product
• Single-user installations or small-business
environments
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Early Windows Products (cont'd.)
• Windows for Workgroups
– Accommodate network users’ needs (small business)
• Programs and features for small LANs
• Share directories, disks, printers
• Personal intercommunication: e-mail, chat programs
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Operating Systems for Home and
Professional Users
• Disadvantages running Windows on MS-DOS
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Little built-in security
No multitasking
No interprocess communication capability
Difficulty moving MS-DOS to other platforms
• MS-DOS worked closely with hardware
• Microsoft response
– Developed and released succession of Windows
• Not mere GUIs; had home and office user appeal
– Development of powerful networking products
• Windows NT (New Technology)
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Operating Systems for Home and
Professional Users (cont'd.)
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Operating Systems for Networks
• Windows NT Development (1993)
– No reliance on MS-DOS support
– Primary market requirements
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Portability
Multiprocessing capabilities
Distributed computing support
Government procurement compliance requirements
Government security certification
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Operating Systems for Networks
(cont'd.)
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Operating Systems for Networks
(cont'd.)
• Windows NT versions
– Windows NT Workstation
• Individuals
• Desktop operating system
– Windows NT Server
• Small to medium-sized offices
• Web servers and off-site locations
– Windows NT Server Enterprise Edition
• Larger and more complex networks
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Operating Systems for Networks
(cont'd.)
• Windows NT name changed (1999)
• Windows 2000 four packages
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Windows 2000 Professional
Windows 2000 Server
Windows 2000 Advanced Server
Windows 2000 Datacenter Server
• Windows Server 2003
– Same four packages plus Web edition
• Windows Server 2008 Release 2 (2009)
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Design Goals
• Fulfilling marketing requirements
– Incorporate security features
– Facilitate decision making (coding process)
• Windows networking operating systems
– Influenced by several operating system models
• Use already-existing frameworks
• Introduced new features
– Object model
• Manage and allocate resources
• Symmetric multiprocessing (SMP)
• Maximum multiprocessor performance
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Design Goals (cont'd.)
• Needs
– Accommodate user needs
– Optimize resources
• Response
– Five design goals
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Extensibility
Portability
Reliability
Compatibility
Performance
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Extensibility
• Easily enhancing operating system
• Ensuring code integrity: separate functions
– Privileged executive process
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Kernel mode
Processor’s mode of operation
All machine instructions allowed
System memory accessible
– Nonprivileged processes “protected subsystems”
• User mode
• Certain instructions not allowed
• System memory not accessible
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Extensibility (cont'd.)
• Four more features
– Modular structure
• New components added to executive process
– Objects
• Abstract data types manipulated by special services
• System resources managed uniformly
– Drivers
• New file systems, devices, and networks added to
system at any time
– Remote procedure call
• Application calls remote services
• Regardless of location on network
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Portability
• Operate on different machines
– Different processors or configurations
– Minimum amount of recoding
• System guidelines to achieve goal
– Written in a standardized, high-level language
• Available in all machines
– Accommodated ported hardware
– Minimized direct code interaction with hardware
• Reduced incompatibility errors
– Hardware-dependent code isolated into modules
• Easily modifiable when ported
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Portability (cont'd.)
• Windows NT and successors’ features
– Modular code
– Written in C (most of code)
– Hardware abstraction layer (HAL)
• Dynamic-link library
• Provides isolation from vendors’ hardware
dependencies
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Reliability
• Robustness of system
• Ability to protect itself and users
– Accidental or deliberate user programs’ damage
• Features strengthening system
– Structured exception handling
– Modular design
– NTFS file system (NT file system)
• Can recover from all error types
– Advanced security architecture
– Virtual memory strategy
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Compatibility
• Execute programs written for other operating
systems (or earlier system versions)
– Use protected subsystems
• Provide application execution different from primary
programming interface
– Provides source-level POSIX application compatibility
– Recent Windows versions
• Support existing file systems
• FAT, CDFS, NTFS
– Built-in verification
• Important hardware and software
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Performance
• Achieve good performance levels
• Windows features
– Testing and optimization system calls, page faults,
crucial processes
– Incorporate local procedure call (LPC): guarantee fast
communication among protected subsystems
– Maximize speed of frequently used system services
– Critical Windows networking software elements built
into operating system privileged portion
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Memory Management
• Every operating system
– Has own physical memory view
– Makes application programs access memory in
specified ways
• Full physical memory
– Virtual Memory Manager pages some memory
contents to disk
• Challenge for all Windows operating systems
– Run application programs (Windows, POSIX)
• Without programs crashing into each other’s memory
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Memory Management (cont'd.)
• Memory layout (recent Windows versions)
– Operating system: high virtual memory
– User code and data: low virtual memory
• User process
– Cannot read or write system memory directly
• Memory paged to disk
– User-accessible memory
– System memory segment labeled paged pool
• Memory never paged to disk
– System memory segment labeled nonpaged pool
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Memory Management (cont'd.)
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User-Mode Features
• VM Manager (virtual machine manager)
– User-mode subsystems share memory efficiently
– Provides process services to manage virtual memory
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Allocate memory in two stages
Read and/or write protection for virtual memory
Lock virtual pages in physical memory
Retrieve information about virtual pages
Protect virtual pages
Rewrite virtual pages to disk
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Virtual Memory Implementation
• VM manager reliance
– Address space management
– Paging techniques
• Address space management
– Upper half of virtual address space
• Accessible only to kernel-mode processes
– Code in lower part (kernel code and data)
• Never paged out of memory
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Virtual Memory Implementation
(cont'd.)
• Paging (VM manager is pager)
– Transfers pages
• Between memory page frames and disk storage
– Complex combination
• Software policies: when to bring a page into memory
and where to put it
• Hardware mechanisms: exact manner VM Manager
translates virtual addresses into physical addresses
– Pager not portable
– Windows: small code and well isolated
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Virtual Memory Implementation
(cont'd.)
• Paging policies
– Dictate how and when paging done
– Composition
• Fetch policy: determines when pager copies a page
from disk to memory
• Placement policy: determines where virtual page is
loaded in memory
• Replacement policy: determines which virtual page is
removed from memory to make room for a new page
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Processor Management
• Windows
– Preemptive-multitasking, multithreaded operating
system
• Windows NT process
– Requires at least one thread
• Default
– Process contains one thread
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Processor Management (cont'd.)
• Thread composition
– A unique identifier
– Contents of volatile set of registers indicating
processor’s state
– Two stacks used during thread’s execution
– Private storage area: used by subsystems and
dynamic-link libraries
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Processor Management (cont'd.)
• Threads
– Thread components called thread’s context
– Actual data forming context varies from one
processor to another
– Kernel
• Schedules threads for execution on a processor
– Thread actually executes code
– Overhead incurred by thread is minimal
– Unitasking
• Process with single thread
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Processor Management (cont'd.)
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Processor Management (cont'd.)
• Multithreading using multitasking
– Systems with multiple processors
• Process has as many threads as CPUs available
• All threads belonging to one process: share global
variables, heap, environment strings
• Versions of Windows since NT
– Include some synchronization mechanisms
• Avoid problems with multiple threads
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Processor Management (cont'd.)
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Device Management
• Windows NT I/O system and networking
descendents provide:
– Multiple installable file systems (FAT, CDFS, NTFS)
– Services making device-driver development easy
• Workable on multiprocessor systems
– Adding drivers to the system (system administrators)
• Remove them dynamically
– Fast I/O processing
• Drivers written in high-level language
– Mapped file I/O capabilities
• Image activation, file caching, application use
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Device Management (cont'd.)
• I/O system
– Packet driven
• I/O request represented by I/O request packet (IRP)
– IRP
• Data structure controlling how I/O operation processed
at each step
• I/O manager IRP creation
– Creates an IRP representing each I/O operation
– Passes IRP to appropriate driver
– Disposes of packet when operation complete
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Device Management (cont'd.)
• Driver IRP receipt
– Performs specified operation
– Passes it back to I/O manager or
– Passes it through I/O manager to another driver for
further processing
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Device Management (cont'd.)
• I/O manager tasks
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Supplies code, common to different drivers
Manages buffers for I/O requests
Provides time-out support for drivers
Records installable file systems loaded into operating
system
– Provides flexible I/O facilities
• Subsystems (POSIX) implement their respective I/O
application programming interfaces
– Allows dynamic loading of device drivers and file
systems
• Based on users’ needs
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Device Management (cont'd.)
• Windows I/O services
– Device-independent model
• “Multilayered device driver” concept
• Device driver made up of standard set of routines
– Initialization routine, dispatch routine, start I/O routine,
completion routine, unload routine, error logging
routine
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Device Management (cont'd.)
• I/O manager
– Determine driver called to process request
• Using file object’s name
– Driver object
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Represents individual driver in system
I/O manager creates
Created when driver loaded into system
May have multiple device objects connected to it
– Device object
• Physical, logical, or virtual device on the system
• Describes device characteristics
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Device Management (cont'd.)
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Device Management (cont'd.)
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Device Management (cont'd.)
• Device objects list
– Represents physical, logical, virtual devices
– Controlled by the driver
• Advantages of using different objects
– Portability
• Frees I/O manager from knowing details about drivers
• Follows pointer to locate driver
– Easy loading of new drivers
– Easy assigning drivers to control additional or
different devices
• If system configuration changes
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Device Management (cont'd.)
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Device Management (cont'd.)
• I/O manager knows nothing about file system
• Overhead
– I/O manager passes information requests back and
forth
– Uses single-layer device driver approach
• Simple devices (serial and parallel printer ports)
– Uses multilayered approach
• More complicated devices (hard drives)
• I/O operations asynchronous
– Almost all low-level operations
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File Management
• Windows current versions
– Designed to be independent of file system on which
they operate
– Support multiple file systems for hard disks including:
• MS-DOS’s FAT file system
• 32-bit FAT file system
• NTFS
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File Management (cont'd.)
• Virtual file
– Primary file handling concept (current windows)
– Programs perform I/O on virtual files
• File handles manipulate them
– Executive file object representing all sources and
destinations of I/O
• Processes call native file object services to read
from or write to file
• I/O manager directs virtual file requests
– Real files, file directories, physical devices
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File Management (cont'd.)
• File objects
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Hierarchical names
Protected by object-based security
Support synchronization
Handled by object services
• Opening file
– Process supplies file’s name and type of access
required
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File Management (cont'd.)
• File objects bridge gap
– Between physical devices’ characteristics and
directory structures, file system structures, data
formats
• Provides memory-based representation of shareable
physical resources
• Created with new set of handle-specific attributes
– Each time process opens a handle
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File Management (cont'd.)
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File Management (cont'd.)
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File Management (cont'd.)
• Mapped file I/O
– Important feature of I/O system
– Achieved by cooperation with I/O system and VM
Manager
– Memory-mapped files exploit VM capabilities
• Cache manager uses mapped I/O
– Manages its memory-based cache
• File management system supports long filenames
– Include spaces and special characters
– Automatically shortens filenames when required
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Network Management
• Networking
– Integral to Windows NT-based operating systems
– Provides services
• User accounts, resource security
• Communication between computers
– Named pipes
• Provide high-level interface for passing data between
two processes (regardless of locations)
– Mailslots
• Provide one-to-many and many-to-one communication
mechanisms
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Network Management (cont’d.)
• Microsoft Networks (MS-NET)
– Released in 1984
– Model for NT Network Manager
• Three components
– Redirector
– Server message block (SMB) protocol
– Network server
• MS-NET components
– Extensively refurbished and incorporated into
Windows NT and later versions
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Network Management (cont'd.)
• Redirector
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Coded in C programming language
Implemented as loadable file system driver
Not dependent on system’s hardware architecture
Function
• Direct I/O request from user or application to remote
server that has appropriate file or resource
• Network can incorporate multiple redirectors
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Network Management (cont'd.)
• SMB Protocol
– High-level specification
• Formatting messages sent across network
– OSI model correlation
• Application layer (layer 7)
• Presentation layer (layer 6)
– API called NETBIOS interface
• Used to pass I/O requests structured in SMB format to
remote computer
– SMB protocols and NETBIOS API
• Adopted in several networking products before
appearing in Windows
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Network Management (cont'd.)
• Windows Server operating systems
– Written in C
• Complete compatibility with existing MS-NET and LAN
manager SMB protocols
– Implemented as loadable file system drivers
– No dependency on hardware architecture
• Where operating system running
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Directory Services
• Active Directory
– Database storing all information types
– General-purpose directory service for heterogeneous
network
– Built entirely around DNS and LDAP
– Groups machines into administrative units called
domains
• Each domain gets a DNS domain name (e.g., pitt.edu)
• Each domain must have at least one domain controller
• Domain can have more than one domain controller
– Active Directory clients use standard DNS and LDAP
protocols to locate objects on the network
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Directory Services (cont'd.)
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Security Management
• Windows network operating systems
– Provide object-based security model
– Security object
• Represent any resource in system (file, device,
process, program, or user)
– Allows administrators to give precise security access
• To specific objects in system allowing them to monitor
and record how objects used
• Windows biggest concern
– Aggressive patch management needed
• Combat many viruses and worms
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Security Basics
• U.S. Department of Defense
– Identified and categorized operating system features
– Seven levels of security
• Compliance with Class C2 level security
– Features in Windows
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A secure logon facility
Discretionary access control
Auditing ability
Memory protection
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Security Basics (cont'd.)
• Multilayered security system
– Strives to prevent access by unauthorized users
• Password management: first security layer
• NTFS: second security layer
– File access security
• Distinguishes between owners and groups
• Users decide operation types person is allowed to
perform on a file
• Gives user auditing capabilities
– Automatically keeps track of who uses files and how
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Security Terminology
• Built-in security
– Necessary element for managers of Web servers and
networks
– Requires authentication mechanism allowing client to
prove identity to server
– Client supplies authorization information
– Server uses information to determine specific access
rights given to client
– Provides data integrity using various methods
• Windows uses Kerberos security
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Security Terminology (cont'd.)
• Kerberos Security
– Authentication, data integrity, data privacy, mutual
authentication
– Each domain has own Kerberos server
– Microsoft implemented standard Kerberos protocol
– Microsoft separated users of distributed security
services from their providers
• Allows support for many options without unusable
complexity
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Security Terminology (cont'd.)
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User Interface
• Start an application
– Double-click application icon
– Select it from Start menu
• Quit application
– Select Exit from File menu
– Click “x” in top-right corner of window
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User Interface (cont'd.)
• Start Menu
– Divides functions into logical groups
– Users access common functions
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All Programs
Documents, Pictures, Music, and Computer
Control Panel
Help and Support
Search
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User Interface (cont'd.)
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User Interface (cont'd.)
• Windows Task Manager
– Open
• Pressing and holding the CTRL, ALT, delete keys
– User view running applications and processes
• Set priorities of each
– User views information
• Performance, networking, users logged into system
• Windows Explorer (standard utility program)
– Contains director, file display tools, file-finding tool
– Series of pull-down menus
• File, Edit, View, Tools, Help, etc.
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User Interface (cont'd.)
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User Interface (cont'd.)
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User Interface (cont'd.)
• Networked systems
– Identify and access network resources
• Folders, printers, connections to other nodes
• Command interface
– Resembles MS-DOS
– Available from most Windows desktops
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Keyboard shortcuts: (CTRL+C for copy)
Built-in input methods and fonts for languages
Windows offers an on-screen keyboard
Resource monitor
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User Interface (cont'd.)
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User Interface (cont'd.)
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User Interface (cont'd.)
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User Interface (cont'd.)
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User Interface (cont'd.)
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Summary
• Current Windows operating systems
– Ease-of-use with technical power
– Operate network across several platforms
• Significant security controls
– Allowed inroads to organizations requiring consistent
protection
– Authentication models support new user interfaces
– Implementation of different security architectures
• Require aggressive patch management
– Target of viruses and worms
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