Understanding Operating Systems
Fifth Edition
Chapter 15
Windows Operating Systems
Learning Objectives
• The role of MS-DOS in early Windows releases
• The design goals for Windows operating systems
• The role of the Memory Manager and Virtual
Memory Manager
• The use of the Device, Processor, and Network
Managers in recent versions of Windows
• The challenges for Windows system security
• How the current Windows user interface functions
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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 (continued)
• 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 (Newer Technology)
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Operating Systems for Home and
Professional Users (continued)
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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
(continued)
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Operating Systems for Networks
(continued)
• 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
(continued)
• 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
• Large data warehouses
• Data-intensive business applications
• Supported up to 64 GB physical memory
• Windows Server 2003
– Same four packages plus Web edition
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Operating Systems for Networks
(continued)
• Server and Advanced Server editions
– Easy
• Form collaborative work groups across departments
• Add new workstations and components
– Improvements
• Network systems
• Adding new applications
• Maintaining system as a whole
– Web server software tools and support
• E-mail, conferencing, and collaboration
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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 (continued)
• 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 (continued)
• 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 (continued)
• 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 (continued)
• 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 (continued)
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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
(continued)
• 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
(continued)
• 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 (continued)
• 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 (continued)
• 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 (continued)
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Processor Management (continued)
• 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 (continued)
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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 (continued)
• 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 (continued)
• 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 (continued)
• 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 (continued)
• 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 (continued)
• 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 (continued)
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Device Management (continued)
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Device Management (continued)
• 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 (continued)
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Device Management (continued)
• 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 (continued)
• 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 (continued)
• 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 (continued)
• 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 (continued)
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File Management (continued)
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File Management (continued)
• 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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MS-NET
• 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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MS-NET (continued)
• 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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MS-NET (continued)
• 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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MS-NET (continued)
• 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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MS-NET (continued)
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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 (continued)
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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 (continued)
• 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 (continued)
• 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 (continued)
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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 (continued)
• 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 (continued)
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User Interface (continued)
• 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 (continued)
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User Interface (continued)
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User Interface (continued)
• 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 (continued)
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User Interface (continued)
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User Interface (continued)
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User Interface (continued)
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User Interface (continued)
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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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