Chapter 14
Windows Operating Systems
Understanding Operating Systems,
Fourth Edition
Objectives
You will be able to describe:
• The importance of MS-DOS in early Windows
releases
• The design goals for Windows operating systems
• The role of the Memory Manager, especially the
Virtual Memory Manager
• The use of the Device, Processor, and Network
Managers in recent versions of Windows
• The role of the NT file system in file management
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Objectives (continued)
You will be able to describe:
• The challenges for Windows system security today
• How the current Windows user interface functions
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Windows Development
Early Windows GUI Products ran “on top of” MS-DOS
Table 14.1: Windows Development
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Windows Development (continued)
• Windows for Workgroups:
– First Windows product to accommodate the needs of
network users
– Could easily share directories, disks, and printers
among several interconnected machines
– Allowed personal intercommunication through e-mail
and chat programs
– Intended for small or mid-sized groups of PCs for
small businesses or small departments of larger
organizations
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Operating Systems for Single Users
• Disadvantages of running Windows on top of
MS-DOS:
–
–
–
–
Little built-in security
Couldn’t perform multitasking
Had no interprocess communication capability
Written to work closely with the microcomputer’s
hardware
• Making it difficult to move OS to other platforms
• Microsoft developed and released a succession of
Windows OSs (not mere GUIs) to appeal to home
and office users
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Operating Systems for Single Users
(continued)
Table 14.2: Evolution of key Microsoft Windows operating
systems for home and professional use
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Operating Systems for Networks
• Development of Windows NT (more powerful
networking products):
– Windows NT never relied on MS-DOS for support
– Primary market requirements include:
•
•
•
•
Portability
Multiprocessing capabilities
Distributed computing support
Compliance with government procurement
requirements
• Government security certification
– The finished product was introduced in 1993
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Operating Systems for Networks
(continued)
Table 14.3: Evolution of key Microsoft Windows networking
operating systems. All have evolved from Windows NT
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Operating Systems for Networks
(continued)
• Microsoft offered Windows NT in several versions:
– Windows NT Workstation for individuals needing a
desktop operating system
– Windows NT Server for small to medium-sized
offices, Web servers, and off-site locations
– Windows NT Server Enterprise Edition for larger and
more complex networks
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Operating Systems for Networks
(continued)
• In 1999, Windows NT name was changed to
Windows 2000 and was available in four packages:
–
–
–
–
Windows 2000 Professional
Windows 2000 Server
Windows 2000 Advanced Server
Windows 2000 Datacenter Server
• Designed for large data warehouses and other dataintensive business applications
• Supported up to 64 GB of physical memory
• Windows Server 2003 was also released with
these same four packages plus a Web edition
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Design Goals
• To accommodate various needs of its users and to
optimize resources, the Windows design team
identified five design goals:
–
–
–
–
–
Extensibility
Portability
Reliability
Compatibility
Performance
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Extensibility
• Allows the system to be easily enhanced
• To ensure the integrity of code, designers
separated operating system functions into:
– Privileged executive process (kernel mode)
• Refers to a processor’s mode of operation in which all
machine instructions are allowed
• System memory is accessible
– Nonprivileged processes “protected subsystems”
(user mode):
• Certain instructions are not allowed
• System memory isn’t accessible
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Extensibility (continued)
• Windows designers also included four more
features to ensure extensibility:
– Modular structure so new components can be
added to the executive process
– Objects, a group of abstract data types manipulated
by a special set of services
• Allow system resources to be managed uniformly
– Drivers for new file systems, devices, and networks
that can be added to the system at any time
– Remote procedure call
• Allows an application to call remote services
regardless of their location on the network
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Portability
• Ability to operate on different machines that are
based on different processors or configurations
with a minimum amount of recoding
• To achieve this goal, Windows development
followed certain guidelines:
– Written in a standardized, high-level language
available in all machines
– System accommodated hardware to which it was
expected to be ported
– Minimized code that interacted directly with the
hardware — to reduce incompatibility errors
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Portability (continued)
(continued)
– Isolation of all hardware-dependent code into
modules - that could be easily modified whenever
the operating system was ported
• Windows NT and successors have the following
features:
– Modular code
– Much of Windows is written in C
– Contains a hardware abstraction layer (HAL)
• A dynamic-link library that provides isolation from
hardware dependencies furnished by different vendors
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Reliability
• Refers to the robustness of a system and its ability
to protect itself and its users from accidental or
deliberate damage by user programs
• Following features strengthen the system:
– Structured exception handling
– Modular design
– NTFS File System (NT File System) which can
recover from all types of errors
– U.S. government-certifiable security architecture
– Virtual memory strategy
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Compatibility
• Refers to an operating system’s ability to execute
programs written for other operating systems or for
earlier versions of the same system
– Use of protected subsystems
• Provides execution of applications that are different
from its primary programming interface
– Provides source-level compatibility with POSIX
applications
– Recent versions of Windows support already-existing
file systems, e.g., MS-DOS FAT, CDFS, and NTFS
– Built-in verification of important hardware and
software
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Performance
• Several features that help Windows achieve good
performance levels include:
– Testing and optimization of system calls, page faults,
and other crucial processes
– Incorporation of local procedure call (LPC) — to
guarantee fast communication among the protected
subsystems
– Speed of frequently used system services is
maximized
– Critical elements of Windows’ networking software
are built into privileged portion of operating system
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Memory Management
• Every operating system uses its own view of
physical memory and makes its application
programs access memory in specified ways
• When physical memory becomes full, the Virtual
Memory Manager pages some of the memory
contents to disk, freeing physical memory for other
processes
• Challenge for all Windows OSs: To run
application programs written for Windows, MSDOS, or POSIX without programs crashing into
each other’s memory
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Memory Management (continued)
Memory layout in recent versions of Windows:
• Operating system resides in high virtual memory
and the user’s code and data reside in low virtual
memory
• User process can’t read or write to system memory
directly
• All user-accessible memory can be paged to disk,
as can the segment of system memory labeled
paged pool
• Segment of system memory labeled nonpaged
pool is never paged to disk
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Memory Management (continued)
Figure 14.1: Layout of Windows memory
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User-Mode Features
• VM Manager allows user-mode subsystems to
share memory efficiently
• Provides services that a process can use to
manage its virtual memory in the following ways:
–
–
–
–
–
–
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
• Virtual Memory Manager relies on:
– Address space management
– Paging techniques
• Address Space Management:
– Upper half of the virtual address space is accessible
only to kernel-mode processes
– Code in the lower part of this section, kernel code
and data, is never paged out of memory
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Paging
• Pager: Part of VM manager that transfers pages
between page frames in memory and disk storage
and is a complex combination of:
– Software policies
• Determine when to bring a page into memory and
where to put it
– Hardware mechanisms
• Include the exact manner in which the VM Manager
translates virtual addresses into physical addresses
• Pager is not portable
• Windows keeps this code small and well isolated
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Paging (continued)
• Paging policies dictate how and when paging is
done and are composed of:
– Fetch policy
• Determines when the pager copies a page from disk
to memory
– Placement policy
• Determines where the virtual page is loaded in
memory
– Replacement policy
• Determines which virtual page must be removed from
memory to make room for a new page
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Processor Management
• Windows is a preemptive-multitasking,
multithreaded operating system
• Process in Windows NT-derived OS requires at
least one thread of execution. By default, a process
contains one thread, which is composed of:
– A unique identifier
– Contents of a volatile set of registers indicating
processor’s state
– Two stacks used during the thread’s execution
– Private storage area used by subsystems and
dynamic-link libraries
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Processor Management (continued)
Threads:
• Thread components are called the thread’s context
• Actual data forming this context varies from one
processor to another
• Kernel schedules threads for execution on a
processor
• The thread is what actually executes the code
• The overhead incurred by a thread is minimal
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Processor Management (continued)
Figure 14.2: Unitasking in Windows
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Processor Management (continued)
Multithreading:
• For systems with multiple processors, a process
can have as many threads as there are CPUs
available
• All threads belonging to one process share its
global variables, heap, and environment strings
• Versions of Windows since NT include some
synchronization mechanisms to avoid problems
with multiple threads
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Processor Management (continued)
Figure 14.3: Multitasking using multithreading
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Device Management
• The I/O system in Windows NT and its networking
descendents was designed to provide following:
– Multiple installable file systems including FAT, CDFS,
and NTFS
– Services to make device-driver development as easy
as possible yet workable on multiprocessor systems
– Ability for system administrators to add drivers to the
system or remove them from the system dynamically
– Fast I/O processing while allowing drivers to be
written in high-level language
– Mapped file I/O capabilities for image activation, file
caching, and application use
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Device Management (continued)
• The I/O system is packet driven i.e., every I/O
request is represented by an I/O request packet
(IRP)
– An IRP is a data structure that controls how the I/O
operation is processed at each step
• I/O Manager
– Creates an IRP that represents each I/O operation
– Passes the IRP to the appropriate driver
– Disposes of the packet when the operation is
complete
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Device Management (continued)
Table 14.4: Example showing how a device object is
created from an instruction to read a file
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Device Management (continued)
• Tasks of I/O Manager:
–
–
–
–
Supplies code, common to different drivers
Manages buffers for I/O requests
Provides time-out support for drivers
Records which installable file systems are loaded
into the operating system
– Provides flexible I/O facilities
• Allow subsystems such as POSIX to implement their
respective I/O application programming interfaces
– Allows device drivers and file systems to be loaded
dynamically based on the needs of the user
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Device Management (continued)
• Windows provides a device-independent model for
I/O services
– This model takes advantage of a concept called a
“multilayered device driver”
• Each device driver is made up of a standard set of
routines including the following:
– 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 must determine from the file object’s
name which driver should be called to process the
request of accessing a file. It uses:
– Driver object:
• Represents an individual driver in the system
• I/O Manager creates it when a driver is loaded into the
system
• A driver object may have multiple device objects
connected to it
– Device object:
• Represents a physical, logical, or virtual device on the
system and describes its characteristics
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Device Management (continued)
Figure 14.4: The driver object from Table 14.4 is
connected to several device objects. The last device
object points back to the driver object
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Device Management (continued)
• The list of device objects represents the physical,
logical, and virtual devices that are controlled by
the driver
• Advantages to representing devices and
drivers with different objects:
– Provides portability: Frees the I/O manager from
having to know details about individual drivers
• It just follows a pointer to locate a driver
– Allows new drivers to be easily loaded
– Easier to assign drivers to control additional or
different devices if system configuration changes
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Device Management (continued)
Figure 14.5: Interaction
of I/O Manager with a
layered device driver to
write data to a file on a
hard disk
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Device Management (continued)
• The I/O Manager knows nothing about the file
system
• Overhead involved when the I/O Manager passes
requests for information back and forth
– Uses single-layer device driver approach for simple
devices, e.g., serial and parallel printer ports
– Uses multilayered approach for more complicated
devices, e.g., hard drives
• Almost all low-level I/O operations are
asynchronous
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File Management
• Current versions of Windows are designed to be
independent of the file system on which they
operate
• Windows supports multiple file systems for hard
disks including:
– MS-DOS’s FAT file system
– 32-bit FAT file system
– NTFS
• NTFS extends the capabilities of the FAT and
FAT32 file systems
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File Management (continued)
• NTFS extends the capabilities of the FAT and
FAT32 file systems by adding:
– File system recovery
– Ability to handle large storage media, on the order of
approximately 17 billion gigabytes in size
– Security features, including execute-only files
– Unicode filenames
– Support for the POSIX operating system
environment
– Features for future extensibility
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File Management (continued)
• Primary file handling concept in current versions of
Windows is the virtual file
• Programs perform I/O on virtual files, manipulating
them by using file handles
– An executive file object that represents all sources
and destinations of I/O
• Processes call native file object services such as
those to read from or write to a file
• I/O Manager directs these virtual file requests to
real files, file directories, physical devices
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File Management (continued)
• File objects:
–
–
–
–
Have hierarchical names,
Protected by object-based security
Support synchronization
Handled by object services
• When opening a file, a process supplies the file’s
name and the type of access required
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File Management (continued)
File objects:
• Help bridge the gap
– Between the characteristics of physical devices and
directory structures, file system structures, and data
formats
• Provide a memory-based representation of
shareable physical resources
• Are created with a new set of handle-specific
attributes each time a process opens a handle
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File Management (continued)
Figure 14.6: Illustration of a
file object, its attributes, and
the services that operate on
them
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File Management (continued)
Table 14.5: Description of the attributes shown in Figure 14.6
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File Management (continued)
• Mapped file I/O is an important feature of the I/O
system
– Achieved through the cooperation of the I/O system
and the VM Manager
• Memory-mapped files exploit virtual memory
capabilities
• Cache manager uses mapped I/O to manage its
memory-based cache
• NTFS supports long filenames that can include
spaces and special characters
– Automatically shortens filenames when required
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Network Management
• Networking is an integral part of the Windows NTbased operating systems and provides services
such as:
– User accounts, resource security
– Mechanisms used to implement communication
between computers, such as with named pipes and
mailslots
• Named pipes provide a high-level interface for
passing data between two processes regardless of
their locations
• Mailslots provide one-to-many and many-to-one
communication mechanisms
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MS-NET
• Microsoft Networks(MS-NET) was released in 1984
and became the model for the NT Network
Manager
• Three MS-NET components:
– Redirector
– Server message block (SMB) protocol
– Network server
• MS-NET components were extensively refurbished
and incorporated into Windows NT and later
versions
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MS-NET (continued)
• Redirector:
– Coded in the C programming language
– Implemented as a loadable file system driver
– Not dependent on the system’s hardware
architecture
– Function: To direct an I/O request from a user or
application to the remote server that has the
appropriate file or resource
• A network can incorporate multiple redirectors
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MS-NET (continued)
SMB Protocol:
• A high-level specification for formatting messages
to be sent across the network
• Correlates to the application layer (layer 7) and the
presentation layer (layer 6) of the OSI model
• An API called NetBIOS interface is used to pass
I/O requests structured in the SMB format to a
remote computer
• Both SMB protocols and NetBIOS API were
adopted in several networking products before
appearing in Windows
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MS-NET (continued)
Windows Server operating systems:
• Written in C for complete compatibility with existing
MS-NET and LAN manager SMB protocols
• Implemented as loadable file system drivers
• Have no dependency on the hardware architecture
on which the operating system is running
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MS-NET (continued)
Figure 14.7: Implementation of the seven layers of the OSI
reference model in the Windows Network Manager
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Directory Services
• Active Directory: Database that stores all types of
information so it can be a general-purpose
directory service for a 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
• A 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)
Figure 14.8: Active Directory clients use standard DNS
and LDAP protocols to locate objects on the network
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Security Management
• Windows network operating systems provide an
object-based security model
– A security object can represent any resource in the
system: a file, device, process, program, or user
– Allows administrators to give precise security access
to specific objects in the system while allowing them
to monitor and record how objects are used
• Biggest concern in Windows OS: Need for
aggressive patch management
– To combat many viruses and worms that target these
systems
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Security Basics
• U.S. Department of Defense has identified and
categorized OS features into seven levels of
security
• To comply with the Class C2 level of security,
Windows 2000 and above include the following
features:
–
–
–
–
A secure logon facility
Discretionary access control
Auditing ability
Memory protection
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Security Basics (continued)
• Windows strives to prevent access by unauthorized
users by supporting a multilayered security system
– Password management is the first layer of security
– In NTFS, users encounter a second layer of security
that deals directly with file access security
– Windows makes distinctions between owners and
groups
– Users can decide what type of operations a person
is allowed to perform on a file
– Gives the user auditing capabilities that
automatically keep track of who uses files and how
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Security Terminology
• Built-in security for recent Windows network OS
is a necessary element for managers of Web
servers and networks
– Requires an authentication mechanism that allows a
client to prove its identity to a server
– Client needs to supply authorization information
• Server uses it to determine which specific access
rights have been given to client
– Needs to provide data integrity using a variety of
methods
• Windows provide this with Kerberos security
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Security Terminology (continued)
Kerberos Security:
• Provides authentication, data integrity, data privacy,
and mutual authentication
• Each domain has its own Kerberos server
• Microsoft has implemented the standard Kerberos
protocol
• Microsoft has separated the users of distributed
security services from their providers
– Allows support for many options without creating
unusable complexity
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Security Terminology (continued)
Figure 14.9: Requests from
an application flow through a
series of security providers,
as do the responses from the
network back to application
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User Interface
• Desktop contains the icons for the tools and
applications one can use to get work done
– Users can use mouse, light pen, or stylus to move
around the desktop
• To start an application, users double-click an
application icon or select it from the Start menu
• To quit an application, they can select Exit from the
File menu or click the “x” in the top-right corner of
the window
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User Interface (continued)
• Start Menu divides functions into logical groups
and from here users access common functions
including the following:
– All Programs
– My Documents, My Pictures, My Music, My
Computer
– Control Panel, Help and Support
– Search, Run, Log Off, Turn Off Computer
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User Interface (continued)
Figure 14.10: A typical Windows Start Menu
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User Interface (continued)
• The Windows Task Manager:
– Opened by pressing and holding the Ctrl, Alt, and
Delete keys
– Allows user to view running applications and
processes, and set the priorities of each
– Allows user to view information about performance,
networking, and other users logged into system
• Windows Explorer: Contains directory and file
display tools and a file-finding tool
– Features a series of pull-down menus: File, Edit,
View, Favorites, Tools, Help, etc.
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User Interface (continued)
• My Network Places: helps users identify and
access network resources such as folders, printers,
and connections to other nodes
• Command interface that resembles MS-DOS is
available from most Windows desktops
• Keyboard shortcuts: e.g., Ctrl+C for copy
• Built-in input methods and fonts for many
languages.
– e.g., Administrator can select one or several
languages during installation
• Windows also offers an on-screen keyboard
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Summary
• Current Windows operating systems incorporate
ease-of-use with the technical power to operate a
network across several existing platforms
• Windows systems are designed to evolve
modularly and consistently over time
• Portability feature eases the difficulty of migrating
OS to new hardware platforms
• Security controls in Windows have helped OS gain
inroads with organizations requiring consistent
protection for their data and applications
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Summary (continued)
• Windows’ authentication models support new user
interfaces from bank teller machines to fingerprint
or retinal scanners
• Allow the implementation of different security
architectures, further extending the reach of
Windows into the market
• Require aggressive patch management to combat
viruses and worms
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