Chapter 22: Windows XP

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Chapter 22 Windows XP
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Module 22 Windows XP

• History
• Design Principles
• System Components
• Environmental Subsystems
• File system
• Networking
• Programmer Interface

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Objectives

• To explore the principles upon which Windows XP
  is designed and the specific components involved
  in the system
• To understand how Windows XP can run programs
  designed for other operating systems
• To provide a detailed explanation of the Windows
  XP file system
• To illustrate the networking protocols supported
  in Windows XP
• To cover the interface available to system and
  application programmers

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Windows XP

• 32-bit preemptive multitasking operating system
  for Intel microprocessors
• Windows XP 64-bit Edition (July 2005)
• Key goals for the system
• portability
• security
• POSIX compliance
• multiprocessor support
• extensibility
• international support
• compatibility with MS-DOS and MS-Windows
  applications.
• Uses a micro-kernel architecture
• Available in four versions, Professional, Server,
  Advanced Server, National Server

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History Windows 1.0
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History Windows 2.0
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History Windows 3.0
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History OS/2
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History OS/2

• Microsoft and IBM had co-operatively been
  developing OS/2 as a successor to DOS.
• OS/2 1.0, released in 1987, supported swapping
  and multitasking and allowed running of DOS
  executables.
• A GUI, called the Presentation Manager (PM), was
  not available with OS/2 until version 1.1,
  released in 1988.
• By the early 1990s, conflicts developed in the
  Microsoft/IBM relationship. In an attempt to
  resolve this tension, IBM and Microsoft agreed
  that IBM would develop OS/2 2.0, to replace OS/2
  1.3 and Windows 3.0, while Microsoft would
  develop a new operating system, OS/2 3.0, to
  later succeed OS/2 2.0.
• This agreement soon however fell apart, and the
  Microsoft/IBM relationship was terminated. IBM
  continued to develop OS/2, while Microsoft
  changed the name of its (as yet unreleased) OS/2
  3.0 to Windows NT.

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History Windows 3.1 and NT
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History Windows NT 4.0
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History Windows 98
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History Windows 2000
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History Windows Me
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History Windows Me
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History

• In 1988, Microsoft decided to develop a new
  technology (NT) portable operating system that
  supported both the OS/2 and POSIX APIs
• Originally, NT was supposed to use the OS/2 API
  as its native environment but during development
  NT was changed to use the Win32 API, reflecting
  the popularity of Windows 3.0

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Design Principles

• Extensibility layered architecture
• Executive, which runs in protected mode, provides
  the basic system services
• On top of the executive, several server
  subsystems operate in user mode
• Modular structure allows additional environmental
  subsystems to be added without affecting the
  executive
• Portability XP can be moved from on hardware
  architecture to another with relatively few
  changes
• Written in C and C
• Processor-dependent code is isolated in a dynamic
  link library (DLL) called the hardware
  abstraction layer (HAL)

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Design Principles (Cont.)

• Reliability XP uses hardware protection for
  virtual memory, and software protection
  mechanisms for operating system resources
• Compatibility applications that follow the IEEE
  1003.1 (POSIX) standard can be complied to run on
  XP without changing the source code
• Performance XP subsystems can communicate with
  one another via high-performance message passing
• Preemption of low priority threads enables the
  system to respond quickly to external events
• Designed for symmetrical multiprocessing
• International support supports different
  locales via the national language support (NLS)
  API

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XP Architecture

• Layered system of modules
• Protected mode HAL, kernel, executive
• User mode collection of subsystems
• Environmental subsystems emulate different
  operating systems
• Protection subsystems provide security functions

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Depiction of XP Architecture
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Kernel-Mode Components

• Executive
• Contains base operating system services
• Memory management
• Process and thread management
• Security
• I/O
• Interprocess communication
• Kernel
• Consists of the most used components

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Kernel-Mode Components

• Hardware abstraction layer (HAL)
• Isolates the operating system from
  platform-specific hardware differences
• Device drivers
• Translate user I/O function calls into specific
  hardware device I/O requests
• Windowing and graphics systems
• Implements the graphical user interface (GUI)

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Windows Executive

• I/O manager
• Cache manager
• Object manager
• Plug and play manager
• Power manager
• Security reference monitor
• Virtual memory manager
• Process/thread manager
• Configuration manager
• Local procedure call (LPC) facility

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User-Mode Processes

• Special system support processes
• Eg. logon process and the session manager
• Service processes
• Eg. Event logger
• Environment subsystems
• Win32, POSIX OS/2
• User applications
• Win32, Win16 MS-DOS
• POSIX
• OS/2

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Client/Server Model

• Simplifies the Executive
• Possible to construct a variety of APIs
• Improves reliability
• Each service runs on a separate process with its
  own partition of memory
• Clients cannot not directly access hardware
• Provides a uniform means for applications to
  communicate via LPC
• Provides base for distributed computing

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Threads and SMP

• Operating system routines can run on any
  available processor
• Different routines can execute simultaneously on
  different processors
• Multiple threads of execution within a single
  process may execute on different processors
  simultaneously
• Server processes may use multiple threads
• Share data and resources between process

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Windows Objects

• Encapsulation
• Object consists of one or more data items and one
  or more procedures
• Object class or instance
• Create specified instances of an object
• Inheritance
• Support to some extent in the Executive
• Polymorphism

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Windows Processes

• Implemented as objects
• An executable process may contain one or more
  threads
• Both processes and thread objects have built-in
  synchronization capabilities

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Windows Process Object
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Windows Thread Object
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Windows 2000/XP Thread States
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User-Level Threads

• A fiber is user-mode code that gets scheduled
  according to a user-defined scheduling algorithm
• Only one fiber at a time is permitted to execute,
  even on multiprocessor hardware
• XP includes fibers to facilitate the porting of
  legacy UNIX applications that are written for a
  fiber execution model

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Windows Synchronization

• To synchronize the concurrent access to shared
  objects by threads, the kernel provides
  synchronization objects
• Semaphores
• Mutexes
• In addition, threads can synchronize by using
• WaitForSingleObject
• WaitForMultipleObjects
• Another method of synchronization in the Win32
  API is the critical section

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Inter-process Comm.

• Win32 applications can have interprocess
  communication by sharing kernel objects
• An alternate means of interprocess communications
  is message passing, which is particularly popular
  for Windows GUI applications
• One thread sends (synchronous) or posts
  (asynchronous) a message to another thread or to
  a window
• A thread can also send data with the message
• Every Win32 thread has its own input queue from
  which the thread receives messages

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Windows Memory Management

• A heap in the Win32 environment is a region of
  reserved address space
• A Win 32 process is created with a 1 MB default
  heap
• Access is synchronized to protect the heaps
  space allocation data structures from damage by
  concurrent updates by multiple threads
• Functions that rely on global or static data
  typically fail to work properly in a
  multithreaded environment
• Thread-local storage mechanism allocates global
  storage on a per-thread basis
• The mechanism provides both dynamic and static
  methods of creating thread-local storage

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Virtual Address Space
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Executive - Virtual Memory Manager

• Assumes that the underlying hardware supports
• Virtual to physical mapping
• A paging mechanism
• Transparent cache coherence on multiprocessor
  systems
• Many pages map to the same frame
• Uses a page-based management scheme with a page
  size of 4 KB
• Uses a two step process to allocate memory
• Reserve a portion of the process address space
• Commit the allocation by assigning space in the
  paging file or physical memory
• Processes has a quota on commited memory space

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Virtual-Memory Layout
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Virtual Memory Manager (Cont.)

• Each process in XP has
• A page directory with 1024 page directory entries
  (PDEs)
• Each PDE points to a page table
• A page table contains 1024 page table entries
  (PTEs)
• Each PTE points to a 4 KB page frame in physical
  memory
• A page can be in one of seven states
• Valid used by a process
• Free free to use
• Zeroed free to use and zeroed
• Modified needs to be written to disk
• Standby mirrors content on disk
• Bad hardware error
• In transition on its way from disk

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Virtual-to-Physical Address Translation

• 10 bits for page directory entry
• 10 bits for page table entry
• 12 bits for byte offset in page

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Page File Page-Table Entry

• 5 bits for page protection
• 20 bits for page frame address
• 4 bits to select a paging file
• 3 bits that describe the page state.

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Windows Scheduling

• Priority-driven preemptive scheduler
• Threads are the unit of execution scheduled by
  the kernels dispatcher
• Priorities organized into two bands or classes
• Real time
• Contains threads with priorities ranging from 16
  to 31
• Variable
• Contains threads having priorities from 0 to 15

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Windows Scheduling

• Characteristics of XPs priority strategy
• Tends to give very good response times to
  interactive threads that are using the mouse and
  windows
• Enables I/O-bound threads to keep the I/O devices
  busy
• Complete-bound threads soak up the spare CPU
  cycles in the background

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Windows I/O

• Basic I/O modules
• Cache manager
• File system drivers
• Network drivers
• Hardware device drivers

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I/O Manager

• Keeps track of which installable file systems are
  loaded
• Manages buffers for I/O requests
• Works with VM Manager to provide memory-mapped
  file I/O
• Controls the XP cache manager
• handles caching for the entire I/O system
• Supports both synchronous and asynchronous
  operations,
• provides time outs for drivers

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File I/O
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Windows File System

• Key features of NTFS
• Recoverability
• Security
• Large disks and large files
• Multiple data streams
• Eg. to handle macintosh files
• General indexing facility
• Files can be indexed by different attributes

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NTFS Volume and File Structure

• Sector
• The smallest physical storage unit on the disk
• Cluster
• One or more contiguous sectors
• Is used as the underlying unit of disk allocation
• Volume
• The fundamental structure of NTFS
• Logical partition
• Part of a disk
• Whole disk
• Span several disks
• All metadata is stored in a regular file

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NTFS Internal Layout

• Uses logical cluster numbers (LCNs) as disk
  addresses
• A file is a structured object consisting of
  attributes
• Not a simple byte stream, as in MS-DOS or UNIX
• Every file is described by one or more records in
  the MFT
• A special file called the Master File Table
• Each file on a volume has a unique ID called a
  file reference.
• 48-bit file number
• 16-bit sequence number
• Can be used to perform internal consistency
  checks
• The name space is organized by a hierarchy of
  directories
• The index root contains the top level of the B
  tree

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File System Security

• Security of an NTFS volume is derived from the XP
  object model
• Each file object has a security descriptor
  attribute stored in this MFT record
• This attribute contains
• The access token of the owner of the file
• An access control list
• States the access privileges granted to users
  that has access to the file

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File System Compression

• To compress a file, NTFS divides the files data
  into compression units, which are blocks of 16
  contiguous clusters
• For sparse files, NTFS uses another technique to
  save space
• Clusters that contain all zeros are not actually
  allocated or stored on disk
• Instead, gaps are left in the sequence of virtual
  cluster numbers stored in the MFT entry for the
  file
• When reading a file, if a gap in the virtual
  cluster numbers is found, NTFS just zero-fills
  that portion of the callers buffer

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End of Chapter 22