Chapter 11 Operating Systems

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Chapter 11Operating Systems
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Outline

• Functional overview of an operating system
• Process management
• Resource allocation
• CPU allocation
• Memory allocation
• Interprocess communication

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Operating System Overview

• Operating System Management Functions
• Operating System Layers

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Operating System Overview

• The operating system oversees all hardware
  resources and allocates them to user and
  applications as needed.
• The operating system performs many low-level
  tasks on behalf of users and application programs.

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Operating System Overview

• Operating System Management Functions
• The operating system manages
• Hardware resources
• Users and their programs

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Operating System Overview

• Operating System Layers
• Command Layer
• Service Layer
• Kernel

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Operating System Layers
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Operating System Layers

• Operating System Layers
• Command Layer the users interface to the
  operating system.
• Service Layer contains a set of functions
  called by application programs and the command
  layer.
• Kernel manages resources and directly interacts
  with computer hardware.

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Outline

• Functional overview of an operating system
• Process management
• Resource allocation
• CPU allocation
• Memory allocation
• Interprocess communication

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Process Management

• Process Control Data Structures
• A process is a unit of executing software that is
  managed independently by the operating system.
• A process can request and receive hardware
  resources and operating system services.

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Process Management

• Process Control Data Structures
• Process Control Block (PCB) keeps track of each
  process by creating and updating a data
  structure.
• The PCB is created when the process is created,
  updated when the process changes and deleted when
  the process terminates.

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Process Management

• Data included in a PCB
• A unique process identification number
• The current state of the process
• Events for which the process is waiting
• Resources allocated exclusively to the process
• Machine resources consumed
• Process ownership and/or access privileges
• Scheduling priority

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Process Management

• Threads
• A portion of a process that can be scheduled and
  executed independently.
• Process light
• Thread can execute concurrently on a single
  processor or simultaneously on multiple
  processors.

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Outline

• Functional overview of an operating system
• Process management
• Resource allocation
• CPU allocation
• Memory allocation
• Interprocess communication

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Resource Allocation

• Single Process Resource Allocation
• Multiple Process Resource Allocation
• Resource Allocation Processes
• Real and Virtual Resources

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Resource Allocation

• Single Process Resource Allocation
• Involves only two executing programs
  application and operating system.
• When an application program begins executing, the
  operating system grants it control of all unused
  resources.

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Resource Allocation

• Single Process Resource Allocation
• Most service calls are actually indirect requests
  for system resources.
• MS-DOS is a single-tasking operating system.

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Resource Allocation

• Multiple Process Resource Allocation
• Multitasking operating systems are the norm for
  general-purpose computers.
• Multitasking operating systems must be able to
  handle multiple programs and users.

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Resource Allocation

• Multiple Process Resource Allocation
• A multitasking operating system manages hardware
  resources to achieve the following
• Meet the resource needs of processes
• Prevent processes from interfering with one
  another
• Efficiently use hardware and other resources

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Resource Allocation

• Resource Allocation Processes
• Keeps detailed records of available resources.
• Knows which resource are used to satisfy which
  requests.
• Schedules resources based on specific allocation
  policies to meet present and anticipated demands.
• Updates records to reflect resources commitment
  and release by processes and users.

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Resource Allocation

• Real and Virtual Resources
• Real resource a computer systems physical
  devices and associated system software.
• Virtual resource the resources that are
  apparent to a process or user.

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Real and Virtual Resources

• Providing virtual resources that meet or exceed
  resources is accomplished by
• Rapidly shifting resources unused by one process
  to other processes that need them.
• Substituting one type of resource for another
  when possible and necessary.

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CPU Allocation

• Thread States
• Interrupt Processing
• Scheduling

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CPU Allocation

• A thread controls the CPU for no more than a few
  milliseconds before it relinquishes control and
  the operating system gives another thread a turn.
• CPU sharing is called concurrent execution or
  interleaved execution.

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CPU Allocation
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CPU Allocation

• Thread States
• Ready
• Running
• Blocked

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CPU Allocation
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CPU Allocation

• Ready State a thread is waiting for access to a
  CPU.
• Running State the thread has control of the
  CPU.
• The thread or its parent process terminates
  normally
• An interrupt occurs
• Block State the thread is suspended while an
  interrupt is being processed.

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CPU Allocation

• Interrupt Processing
• A blocked thread is waiting for an event to
  occur.
• If the event is the correction of an error and it
  can be corrected, the thread remains in the
  blocked state until the error condition is
  resolved otherwise, the thread is halted.

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Scheduling

• Preemptive Scheduling
• Priority-based Scheduling
• Real-time Scheduling

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Scheduling

• Preemptive Scheduling
• A thread can be removed involuntarily from the
  running state.
• A running process controls the CPU by controlling
  the content of the instruction pointer.
• CPU control is lost whenever an interrupt is
  received.

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Scheduling
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Scheduling
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Scheduling

• Priority-Based Scheduling Methods
• First come First served
• Explicit priority
• Shortest time remaining

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Scheduling

• Priority-Based First come first served
• The scheduler always dispatches the ready thread
  that has been waiting the longest.

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Scheduling

• Priority-Based Explicit priority
• Uses a set of priority levels and assigns a level
  to each process or thread.
• The scheduling method can use priority levels in
  two ways
• Always dispatch the highest priority ready thread
• Assign larger time slices to high priority
  threads

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Scheduling

• Priority-Based Shortest time remaining
• Chooses the next process to be dispatched based
  on the expected amount of CPU time needed to
  complete the process.

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Scheduling

• Real-Time Scheduling
• Guarantees a minimum amount of CPU time to a
  thread if the thread makes an explicit request
  when it is created.
• Used when a thread must have enough resources to
  complete its function within a specified time.

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Technology Focus

• Windows 2000 Scheduling

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Technology Focus
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Memory Allocation

• Single-Tasking Memory Allocation
• Multitasking Memory Allocation
• Memory Fragmentation
• Noncontiguous Memory Allocation
• Virtual Memory Management
• Memory Protection
• Memory Management Hardware

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Memory Allocation

• Single-Tasking Memory Allocation Contiguous
  Memory Allocation
• The bulk of the operating system occupies lower
  memory addresses.
• The application program is loaded above the
  operating system.
• The remaining space is available for user
  programs and data.

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Memory Allocation
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Memory Allocation

• Single-Tasking Memory Allocation Noncontiguous
  Memory Allocation
• To conserve physical memory, some operating
  system components are loaded into memory only
  when needed.
• When loaded, they usually are placed in upper
  memory.

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Memory Allocation
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Memory Allocation

• Multitasking Memory Allocation
• The goals of multitasking memory allocation are
• Allow as many active processes as possible.
• Respond quickly to changing memory demands of
  processes.
• Prevent unauthorized changes to a processs
  memory region(s).
• Implement memory allocation and addressing as
  efficiently as possible.

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Memory Allocation
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Memory Allocation
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Memory Allocation
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Memory Allocation

• Memory Fragmentation
• As processes are created, executed, and
  terminated, memory allocation changes
  accordingly.
• Memory partition allocation and deallocation
  leads to an increasing number of small free
  partitions separated by allocated partitions.

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Memory Allocation
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Memory Allocation
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Memory Allocation

• Noncontiguous Memory Allocation
• Uses small fixed-size partitions, usually no
  larger than 64K.
• A process can be loaded into more than one
  partition.

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Memory Allocation
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Memory Allocation

• Virtual Memory Management
• Divides a program into partitions called pages.
• Memory is divided into pages called a page frame.
• During program execution, one or more program
  pages are stored in a page frame, the remaining
  are stored on a secondary storage device.

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Memory Allocation
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Memory Allocation

• Memory Protection
• Refers to the protection of memory allocated to
  one program from unauthorized access by another
  program.
• The operating system checks each write to a
  memory location to ensure that the address being
  written is allocated to the program performing
  the write operation.

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Memory Allocation

• Memory Management Hardware
• Modern CPUs and computer systems incorporate
  advanced memory allocation and address resolution
  functions in hardware.

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Technology Focus
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Technology Focus
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Outline

• Functional overview of an operating system
• Process management
• Resource allocation
• CPU allocation
• Memory allocation
• Interprocess communication

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Interprocess Communication

• Interprocess Signals
• Interprocess Data Communication

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Interprocess Communication

• Interprocess Signals
• A signal is a message used to synchronize the
  actions of two processes or threads.
• Signals can be sent between threads of the same
  process, between independent processes, or
  between the operating system and a process or
  thread.

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Interprocess Communication
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Interprocess Communication
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Interprocess Communication
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Interprocess Communication

• Interprocess Data Communication
• Operating systems provide a mechanism called a
  pipe so there can be communication via shared
  memory between independent processes.

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Interprocess Communication
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Interprocess Communication
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Summary

• An operating system is the most complex component
  of system software.
• The operating system allocates hardware resources
  to individual user processes on demand.
• The operating system stores information about
  each process in a PCB.

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Summary

• Application software is simper to develop if
  programs are unaware of resource allocation
  functions.
• An active thread is always in one of three states
  ready, running, or blocked.

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Summary

• Memory is divided into fixed-size partitions and
  processes are allocated one or more memory
  partitions to store instructions and data.
• Modern operating systems implement a form of
  memory allocation and management called virtual
  memory management.

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Summary

• Processes and threads often need to synchronize
  their actions or transfer data among themselves
  using signals and pipes.