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Operating Systems

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Command Layer (shell) the user's interface to the operating system ... Process Control Block (PCB) keeps track of each process by creating and ... – PowerPoint PPT presentation

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Title: Operating Systems


1
Operating Systems
  • Chapter 11

2
Chapter Topics
3
Operating System Overview
  • Operating System Management Functions
  • Oversees all hardware resources and allocates
    them to user and applications as needed
  • Performs many low-level tasks on behalf of users
    and application programs

4
Operating System Overview
5
Operating System Overview
  • Operating System Layers
  • Command Layer (shell) 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

6
Operating System Overview
7
Operating System Overview
8
Resource Allocation
  • Resource Allocation Process
  • Keeps detailed records of available resources
  • Knows which resources 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

9
Resource Allocation
  • Single Process Resource Allocation (application
    program and operating system)
  • When an application program begins executing, the
    operating system grants it control of all unused
    resources
  • Most service calls are actually indirect requests
    for system resources

10
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
  • 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

11
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

12
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

13
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.

14
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

15
CPU Allocation
  • Concurrent Execution (Interleaved Execution)
  • A thread is a portion of a process that can be
    scheduled and executed independently.
  • It controls the CPU for no more than a few
    milliseconds before it relinquishes control and
    the operating system gives another thread a turn

16
CPU Allocation
17
CPU Allocation
  • Ready State a thread is waiting for access to a
    CPU
  • Block State the thread is suspended while an
    interrupt is being processed
  • Running State the thread has control of the
    CPU.
  • The thread or its parent process terminates
    normally
  • An interrupt occurs

18
CPU Allocation
  • 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

19
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

20
CPU Allocation
21
CPU Allocation
22
Technology Focus
23
CPU Allocation
  • Priority-Based
  • First-come first served
  • The scheduler always dispatches the ready thread
    that has been waiting the longest.
  • Explicit priority
  • Uses a set of priority levels and assigns a level
    to each process or thread.

24
CPU Allocation
  • Shortest Remaining Time
  • Chooses the next process to be dispatched based
    on the expected amount of CPU time needed to
    complete the process.

25
Technology Focus
26
Memory Allocation
  • Single-Tasking Memory Allocation
  • Multitasking Memory Allocation
  • Memory Fragmentation
  • Noncontiguous Memory Allocation
  • Virtual Memory Management
  • Memory Protection
  • Memory Management Hardware

27
Memory Allocation
28
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.

29
Memory Allocation
30
Memory Allocation
  • Multitasking Memory Allocation
  • 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.

31
Memory Allocation
32
Memory Allocation
33
Memory Allocation
34
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

35
Memory Allocation
36
Memory Allocation
37
Memory Allocation
38
Memory Allocation
39
Technology Focus
40
Technology Focus
41
Interprocess Communication
42
Interprocess Communication
43
Interprocess Communication
44
Interprocess Communication
45
Interprocess Communication
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