Chapter 13 Operating Systems: An Overview

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Chapter 13Operating Systems An Overview

• The Architecture of Computer Hardware and Systems
  Software An Information Technology Approach
• 3rd Edition, Irv Englander
• John Wiley and Sons ?2003
• Wilson Wong, Bentley College
• Linda Senne, Bentley College

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Fundamental Purpose of OS

• To control and operate the hardware in an
  efficient manner
• To allow the user powerful access to the
  facilities of the machine

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13.1 - Bare Bones Computer System

• Does not load instructions into main memory
• No user interface except for I/O routines
  provided with executing program
• Is idle when waiting for user input
• No facility to store, retrieve, or manipulate
  files
• No ability to control peripheral devices
• Can run only one program at a time

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Integrated Computer Environment
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13.2 - Operating System

• A collection of computer programs that integrate
  the hardware resources of the computer and make
  those resources available to the user, in a way
  that allows the user access to the computer in a
  productive, timely, and efficient manner.
• System manager intermediary between the user,
  the users programs, and the hardware.

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Operating System Three Basic Services

• Accepts and executes commands and requests from a
  user and a users program
• Manages, loads, and executes programs
• Manages hardware resources of the computer

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Operating System Additional Services

• Provides interfaces for the user and the users
  programs
• File support services
• I/O support services
• Means of starting the computer
• Bootstrapping or booting the computer or Initial
  Program Load (IPL)
• Handles all interrupt processing
• Network services
• Provides tools and services for concurrent
  processing (simulate the simultaneous execution
  of multiple programs)

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Additional Services Required by Concurrent
Processing

• Allocates resources such as memory, CPU time, and
  I/O devices to programs
• Protects users and programs from each other and
  outsiders and provides for inter-program
  communication
• Provides feedback to the system administrators to
  permit performance optimization of the computer
  system

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OS Parts

• Memory Resident
• Always loaded in memory
• Commonly called the kernel
• Contains essential services required by other
  parts of the operating system and applications.
• Typically responsible for managing memory
  management, processes and tasks, and secondary
  storage
• Memory Non-resident
• Applications
• Infrequently used programs, software tools, and
  commands
• Bootstrap program (BIOS)
• Diskless workstations or thin clients
• Programs, including the OS, are located on
  another computer on the network

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13.7 -Types of Operating Systems

• Single-user
• Single-tasking systems
• Multi-tasking systems
• Multi-user, multitasking systems
• Distributed systems
• Network servers
• Embedded systems
• Real-time systems

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Categorization by Degree of Activity

• OS Degree of Activity
• Interactive (what you are use to!)
• Also known as conversational systems
• Batch processing (billing, backup)
• User submits programs or jobs for processing
• Little to no user interaction
• Event driven
• Interrupts or service requests

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Hardware and the OS

• A hardware platform may support a variety of
  operating systems
• An operating system may work on a variety of
  platforms
• A standard operating system that works on
  different hardware
• Provides program and file portability
• Enables user efficiency through recognizable
  interface
• Is implemented through a systems programming
  language like C or C as opposed to assembly
  language

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13.3 - Single Job Processing

• Only one program is loaded into memory and
  executed (obsolete)
• Example MS-DOS
• MS-DOS had three memory resident components
• Command interface shell
• I/O routines, including BIOS
• File management system
• Users program in control (once the program is
  started OS is out of the picture)

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OS Regains Control

• When program is finished control is
  transferred back to the command interpreter
• If the users program requests I/O it makes a
  request to OS
• Program places a request number in a previously
  agreed upon register or memory location and then
  jumps to the OS
• The user wishes to stop the program execution
  via a keyboard interrupt
• System malfunctions

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Single Job Processing

• Disadvantages
• Lack of security
• Programs can overwrite the resident OS
• Programs can write directly to I/O devices
• System provides minimum memory management and no
  scheduling
• CPU is often idle awaiting the completion of I/O
  operations

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13.4 - Concurrent Operations

• Multitasking (multiprogramming) vs.
  multiprocessing
• Multitasking manipulating multiple programs on
  a single CPU
• Multiprocessing manipulating one to many
  programs on multiple CPUs
• Concurrent processing vs. simultaneous processing
• Concurrent processing appears to be processing
  simultaneously.
• Simultaneous processing occurs at the same time

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Achieving Multitasking

• While one program is waiting for I/O to take
  place, another program is using the CPU to
  execute instructions.
• Time-slicing - the CPU may be switched rapidly
  back and forth between different programs
• Dispatching is the process of selecting which
  program to run at any given instant

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Sharing the CPU during I/O Breaks

• I/O represents a large percentage of a typical
  programs execution

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Time-sharing the CPU
Time slicing
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13.5 - Services and Facilities

• Command processor application program interface
  and user interface
• File management system
• I/O control system
• Process control management and inter-process
  communication
• Memory management
• Scheduling system
• Secondary storage management
• System protection management
• Network management, communication support, and
  communication interfaces
• System Administration

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User Interface and Command Execution Services

• Types of user interfaces
• CLI - Command Line Interface
• GUI - Graphical User Interface
• Menu environment
• Shell
• User interface and command processor that
  interacts with the kernel
• UNIX C, Bourne and Korn shells
• Command Languages
• IBM Mainframes JCL
• MS Windows BAT files, Windows Scripting Host
• UNIX shell scripts

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File Management

• File - logical unit of storage
• Basic file management system provides
• Directory structures for each I/O device
• Tools to copy and move files
• Information about each file in the system and the
  tools to access that information
• Security mechanisms to protects files and control
  access
• Additional file management features
• Backup, emergency retrieval and recovery
• File compression
• Transparent network file access
• auditing

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I/O Services andProcess Control Management

• I/O services
• Startup configuration
• Device drives that implement interrupts and
  provide other techniques for handling I/O
• Plug and play hot swapping, hot plugging
• Process control management
• A process is an executing program
• A thread is an individually executable part of a
  process
• Interprocess messaging services (processes
  cooperate with each other by sending messages)

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Memory Management

• Keeps track of memory
• Identifies programs loaded into memory
• Amount of space each program uses
• Available remaining space
• Prevents programs from reading and writing memory
  outside of their allocated space
• Maintains queues of waiting programs
• Allocates memory to programs that are next to be
  loaded
• De-allocates a programs memory space upon
  program completion

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Scheduling

• High-level scheduling
• Placed in queue based on level of priority and
  eventually executed
• Dispatching
• Actual selection of processes that will be
  executed at any given time
• Preemptive uses clock interrupts
• Non-preemptive program voluntarily gives up
  control
• Context switching
• Transfer control to the process that is being
  dispatched
• Processing requirements
• CPU vs. I/O bound
• CPU require an extensive amount of CPU time
• I/O bound require very little CPU processing
  time

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Secondary Storage and Security

• Secondary storage management
• Optimizes completion of I/O tasks for efficient
  disk usage
• Optimization may be provided by a combination of
  I/O hardware and OS software
• Security and protection services
• Protect OS from users
• Protect users from other users
• Prevent unauthorized entry to system
• Prevent unauthorized system use by authorized
  users

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Network and Communication Services

• TCP-IP protocol suite
• Locate and connect to other computers
• Access files, I/O devices, and programs from
  remote systems
• Support distributed processing
• Network Applications
• Email, remote login, Web services, streaming
  multimedia, voice over IP telephony, VPN
• Interface between communication software and OS
  I/O control system that provides network access

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System Administration Support

• System configuration and setting group
  configuration policies
• Adding and deleting users
• Modifying user privileges
• System security
• Files systems management

• Network administration
• Backups
• Software installations and upgrades
• OS installations (system generation), patches,
  and upgrades
• System tuning and optimization

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13.6 OS Organization

• Three common configuration models
• Monolithic
• Layered or hierarchical
• microkernel

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Monolithic

• The operating system programs simply interact as
  required to perform functions.
• The critical functions within the kernel operate
  in protected mode
• The remainder of the functions operate in user
  mode.
• The shell is separate from the kernel and serves
  as an interface

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Monolithic Configuration

• Drawback stability and integrity of the system
• Defect in kernel program can crash entire system
• Examples
• UNIX
• Windows NT

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Hierarchical Configuration

• Outer most layers are the most visible to the
  users
• Each layer calls the next innermost layer
• Require careful design services must be layered
  in a way such that all requests move inward

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Hierarchical

• Requests passthrough intermediatelayers
• Examples
• Multics
• Data General

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Microkernel Configuration

• Recent
• Based on small protected kernel that provide
  minimum essential functionality
• Constitutes a client-server system where client
  and server both reside on the same system

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Microkernel Configuration

• Operating system services outside of the
  essential functionality are performed by programs
  in user mode.
• Each program acts as a server that performs
  specific operating system tasks upon request of
  application programs as well as other OS programs
  (the client in this model)
• Clients request services by sending messages
  directly the microkernel.
• The microkernel passes the message to the
  appropriate server, who performs the function and
  replies by sending a message back to the client

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Microkernel

• Minimum essential functionality
• Client-server system on same system
• Clients request services from microkernel which
  passes message onto appropriate server

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Mach OS Kernel

• Microkernel implementation
• Includes
• Message passing
• Interrupt processing
• Virtual memory management
• Scheduling
• Basic set of I/O drivers
• Macintosh OS X

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13. 8 - Bootstrapping

• Execution begins with bootstrap loader
  (mini-loader, IPL) stored in ROM
• Looks for OS program in a fixed location
• Loads OS into RAM
• Transfers control to starting location of OS
• Loader program in OS used to load and execute
  user programs back

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Bootstrapping

• Cold vs.warm boot(does not retest the system)