Operating System Theory

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Operating System Theory

• Guide to Operating Systems Second Edition

2
Objectives

• After reading this chapter and completing the
  exercises you will be able to
• Understand what an operating system does
• Describe the types of operating systems
• Understand the history of operating system
  development
• Discuss single tasking versus multitasking
• Differentiate between single-user and multi-user
  operating systems
• List and briefly describe current operating
  systems

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Understanding Operating Systems

• An operating system (OS) is a set of basic
  programming instructions to the lowest levels of
  computer hardware, forming a basic layer of
  programming code on which most other functions of
  the computer are built
• A desktop operating system typically is one
  installed on a PC type of computer that is used
  by one person at a time, and that may or may not
  be connected to a network

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Understanding Operating Systems

• A server operating system is usually on a more
  powerful computer that is connected to a network,
  and can act in many roles to enable multiple
  users to access information, such as electronic
  mail, files, and software
• In its lowest form, the operating system takes
  care of what are known as basic input/output
  (I/O) functions, which let other programs easily
  talk to the computer hardware

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Understanding Operating Systems

• Operating systems perform the following tasks
• Handle input from the keyboard and mouse
• Handle output to the screen and printer
• Handle communications using a modem
• Handle network communications, such as for the
  Internet
• Control input/output with all bus devices, such
  as a network interface card
• Control information storage and retrieval using
  various types of disk and CD-ROM drives
• Enable multimedia use for voice and video
  reproduction, such as playing music through
  speakers

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Understanding Operating Systems

• The operating system communicates directly with
  all of these devices
• Some operating system programs exchange
  information with specific hardware (chips) inside
  the computer
• This code is typically referred to as a device
  driver

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Understanding Operating Systems

• A device driver translates computer code to
  display text on a screen, or translates movements
  of a mouse into action

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Understanding Operating Systems

• A separate device driver is usually present for
  each individual device inside the computer, as
  shown in Figure 1-2

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Understanding Operating Systems

• A good example of a device a compact disk read
  only Memory (CD-ROM) drive
• You may encounter device drivers that interface
  with your operating system for other devices,
  including
• Floppy and hard disk drives
• Computer monitors
• Keyboards
• Mouse and trackball devices
• Modems
• Scanners
• Others are shown on page 4 of the textbook

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Understanding Operating Systems

• In addition to communicating with computer
  hardware, the operating system communicates with
  the application software running on the computer,
  as shown in Figure 1-3
• Application software is a fairly vague term it
  can mean a word processor, spreadsheet, database,
  computer game, or many types of other applications

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Understanding Operating Systems
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Understanding Operating Systems

• The general operating system we describe provides
  only the most basic input and output functions,
  so it is called a Basic Input/Output System, or
  BIOS
• Every PC has a BIOS, which is stored in Read Only
  Memory, or ROM
• Figure 1-4 shows a sample BIOS setup screen on a
  computer
• Whenever you turn on your PC, the machine wakes
  up and jumps to a startup program inside the BIOS

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Understanding Operating Systems

• This program initializes the screen and keyboard,
  tests some central computer hardware, such as the
  central processing unit (CPU) and memory,
  initializes the floppy drive and other disk
  drives, and then loads other parts of the
  operating system that can provide more advanced
  functionality for application programs

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Understanding Operating Systems

• Figure 1-5 shows a general conceptual drawing of
  various operating system components

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Understanding Operating Systems

• The elements in Figure 1-5 include the following,
  from the application down
• Application software
• API (Application Program Interface)
• BIOS
• Operating system kernel
• Device drivers
• Resource managers
• Optional drivers
• Computer hardware

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Understanding Operating Systems

• Some features that most operating systems have in
  common are
• Provide an interface between the computer
  hardware and application programs
• Act as an intermediary between the user and
  applications
• Provide a user interface into computer hardware
  and application programs
• Manage memory and central processor use
• Manage peripheral devices, such as printers,
  monitors, keyboards, and modems

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Types of Operating Systems

• The functions a computer requires, to a large
  extent, dictate what the operating system will do
  and how it will do it
• As an example, the computer in a microwave oven
  needs device drivers for the LED (Light Emitting
  Diode) display, numeric keypad, and door close
  switches
• In general, operating systems are organized by
  the size, type, and purpose of the computer on
  which they run

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Types of Operating Systems

• PC-class computers are designed for individual
  users to perform tasks, such as word processing,
  database and spreadsheet management, and
  networking with other computers
• One example of how PC operating systems have
  become more complex is the comparison of lines of
  code in Windows 95 to Windows XP
• One way to look at computer operating system
  differences is to consider that there are really
  two main groups of computers older, large
  computers with traditional operating systems, and
  newer, small hardware with similar but
  specialized operating systems

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Types of Operating Systems

• Mainframe-class computers are used to conduct
  massive calculations or manipulate huge amounts
  of data
• These systems are referred to as time-sharing
  systems
• These time-sharing systems, and other large
  computers, frequently conduct what are termed
  batch processes

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Types of Operating Systems

• Todays smaller, interactive systems are more
  prone to use sequential processing, where each
  process request is completed and the data
  returned before the next process is started
• Real-time systems are what most of us are
  familiar with today
• PC-based operating systems, such as Windows 98 or
  Windows XP, interact directly with the usereven
  multiple users (on shared drives)and respond in
  real time with the required information

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Types of Operating Systems

• In this environment, multiple users can do many
  different things on the machine at the same time
• Still, all users are using one machine or a group
  of machines to do all their work
• This is known as a multi-user environment
• One of the newest types of large computing and
  operating system environments is known as the
  client/server system

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Types of Operating Systems

• A Macintosh computer running Mac OS, or a
  minimally configured Windows 2000 computer
  connected to a network that includes a Windows
  NT, 2000, or .NET server, for example is well
  suited for client/server operations
• Taking client/server systems a step further is
  Microsofts .NET architecture
• .NET incorporates the Internet and focuses on
  integrating data and user functions so that they
  can be accomplished at any location on many kinds
  of devices, including handheld devices and cell
  phones

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A Short History of Operating Systems

• Initially, computers were used as large automated
  calculators to solve all sorts of mathematical
  and statistical problems
• Computers were extremely large, often taking up
  entire rooms
• Scientists programmed these computers to perform
  precise tasks, the exact tasks for which they
  were built
• The operating systems were rudimentary, often not
  able to do more than read punch cards or tape,
  and write output to Teletype machines

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A Short History of Operating Systems

• Input and output devices were created, and
  computer memory capacity and speed increased
• The next evolution was the ability to share
  computer resources among various programs
• Some of the operating systems that evolved in
  this era are long lost to all but those who
  worked directly with them
• But there are some notable players that were
  responsible for setting the stage for the
  full-featured functionality we take for granted
  today

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A Short History of Operating Systems

• Digital Equipment Corporations PDP series
  computers, for example, ran the DEC operating
  systems, simply known as OS, in one version of
  another
• A popular one was OS/8, which came in various
  versions, such as Release 3Q, and was released in
  1968
• The original UNIX was developed at ATT Bell Labs
  in 1969 by Kenneth Thompson and Dennis Ritchie as
  an improvement on Multics

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A Short History of Operating Systems

• Later Digital VAXs used VMS, a powerful,
  multitasking, multi-user system that was strong
  on networking
• In the mid sixties, right after the first
  interactive computer game was invented at MIT, a
  simple programming language was developed, aimed
  at the non-programmer
• It was dubbed BASIC, or Beginners All-purpose
  Symbolic Instruction Code

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A Short History of Operating Systems

• 86-DOS, which was originally written by Tim
  Patterson for the new 8086 microprocessor,
  evolved in 1980, through a cooperative effort
  between Patterson and Microsoft, into the
  Microsoft Disk Operating System, or MS-DOS
• IBM introduced the first PC in 1981, it caused a
  revolution, because it was designed around an
  open standard
• Anyone who wanted to was welcome to make PCs that
  worked like IBMs PC, or hardware that would work
  with it

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A Short History of Operating Systems

• The Macintosh was introduced in 1984, and it
  seemed to be light years ahead of the IBM PC
• Its operating system came with a standard
  graphical user interface (GUI), at a time when
  MS-DOS was still text-based
• Also, the Macintosh OS managed the computer
  memory closely for the software, something MS-DOS
  did not do
• Microsoft, however, did not fall far behind
• In 1990, Microsoft introduced an extension to its
  DOS operating system, called Microsoft Windows
  which provided a GUI and many of the same
  functions as the Mac OS

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Operating System Releases
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Operating System Releases
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Operating System Releases
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Single-Tasking versus Multitasking

• In practice, almost every resource in the
  computer, such as the memory and the
  microprocessor (central processing unit or CPU),
  is managed by the operating system
• One of the major reasons for giving operating
  systems so much control over resources is to
  facilitate multitasking, a technique that allows
  a computer to run two or more programs at the
  same time

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Single-Tasking versus Multitasking

• Since most personal computers have only one CPU
  chip, which can in general only do one thing at a
  time, multitasking is generally achieved by
  splitting processor time between applications,
  switching so rapidly that the user is not aware
  of any discontinuity
• There are two general types of multitasking
• The first method is known as cooperative
  multitasking

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Single-Tasking versus Multitasking

• In this method, the operating system hands over
  control to a program, sits back, and waits for
  the program to hand control back to the operating
  system
• A better method is the second alternative,
  preemptive multitasking, illustrated in
  Figure 1-7
• In this scenario, the operating system is in
  control of the computer at all times

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Cooperative Multitasking Basics
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Preemptive Multitasking Basics
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Single-Tasking versus Multitasking

• A single-tasking operating system executes one
  program at a time (see Figure 1-8)
• To do something else, one program must be
  stopped, and a new program must be loaded and
  executed
• New single-tasking operating systems are found
  only in computers with very limited processor
  capacity, such as Personal Digital Assistants
  (PDAs)

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Single-Tasking Operating System
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Single-Tasking versus Multitasking

• A special note must be made of a hybrid system
  called a task-switching operating system
• This system offers many of the device management
  functions of the multitasking operating system,
  and it can load multiple application programs at
  once
• You can see the concept of task switching in
  Figure 1-9

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Task Switching
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Single-User versus Multi-User Operating Systems

• Some operating systems, in addition to being able
  to run multiple programs at the same time with
  multitasking technology, allow multiple users to
  use an application simultaneously
• These are known as multi-user operating systems
• Most multi-user systems use preemptive
  multitasking technology
• The desktop operating systems covered in this
  book initially were designed as single-user
  systems with the exception of UNIX, which is a
  multi-user operating system by design

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Current Operating Systems

• The operating systems surveyed in this book are
  the most common in todays computing
  environments, and they fall into several
  families
• Windows 95, Windows 98, and Windows Me
• Windows NT, Windows 2000, Windows XP, and Windows
  .NET Server
• The different flavors of UNIX operating systems
• Apple Macintosh Mac OS systems

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Summary

• You were introduced to the concept of device
  drivers, and the functions the operating system
  provides to application programs
• The types of operating systems in use were
  briefly discussed, as well as the differentiation
  that can be made based on the computer
  environment in which the operating system is used
• A short operating system history touched on some
  of the highlights in computer development from
  the standpoint of operating systems

44
Summary

• Also introduced were single-tasking operating
  systems, which run only one application at a
  time, and multitasking operating systems, which
  can run multiple applications at once
• Finally, some modern PC operating systems you
  will find in use today were described
• This theoretical beginning will provide a good
  background for the following chapter