Operating System Theory

1
Operating System Theory

• Guide to Operating Systems
• Third Edition

2
Understanding Operating Systems

• Operating system (OS)
• Set of basic programming instructions to computer
  hardware
• Forms layer of programming code on which most
  other functions of the computer are built
• Desktop operating system
• Typically installed on a PC type of computer used
  by one person at a time
• Computer may or may not be connected to a network

3
Understanding Operating Systems (continued)

• Server operating system
• installed on a more powerful computer that is
  connected to a network
• act in many roles to enable multiple users to
  access information, such as electronic mail,
  files, and software

4
Understanding Operating Systems (continued)

• Input/output (I/O)
• Basic functions which let other programs easily
  talk to the computer hardware

5
Understanding Operating Systems (continued)

• Operating systems perform the following tasks
• Handle input from the keyboard, mouse, and other
  input devices
• Handle output to the monitor and printer
• Handle communications using a modem
• Handle network communications, such as for a
  local network and the Internet

6
Understanding Operating Systems (continued)

• Operating systems perform the following tasks
  (continued)
• Control input/output for 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

7
Understanding Operating Systems (continued)

• Communicates directly with all of these devices
• Exchange information with specific hardware
  (chips) inside the computer
• Code (instructions) for this exchange is
  typically referred to as a device driver

8
Understanding Operating Systems (continued)

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

9
Understanding Operating Systems (continued)

• A separate device driver is usually present for
  each individual device inside the computer

10
Understanding Operating Systems (continued)

• A good example of a device is a compact disk read
  only Memory (CD-ROM) drive
• Device drivers that interface with your OS for
  other devices, include
• Floppy and hard disk drives
• Computer monitors
• Keyboards

11
Understanding Operating Systems (continued)

• Device drivers that interface with your OS for
  other devices, include
• Mouse and trackball devices
• Modems
• Printers and scanners
• Others are shown on page 5 of the textbook

12
Understanding Operating Systems (continued)

• Communicates with the application software
  running on the computer
• See Figure 1-3
• Application software
• Vague term it can mean a word processor,
  spreadsheet, database, computer game, etc

13
Understanding Operating Systems (continued)
14
Understanding Operating Systems (continued)

• Essential step to start a computer
• Load the Basic Input/Output System or BIOS
• Every PC has a BIOS stored in Read Only Memory or
  ROM
• Sample BIOS setup screen
• See Figure 1-4
• Turn on a PC
• Jumps to a startup program inside the BIOS

15
Understanding Operating Systems (continued)
16
Understanding Operating Systems (continued)
17
Understanding Operating Systems (continued)

• Elements in Figure 1-5 include the following
• Application software
• API (Application Program Interface)
• BIOS
• Operating system kernel
• Device drivers
• Resource managers
• Optional drivers
• Computer hardware

18
Understanding Operating Systems (continued)

• Common features of operating systems
• Interface between the computer hardware and
  application programs
• Act as an intermediary between the user and
  applications
• User interface into computer hardware and
  application programs
• Manage memory and central processor use
• Manage peripheral devices

19
Types of Operating Systems

• Functions of a computer
• Dictate what the OS will do and how it will do it
• An example
• Microwave oven needs device drivers for the LED
  (Light Emitting Diode) display, numeric keypad,
  and door close switches
• Operating systems are organized by
• Size, type, and purpose of the computer they run
  on

20
Types of Operating Systems (continued)

• PC-class computers
• Designed for individual users to perform tasks
• Example of complexity of PC operating systems
• Windows 95 had one millions lines of code
• Windows XP has 50 million

21
Types of Operating Systems (continued)

• Two main groups of computers
• Older, large computers with traditional operating
  systems
• Newer, smaller hardware with specialized
  operating systems

22
Time Sharing

• Mainframe-class computers
• Conduct massive calculations or manipulate huge
  amounts of data
• These systems are referred to as
• Time-sharing systems
• Time-sharing systems frequently conduct what are
  termed batch processes

23
Time Sharing (continued)

• Sequential processing
• Each process request is completed and the data
  returned before the next process is started

24
Time Sharing (continued)

• Time-sharing mainframe accessed by cables from
  terminals to a communications box connected to
  the mainframe, creating a multiuser system

25
Real-time Systems

• Real-time systems
• what most of us are familiar with today
• PC-based operating systems
• such as Windows XP and Mac OS X
• interact directly with the usereven multiple
  users and respond in real time

26
Real-time Systems (continued)

• Server running an OS such as NetWare to provide
  real-time access to multiple users over a network.

27
Multiuser Systems

• Multiuser environment
• Multiple users can do many different things on
  the machine at the same time
• All users are using one machine or a group of
  machines to do all their work
• Client/server system
• Newest types of large computing and operating
  system environments

28
Multiuser Systems (continued)

• Client/server operations
• Macintosh computer running Mac OS
• Minimally configured Windows XP computer
  connected to a network that includes a Windows
  2000 or 2003 server

29
A Short History of Operating Systems

• Computers used as large automated calculators
• Extremely large, often taking up entire rooms
• Scientists programmed computers to perform
  precise tasks
• Operating systems were rudimentary

30
A Short History of Operating Systems (continued)

• I/O devices were created, and computer memory
  capacity and speed increased
• Ability to share computer resources among various
  programs
• OS evolution in this era are long lost

31
A Short History of Operating Systems (continued)

• Notable players responsible for setting the stage
  for the full-featured functionality
• Digital Equipment Corporations PDP series
  computers
• Original UNIX was developed at ATT Bell Labs in
  1969 by Kenneth Thompson and Dennis Ritchie
• DEC VAX computers used VMS

32
A Short History of Operating Systems (continued)

• Mid sixties, a simple programming language was
  developed
• Dubbed BASIC, or Beginners All-purpose Symbolic
  Instruction Code

33
A Short History of Operating Systems (continued)

• 86-DOS
• Written by Tim Patterson for the new 8086
  microprocessor
• Evolved in 1980 into the Microsoft Disk Operating
  System, or MS-DOS
• IBM introduced the first PC in 1981
• Caused a revolution, because it was designed
  around an open standard
• Anyone was welcome to make PCs that worked like
  IBMs PC, or hardware that would work with it

34
A Short History of Operating Systems (continued)

• The Macintosh was introduced and it seemed to be
  light years ahead of the IBM PC
• Came with a standard graphical user interface
  (GUI)
• MS-DOS was still text-based
• Managed the computer memory closely for the
  software
• Microsoft, however, did not stay behind for long
• In 1990, Microsoft introduced Windows which
  provided a GUI and many of the same functions as
  the Mac OS

35
Single-Tasking versus Multitasking

• Multitasking
• Technique that allows a computer to run two or
  more programs at the same time

36
Single-Tasking versus Multitasking (continued)

• Most PCs have only one CPU chip
• does one thing at a time
• multitasking is 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
• cooperative multitasking shown in Figure 1-8

37
Single-Tasking versus Multitasking (continued)
38
Single-Tasking versus Multitasking (continued)

• Operating system
• hands over control to a program
• sits back
• waits for the program to hand control back to the
  operating system
• Preemptive multitasking
• illustrated in Figure 1-9
• OS is in control of the computer at all times

39
Single-Tasking versus Multitasking (continued)
40
Single-Tasking versus Multitasking (continued)

• A single-tasking operating system
• Executes one program at a time (see Figure 1-10)
• 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)

41
Single-Tasking versus Multitasking (continued)
42
Single-Tasking versus Multitasking (continued)

• Task-switching operating system
• offers many of the device management functions of
  the multitasking operating system
• can load multiple application programs at once
• figure 1-11 illustrates the concept of task
  switching

43
Single-Tasking versus Multitasking (continued)
44
Single-User versus Multiuser Operating Systems

• Multiuser operating systems
• run multiple programs at the same time
• allow multiple users to use an application
  simultaneously
• most use preemptive multitasking technology

45
Single-User versus Multiuser Operating Systems

• Desktop operating systems covered in this book
• initially were designed as single-user systems
• exceptions are UNIX and Linux - multi-user OS by
  design

46
Current Operating Systems

• Operating systems in this book are the most
  common in todays computing environments
• Windows 2000 Professional and Server
• Windows XP (Home, Professional, Tablet PC, and
  Media Center)
• Windows Server 2003

47
Current Operating Systems

• Operating systems in this book are the most
  common in todays computing environments
  (continued)
• The different flavors of UNIX/Linux operating
  systems, focusing particularly on Red hat
  Enterprise Linux 3.0
• NetWare 6.x
• Apple Macintosh Mac OS X (version 10.3 or Panther)

48
Summary

• An operating system provides the foundation upon
  which to run the components of a computer and
  execute applications
• Two common types of operating systems
• Desktop - may or may not be a network operating
  system
• Server - always a NOS

49
Summary (continued)

• Device drivers can extend the native functions to
  provide access and control over different types
  of devices\
• Printers
• CD-ROM drives.

50
Summary (continued)

• BIOS
• Low-level program code that operates between the
  computer hardware and a higher level operating
  system
• Initiate communications with hardware devices
• Perform hardware tests at startup
• Enable the startup of the higher-level operating
  system

51
Summary (continued)

• Operating system may be geared to run a large
  mainframe or a small PC-type of computer.
  However, the small PC-type systems now can be
  very powerful and are used in many places instead
  of mainframe systems.
• Operating systems can be understood in terms of
  characteristics
• Time sharing, real-time operation, and multiuser
  capabilities

52
Summary (continued)

• History of operating systems and computers
• Progression from physically huge computers
• Large computers
• Desktop-sized computers that have powerful
  processing capabilities and operating systems

53
Summary (continued)

• From the standpoint of the user
• The most significant advances in operating
  systems is the GUI
• Early operating systems tended to be
  single-tasking, but modern systems are largely
  multitasking.

54
Summary (continued)

• A true multiuser system
• Multiple users access and run a single
  application on a single computer at the same time

55
Summary (continued)

• Currently popular operating systems are the topic
  of this book
• Windows 2000/XP/Server 2003
• UNIX/Linux
• NetWare 6.x
• Mac OS X