Operating System Theory
Guide to Operating Systems
Third Edition
Objectives
After reading this chapter and completing the
exercises you will be able to:
• Understand how an operating system works
• Describe the types of operating systems
• Understand the history of operating system
development
• Discuss single-tasking versus multitasking
• Differentiate between single-user and multiuser
operating systems
• List and briefly describe current operating systems
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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
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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
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Understanding Operating
Systems (continued)
• Input/output (I/O)
– Basic functions which let other programs easily
talk to the computer hardware
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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
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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
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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
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Understanding Operating
Systems (continued)
• A device driver translates computer code to
display a screen, or translates movements of
a mouse into action
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Understanding Operating
Systems (continued)
• A separate device driver is usually present for
each individual device inside the computer
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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
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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
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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
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Understanding Operating
Systems (continued)
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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
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Understanding Operating
Systems (continued)
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Understanding Operating
Systems (continued)
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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
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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
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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
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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
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Types of Operating Systems
(continued)
• Two main groups of computers
– Older, large computers with traditional operating
systems
– Newer, smaller hardware with specialized
operating systems
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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
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Time Sharing (continued)
• Sequential processing
– Each process request is completed and the data
returned before the next process is started
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Time Sharing (continued)
• Time-sharing mainframe accessed by cables from
terminals to a communications box connected to the
mainframe, creating a multiuser system
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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 user—even
multiple users and respond in real time
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Real-time Systems
(continued)
• Server running an OS such as NetWare to provide
real-time access to multiple users over a network.
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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
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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
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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
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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
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A Short History of Operating
Systems (continued)
• Notable players responsible for setting the stage
for the full-featured functionality
– Digital Equipment Corporation’s PDP series computers
– Original UNIX was developed at AT&T Bell Labs in 1969
by Kenneth Thompson and Dennis Ritchie
– DEC VAX computers used VMS
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A Short History of Operating
Systems (continued)
• Mid sixties, a simple programming language was
developed
– Dubbed BASIC, or Beginner’s All-purpose Symbolic
Instruction Code
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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 IBM’s PC, or hardware that would work with it
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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
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Single-Tasking versus
Multitasking
• Multitasking
– Technique that allows a computer to run two or more
programs at the same time
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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
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Single-Tasking versus
Multitasking (continued)
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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
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Single-Tasking versus
Multitasking (continued)
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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)
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Single-Tasking versus
Multitasking (continued)
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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
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Single-Tasking versus
Multitasking (continued)
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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
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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
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Current Operating Systems
• Operating systems in this book are the most
common in today’s computing environments:
– Windows 2000 Professional and Server
– Windows XP (Home, Professional, Tablet PC, and Media
Center)
– Windows Server 2003
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Current Operating Systems
• Operating systems in this book are the most
common in today’s 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)
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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
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Summary (continued)
• Device drivers can extend the native functions to
provide access and control over different types of
devices\
– Printers
– CD-ROM drives.
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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
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Summary (continued)
• Operating system may be geared to run a large mainframe
or a small PC-type of computer. However, the small PCtype 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
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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
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Summary (continued)
• From the standpoint of the user
– The most significant advances in operating systems
is the GUI
• Early operating systems tended to be singletasking, but modern systems are largely
multitasking.
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Summary (continued)
• A true multiuser system
– Multiple users access and run a single application on a
single computer at the same time
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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
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