Download Computers: Tools for an Information Age

Module 9: Operating Systems
Objective
What is an operating system (OS)? OS kernel, and basic functions
OS Examples: MS-DOS, MS Windows, Mac OS Unix/Linux
Features of modern OS
 Graphical operating system
 Multiple users, secure, stable
 Support networks
The main issues that an OS deals with
 Resource allocation, CPU time, memory management
 Multiprocessing, time-sharing, multiprogramming
Utility programs
Copyright © 2003 by Prentice Hall
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Systems Software and Application Software
Software are classified into categories according to their
functions: system software, application software
 System software are programs related to coordinating
computer operations, E.g.
Operating systems
Language translators

Convert program code to machine-readable form

Utility programs are those application
programs performing secondary chores
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What is an Operating System ?
A set of programs that lies between
applications software and the
hardware
 Manages computer’s resources
(CPU, memory, peripheral
devices)
 Establishes a user interface
Determines how user
interacts with operating
system
 Provides and executes services
for application software
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Kernel
The core of an OS is called kernel, which

Is loaded from hard drive into memory when
computer is booted and stays as long as the
computer is running
Booting refers to starting the computer

Manages the operating system
Loads other operating system programs from disk
storage as needed

Other programs referred to as nonresident
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Examples of Operating Systems
Platform: combination of computer
hardware and operating system software
Common Platforms
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PC with MS DOS (disk operating system), Windows
MAC OS
PC and Unix/Linux
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MS-DOS
Uses a command-line interface


Screen provides prompts for user. User types commands.
Five basic commands: dir, mkdir, cd, copy, del.
Largely replaced by graphical user interfaces
Not user-friendly
It is still there ( demo )
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Microsoft Windows
Began as an operating environment for MS-DOS
 Not a full-blown operating system; required MSDOS
Uses a graphical user interface
 Users can use DOS commands and interface
Now a complete family of operating systems
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Brief history of Windows OS
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Microsoft Windows 1.0, 1985
Microsoft Windows 2.0, 1987
Microsoft Windows 3.0, 1990
Windows 3.1, 1992
Windows 95, 1995
sells more than 1 Million copies within 4 days.
Windows 98
Microsoft Windows 2000
Microsoft Windows XP, 2001
Other MS Windows OS product lines
Windows NT, Windows Servers, Windows CE
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Graphical User Interface
User clicks an icon to perform
tasks
Start Menu in lower left corner
launches programs
Use menus to activate
commands
Other features


Long file names (up to 255
characters)
Plug and Play
Makes installing hardware
components easier
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Windows NT
Windows 98 and early is for single user
Windows NT was designed for corporate
networked environments

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Be able to handle many users
Engineered for scalability
Stronger security
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Windows 2000
The generation of Windows NT
One computer “serves” many users

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You identify yourself and the system knows
your preferences
You get “your” desktop and files, regardless of
which PC you use to log into the network
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Windows XP
Brings consumer and corporate versions of
Windows together into a single product

Has Home and Professional Editions
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Windows XP Enhancements
Improved user interface
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Much clearer and uncluttered desktop
More icons on redesigned Start Menu
Improved multimedia support
More personalization
Multiple user support

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User can log off, leaving programs running, and allow
another user to log on
Set up limited accounts for children to use; i.e., no
inappropriate games or no Internet access
Internet support and protection
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Windows CE
Scaled-back version of Windows 9x
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Designed to work on machines with small
screens and little, if any, storage
Used in Pocket PCs
Used in mobile phone
Used in embedded systems
Computer devices integrated into other products;
i.e., robots
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MAC OS
Designed for the Macintosh computer
First commercially successful GUI

Has served as the model for Windows and other GUI
products developed since then
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UNIX
Developed in 1971 for use on the DEC minicomputer
Not tied to any family of processors
 Runs on just about every type of system
Run on most main frame, supercomputers, Sun workstations, PC
Primary operating system in use on Internet servers

E.g. main web server of WLU is running Unix
Features

Very reliable, secure, stable system.
Character-based system with command-line interface, now comes
with several graphic user interface
Handles many simultaneous users easily
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Multiple tasks
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Linux
Similar to Unix, but in open source domain
Uses command-line interface
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Many companies have created a GUI to work with
Linux
Open-source concept
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Source code is free
Users can download, change, and distribute the
software
More stable than Windows
Applications relatively scarce
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Simple Unix/Linux Commands
ls, ls –l, ls -a
mkdir
cd, cd ..
pwd
mv
cp
rm
rmdir
cat, less, tail
grep
who
chmod
Network commands: telnet, ftp, ssh
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Operating Systems for Networks
Network operating system (NOS)

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Handles network functions
Make resources appear as though they were
running from client computers
Common systems
Functions
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Sharing resources (hard disks and printers)
Data security
Administrative control
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Examples of Network Operating Systems
Windows NT Server
Windows 2000 Server
Novell Netware
Unix
Linux
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The Main Task of an Operating Systems
Resource allocation: assigning and computer resources
to certain programs and processes for their use
This problem was raised when people designed the OS
for large computers with multiple users. It is also a
fundamental problem for modern OS for PC.
Main issues related to resource allocation
 Sharing the Central Processing Unit
 Sharing memory
 Sharing storage resources
 Sharing printing resources
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Sharing the CPU
Multiprogramming

Two or more programs executed concurrently
Programs take turns using the CPU
Event-driven
 An interrupt suspends processing to allow another
program to run
 After the second program runs, the operating system
returns the CPU to another program
Time-Sharing
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Programs take turns using the CPU
Time-driven
Each user is given a slice of time (fraction of a second)
CPU works only on that user’s tasks during its time slice
Response time: the time between typed request and
computer’s reply
Typically used in applications with many users
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Multiprocessing
The use of a powerful computer with multiple CPUs
 Supper computers usually have many processors
 Personal computers will soon have multiple
processors
Multiple programs run simultaneously

Each runs on its own processor
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Sharing Memory
Memory management

Divides memory into separate partitions

Allocates memory to programs
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Keeps programs separate from one another
Sharing memory
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Divides memory into foreground and background
Uses virtual storage
Also called virtual memory
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Foreground and Background
Foreground: for programs with high priority that
will receive more CPU time
Background: for programs with lower priority that
will receive less CPU time

Programs waiting to run are kept in queues
based on their priority
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Virtual Storage
Programs currently executed are stored on disk
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Portions of program brought into memory as needed
Minimizes the amount of memory needed
Can be implemented by paging
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Divide memory into small, fixed-size pages
Page table keeps track of memory locations
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Sharing Storage Resources
Keeps track of location of files
Responds to commands to manipulate files
Keeps track of input and output requests for files
 Processes them in the order received
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Sharing Printing Resources
Spooling: program writes a line to a disk file
rather than sending directly to a printer
 When file is completed, placed in queue
 File printed when printer becomes available
Allows program to complete execution much
more quickly
 Writing to disk much quicker than writing to
printer
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Utility Programs
Perform secondary chores
Examples
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File manager
File compression
Others
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File Manager
Stores files in a
hierarchical directory
structure
Windows uses
Windows Explorer
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File Compression
Reduces amount of
space a file requires

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Makes file take up less
space on disk
Takes less time to
transmit across
communication lines
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Other Utility Programs
Backup and Restore
 Backup: make copies of disks and store in a
safe place
 Restore: restore files from backups
Disk defragmenter: reorganizes disk so all files
are stored in contiguous locations
Device driver: handles commands for devices,
such as printers and storage devices
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