Transcript System Software

Chapter 6





6.1
6.2
6.3
6.4
6.5
System Software
Introduction of Operating System
Functions of OS
More About OS
Device Drive
Utility Software
6.1 Introduction of Operating System
Operating system (OS)
organise and control the resources of the PC
shield users from the underlying complex
operations
Layered software
architecture
6.1 Introduction of Operating System
BIOS: lowest layer of software that exercises
direct control over hardware
OS works between the applications and
BIOS.
Standard interface is established between
layers.
Each layer provides services and functions
for the above layers.
6.2 Functions of OS
Process management
Provide supervisory
calls for managing
processes
Administer the
allocation of system
resources between
processes
6.2 Functions of OS
Memory management
Manage the allocation of
memory among
processes
Control the memory
management hardware
Ensure that each
process has enough
memory to execute
6.2 Functions of OS
File system management
A collection of file system
objects are organised
Formatting and copying
disks
Displaying lists of files
Checking the amount of
used and free space
Copying, renaming,
deleting, moving and
sorting files
6.2 Functions of OS
Device management
share input and output
devices among the
processes requesting
them
6.2 Functions of OS
User interface
Users should know how to operate the user
interface
DOS: command-line driven OS
Graphical User Interface (GUI)
input commands by pointing at and clicking menus and
icons on screen
more user-friendly than text commands
enrich user interaction by incorporating multimedia
features
6.3 More About OS
Type of OS
Single-user, single-task
Single-user, multi-task
Multi-user
Multiprocessing
Real-Time Operating System (RTOS)
6.3 More About OS
Single-user, single-task OS
enable one user to do one thing at a time
effectively
e.g. DOS, Palm OS
Single-user, multi-task OS
allow a single user operate several programs at
the same time
commonly used in desktop and laptop computer
e.g. Windows XP
6.3 More About OS
Multi-user OS
allow many users to use computer’s resources
simultaneously
e.g. mainframe and supercomputers
Multiprocessing OS
support two or more CPUs running programs at
the same time
6.3 More About OS
Real-Time Operating System
support the execution of tasks within rigid time
constraints
e.g. industrial control systems, weapon systems
6.3 More About OS
Linux
efficient Unix-like
OS
provide PC users
a free or low-cost
OS
strong inherent
networking power
6.3 More About OS
Linux
adequate server capabilities for Web, FTP and
email
publicly open and is expanded by contributors
low demand on hardware resources
availability of many free applications
6.3 More About OS
Evolution of OS for
home PC
DOS
single user,
single task
system
command-line
driven OS
6.3 More About OS
Evolution of OS for
home PC
Windows 3.X
GUI operating
environments
need DOS to run
6.3 More About OS
Evolution of OS for
home PC
Windows 95
multitasking OS
improved graphical
interface
support networking,
plug and play
technology, long
filenames
contain tools to
access the Internet
6.3 More About OS
Evolution of OS for
home PC
Windows 98
upgraded version of
Windows 95
incorporate
Microsoft Internet
Explorer into the OS
provide better
Internet and
multimedia support
6.3 More About OS
Evolution of OS for
home PC
Windows ME
updated version of
Windows 98
rich set of multimedia
and entertainment
support
6.3 More About OS
Evolution of OS for
home PC
Windows XP Home
Edition
latest Windows OS for
home user
more intuitive visual
design
advanced digital media
features, firewall utility
and remote support
6.4 Device Drivers
Device driver
control a particular type of device attached to the
computer
convert I/O instructions of OS to messages
understood by device type
examples: printer, video adapters, CD-ROM
drives and disk drives
device driver layer: hide the differences among
I/O controllers from the OS
closely linked to the device controller
6.4 Device Drivers
Installing a device driver
6.5 Utility Software
Utility software
a program that provides an add-on to the
functions provided by the OS
make the computer easier and more reliable
not essential
e.g. virus protection, firewalls, disk repair /
recovery
6.5 Utility Software
Computer virus
programming code that causes unexpected and
undesirable events
transmitted through email attachments,
downloads, disk or CD
virus creator embeds codes into a program
virus activates and attaches itself to other
programs
some are annoying spanks
some destroy data or hard disk, corrupt programs
6.5 Utility Software
Types of viruses
System or boot-record viruses
File infector viruses
Macro viruses
Trojan horse
6.5 Utility Software
System or boot-record viruses
infect executable code found in disk
attach to the DOS boot sector on disks or Master
Boot Record of hard disk
File infector viruses
Some attach to program files (.COM or .EXE files)
Some infect any program for which execution is
requested
Some appear as wholly-contained programs or
scripts
6.5 Utility Software
Macro viruses
hidden within documents or data
unleashed when the macro is run
infect MS Word applications
Trojan horse
harmful code is embedded in seemingly harmless
programs or data
get control of system and do specified damages
6.5 Utility Software
Anti-virus programs
screen e-mail attachment
scan the whole system
identify and remove the virus found in memory,
storage media or incoming files
identify a virus by finding its virus signature
Signs of viruses
Unusual messages on screen
Decrease system performance
Missing data
Inability to access the hard drive
6.5 Utility Software
McAfee VirusScan
6.5 Utility Software
Anti-virus programs
Infected file is either removed or quarantined.
Latest virus definitions should be obtained.
Online anti-virus utility: protect PC connected to
the Internet permanently
automatically check for virus definition updates and
software updates
Delete the email with suspected infection
6.5 Utility Software
Firewall
A set of related programs protect the resources of
a private network from other networks
installed in network gateway server
work with a router program
determine each network packet whether forward it to
its destination
work with a proxy server
determine whether a data packet should be allowed to
pass through the wall
6.5 Utility Software
Packet filtering firewall
based on the addressing information found in
individual packets
compare the addressing information with its
programmed security policy
Stateful inspection firewall
extend the packet-by-packet filtering process to
include multi-packet flows
has the intelligence to track individual flows
6.5 Utility Software
Proxy Server
a gateway between the protected network and the
Internet
prevent packets from travelling directly between
the Internet and protected network
6.5 Utility Software
Disk cleanup utility
delete unwanted file
improve the performance of computers
6.5 Utility Software
Disk scan
detect and correct physical and logical errors on
hard disks and floppy disks
search for and remove unwanted files
Types of errors:
cross-link files: two or more files share the same
portion of the hard disk
lost file fragment: separate fragments of a larger file
invalid file information: incorrect information about
file names, data and time
6.5 Utility Software
Disk defragmenter
rearrange files, programs and unused space on
hard disk
increase the speed of OS and programs
6.5 Utility Software
How disk defragmenter is formed?
Each file is stored
as a linked list of
cluster in hard disk
F3 is deleted and
space is left.
F5 with 3 clusters
is split into two
portion
6.5 Utility Software
Efficiency of hard disk decreases with the
number of fragmented files
Disk defragmenter in Windows
rearrange the fragmented files and unused space
help restore the efficiency
improve the access time
6.5 Utility Software
END