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Introdution Of Computers


1. What is a Computer?1. [ 2. Basic Operations & Functioning of a Computer system 3. Memory –Types of Memory Hardware –Types of Hardware Software –Types of Software 4. Characteristics of Computers 5. Classification / Types of Computers 6. Overview of Operating System - Basic functions Operating Systems – PowerPoint PPT presentation

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Title: Introdution Of Computers

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  • In this Chapter you will learn about
  • 1. What is a Computer?
  • 2. Basic Operations Functioning of a Computer
  • Memory Types of Memory
  • Hardware Types of Hardware
  • Software Types of Software
  • 4. Characteristics of Computers
  • 5. Classification / Types of Computers
  • 6. Overview of Operating System
  • - Basic functions Operating System

7. Computer Virus - Definition - History /
Background - Symptoms of Virus Attack - Virus
Languages - Classification - How can Computer
infected - Location of Virus 8. Applications
of Computers 9. Buying a Computer
Definition of a Computer A computer is an
electronic device that can perform arithmetic
Logical operations at high speed. A Computer is
an electronic device which processes information
based upon the instructions provided , and
generates the desired output. On a computer user
can work on any kind of data Text, Numeric,
alpha numeric, images, pictures, sound video
clippings etc. , now
days, most of the
computer applications are non-numeric.
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  • Computer System is composed of the following
  • each of the components plays an important role in
  • Input devices
  • Output devices
  • Central processing unit (CPU) (ALU, CU, Memory

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Commonly Used Input Devices Keyboard Point Draw
Devices (Ex. Joy stick, Mouse, Track Ball, Light
Pen, Touch Screen) Data Scanning Devices
(Scanner) Digitizer Speech Recognition
Devices Vision based Devices
Input Devices
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Commonly Used Output Devices
  • Monitors ( Cathode ray Tube (CRT), LCD, TFT )
  • Printers ( Dot Matrix, Inkjet, Laser Printers)
  • Plotters
  • Screen Image Projectors
  • Voice Response System

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Output Devices
Laser Printer
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The Central Processing Unit (CPU)
The Central Processing Unit is a silicon chip
that is the brain of of a computer system.
It executes program instructions and data and
controls all the devices within the machine
Its internal organisation (architecture)
consists of 3 main parts
  • Control unit (CU)
  • Arithmetic and Logic unit (ALU)
  • Registers

AMD Athlon XP 2200
Intel Pentium 4 2.533 Ghz Socket 478
Inside the CPU
The Control Unit
The CU sends signals to other parts of the
It manages fetch, decode and execute program
It synchronises the whole system by telling
devices what to do and when to do it
The Arithmetic and Logic Unit
The ALU is where data is actually processed in
the CPU
Processing data in the ALU involves doing
arithmetic calculations e.g. add, subtract,
multiply, divide etc.
It also involves logical comparisons like AND, OR
etc. using electronic circuitry
The ALU uses special arithmetic registers to
temporarily store data and results of
calculations e.g. the accumulator
The Registers
The Registers are very fast storage locations
inside the processor itself. There are many
registers including
  • memory address register (MAR) holds the address
    of a location in memory
  • memory data register (MDR) holds data just read
    from or written to memory
  • program counter (PC) holds the address of the
    next instruction to be fetched
  • Instruction register (IR) holds the current
    instruction being executed
  • general purpose registers can be used by

The central processing unit (CPU) is the center
of all computer-processing activities, where all
processing is controlled, data are manipulated,
arithmetic computations are performed, and
logical comparisons are made. The CPU consists of
the control unit, the arithmetic-logic unit
(ALU), and the primary storage (or main memory).
Because of its small size, the CPU is also
referred to as a microprocessor. How a
Microprocessor Works- The CPU operates like a
tiny factory. Inputs come in and are stored until
needed, at which point they are retrieved and
processed and the output is stored and then
delivered somewhere. Figure illustrates this
process, which works as follows

The inputs are data and brief instructions
about what to do with the data. These
instructions come from software in other parts of
the computer. Data might be entered by the user
through the keyboard, for example, or read from a
data file in another part of the computer. The
inputs are stored in registers until they are
sent to the next step in the processing. Data
and instructions travel in the chip via
electrical pathways called buses. The size of the
busanalogous to the width of a
highwaydetermines how much information can flow
at any time. The control unit directs the flow
of data and instructions within the chip. The
arithmetic-logic unit (ALU) receives the data and
instructions from the registers and makes the
desired computation. These data and instructions
have been translated into binary form, that is,
only 0s and 1s. The CPU can process only binary
data. The data in their original form and the
instructions are sent to storage registers and
then are sent back to a storage place outside the
chip, such as the computers hard drive
(discussed below). Meanwhile, the transformed
data go to another register and then on to other
parts of the computer (to the monitor for
display, or to be stored, for example).
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Storage Devices
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Computer Hardware
Hardware is one that is tangible. The storage
devices (Hard disk, CDs etc.,), mouse, keyboard
CPU and display devices (Monitor) are Hardware.
Software Software is the collection of
program/a set of instructions software acts as an
interface between the user and the computer i.e.
Hardware A software or a program can be defined
as a complete set of instructions written by the
programmer which enables the computer to obtain
the solution to a problem The software used by a
computer classified into 1. Systems
Software 2. Applications Software 3. Utility
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System Software includes the Operating System
and all the utilities that enable the computer to
function. System software is a term
referring to any computer software which manages
and controls the hardware so that application
software can perform a task. Example
Operating Systems, Compiler, Loader, Linker,
Utility Software - is the a specific tools
that are used while developing a program or
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Session - II
  • In this Session we are going to cover following
  • Classification of Computer
  • Overview of Operating System
  • - Basic functions Operating System
  • Computer Virus
  • - Definition
  • - History / Background
  • - Symptoms of Virus Attack
  • - Virus Languages
  • - Classification
  • - How can Computer infected
  • - Location of Virus
  • 4. Applications of Computers
  • 5. Buying a Computer

Types of computer
Analog computer
  • Analog computer measures and answer the questions
    by the method of HOW MUCH. The input data is
    not a number infect a physical quantity like tem,
    pressure, speed, velocity.
  • Signals are continuous of (0 to 10 V)
  • Accuracy 1 Approximately
  • High speed
  • Output is continuous
  • Time is wasted in transmission time

Analog computer
Digital Computers
  • Digital computer counts and answer the questions
    by the method of HOW Many. The input data is
    represented by a number. These are used for the
    logical and arithmetic operations.
  • Signals are two level of (0 V or 5 V)
  • Accuracy unlimited
  • low speed sequential as well as parallel
  • Output is continuous but obtain when computation
    is completed.

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  • They are similar to PCs but with more memory and
    a high speed processor
  • They are intended to support network operating
    systems and network applications.
  • They are used in architectural design, video
    editing, animations etc.

A stand-alone computer is called a workstation on
a network
  • Large computers both in terms of physical size as
    well as computations
  • They support huge numbers of users
  • Basically used to store and process huge amount
    of data
  • Not all organizations can offered to maintain one
    mainframe. Take service of one vendor

  • In Past Mainframes were huge computers that could
    fill an entire room. It was
  • built by IBM in1950s
  • Mainframes are capable of supporting even
    thousands of users simultaneously
  • Mainframes are powerful and generally expensive
    as normal computers. It has
  • 8 or less processors
  • Large corporations, where data processing is
    centralized and large databases
  • are maintained, often use mainframe computers.
  • Applications that run on a mainframe can be large
    and complex, allowing for
  • data and information to be shared throughout
    the organization. process
  • multiple instructions simultaneously.

  • Used in scientific and engineering applications
    those handling huge data and do a great amount of
  • Extremely fast in operation (_at_ 1 trillion
  • Fastest, costliest and powerful computer
    available today
  • Application involves, weather forecasting,
    military applications, electronic design etc.

  • Supercomputers are the computers with the most
    processing power. The category of computers that
    includes the fastest and most powerful (most
    expensive) ones available at any given time.
  • In 1960 Ist Supercomputer built in US Department
    of Defense
  • Supercomputers supports multiprocessing, so that
    computer can perform
  • multiple operations simultaneously
  • The primary application of supercomputers has
    been in scientific research
  • military work to solve complex mathematical
    equations and computational
  • problems very quickly.
  • Supercomputers are especially valuable for large
    simulation models of real-
  • world phenomena, where complex mathematical
    representations and
  • calculations are required, or for image
    creation and processing.

  • Supercomputers can monitor action reaction of
    million of atom when they
  • interacts
  • multiple operations simultaneously .
  • IBM, Silicon Graphics, Intel ,Thinking Machine
    are the major manufacturer of
  • Supercomputers
  • Thinking Machine developed Supercomputer called
    as Connection Machine
  • which has 64,000 processors price is
  • decrease.
  • Super computers consumes the light of about100
  • Use of Supercomputer
  • Computational chemistry
  • Climate prediction Weather forecasting
  • Crash analysis
  • Cryptography
  • Nuclear simulation
  • Structural analysis
  • Space Research

Supercomputers 1.Columbia (NASA, USA) 2.Earth
Simulator (Japan) 3.MareNostrum
(Spain) 4.Thunder (USA) 5.Param (IND)
  • A server is one for which many PCs are connected.
  • It has large capacity secondary storage and more
  • They host, like workstations, network servers and
    operating systems
  • They avoid duplicate installation of applications
    and all users will access to a common copy of the

A server is a computer connected to a network
that distributes and stores resources for other
network users.
  • Servers typically support computer networks,
    enabling users to share files,
  • software, peripheral devices, and other
    network resources.
  • Servers have large amounts of primary and
    secondary storage and powerful
  • CPUs.
  • Organizations with heavy e-commerce requirements
    and very large Web sites are
  • running their Web and e-commerce applications
    on multiple servers in server
  • farms.

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Personal Information Manager (PIM)
  • Usually, such devices would use a micro version
    of a desktop operating system, such as Pocket PC,
    Symbian, or Palm OS.
  • In general, mobile devices have the following
  • They cost much less than PCs.
  • Their operating systems are simpler than those
    on a desktop PC.
  • They provide good performance at specific tasks
    but do not
  • replace the full functions of a PC.
  • They provide both computer and/or
    communications features.
  • They offer a Web portal that is viewable on a

  • Summary
  • Supercomputers are highly sophisticated computers
    used for very special tasks like scientific
    researches etc.
  • Mainframes are large and expensive and are
    designed to meet the needs of a large
  • . Minicomputers are in between mainframes and
  • They are also called midrange computers
  • Microcomputer is also called Personal Computer
    are used by an Individuals
  • The computers around us, like - microwave ovens,
    washing machines, automobiles etc. are embedded
    computers which are special purpose and are
    generally used to perform control functions.

Operating Systems
An operating system is a collection of software
that coordinates the working of the different
components of the system and gets the users job
done. The operating system provides the user with
all the basic things necessary to do his job.
An Operating System (OS) is the master controller
within a computer. An operating system interacts
with All hardware installed in or connected to a
computer system. All software installed or
running from a storage device on a computer
system. EX Windows, MacOS, DOS, UNIX, Linux
  • The basic functions of an OS are
  • Process Management Managing the programs that
    are running.
  • Memory Management Managing and rationing the
    memory between processes and data.
  • Storage Management Managing the permanent
    Storage of data on disks or other media
  • I/O Management Managing the input and output
  • Device / Resource Management Managing devices
    and resources and allowing the users to share the
  • Security and Protection Securing the system
    against possible unauthorized access to data or
    any other entity. Protecting the parts of the
    system against damage.
  • Booting the System and getting it ready to work.
  • Data communications Providing interface to
    connect to other computers or allowing others to

Computer Viruses
  • A computer virus is a computer program that can
    copy itself and infect a computer without
    permission or knowledge of the user.
  • Virus show us loopholes in software
  • With the increasing use of the Internet, it has
    become easier for virus to spread
  • Most virus are targeted at the MS Windows OS

  • First virus was created to show loopholes in
  • 1981 Apple Viruses 1, 2, and 3 are some of the
    first viruses "in the wild" or public domain.
    Found on the Apple II operating system, the
    viruses spread through Texas AM via pirated
    computer games.
  • In March 1988, the first anti-virus software was
    written. It was designed to detect and remove the
    Brain virus and immunized disks against Brain
  • There are estimated 65,336 computer viruses in

Symptoms of Virus Attack
  • Computer runs slower then usual
  • Computer no longer boots up
  • Screen sometimes flicker
  • PC speaker beeps periodically
  • System crashes for no reason
  • Files/directories sometimes disappear
  • Denial of Service (DoS)

Virus Languages
  • C/C
  • Pascal
  • VBasic
  • Unix Shell Scripts
  • JavaScript

  • Boot Sector infectors
  • File infectors
  • Multipartite viruses
  • Macro viruses
  • Scripting viruses
  • Other ( Trojan Horse, Worm )

Boot Sector infectors
  • Used to be really popular, but with less people
    using floppy disks are becoming rare.
  • Hard to write i.e. coding such virus is
  • First sector on hard drive partion (first sector
    on floppy) is Master Boot record, contains info
    about the drive and the bootstrap loader.
  • If MBR can be messed up then when boot tries to
    get drive info from MBR for CMOS it wont be able
    to boot up.
  • May keep a copy of MBR around in case other
    programs need to use info (makes it easier to

File Infectors
  • File viruses infect executable files.
  • Historically havent been very successful at
  • Fast infectors try to infect as many other
    files as possible (instant gratification)
  • Sparse infectors only infect a few files at a
    time (in order to not be conspicuous)
  • Most really successful file infectors are
    classified as Worms.

Multipartite Viruses
  • Viruses that use more than one infection
  • File and Boot viruses
  • Becoming more popular with virus writers

Macro Viruses
  • Infect programming environments rather than OS es
    or files.
  • Almost any application that has its own macro
    programming environment
  • MS Office (Word, Excel, Access)
  • Visual Basic
  • Melissa was really successful macro virus
  • Usually spread as an e-mail attachment

Script Viruses
  • Usually refers to VBScript but could be any
    scripting environment as Unix Shell scripts,
    Hypercard scripts, Java script.
  • Usually sent as e-mail attachments
  • File name.doc. bat to fool user into opening

  • Worms are a subset of viruses.
  • The differ in the method of attachment rather
    than attaching to a file like a virus a worm
    copies itself across the network without
  • Infects the environment rather than specific
  • Morris Worm, WANK, CHRISTMA EXEC

Trojan Horse
  • A Trojan horse is a malicious program that is
  • the legitimate software.
  • A Trojan horse can be deliberately attached to
    otherwise useful software by a cracker, or it can
    be spread by tricking users into believing that
    it is a useful program
  • A cracker is someone who breaks into someone
    else's computer system, often on a network
    bypasses passwords or licenses in computer

Trojan Horse
  1. Erasing or overwriting data on a computer
  2. Corrupting files in a subtle way
  3. Spreading other malware, such as viruses. In this
    case the Trojan horse is called a 'dropper'.
  4. Setting up networks of individual computers in
    order to launch DDoS attacks or send Spam.
  5. Logging keystrokes to steal information such as
    passwords and credit card numbers (known as a key
  6. Installing a backdoor on a computer system

How can Computer infected
  • Websites You can be infected by visiting a rogue
    website. Internet Explorer is most often targeted
    by makers of Trojans and other pests. Even using
    a secure web browser, such as Mozilla's Firefox,
    if Java is enabled, your computer has the
    potential of receiving a Trojan horse.
  • Instant message Many get infected through files
    sent through various messengers. This is due to
    an extreme lack of security in some instant
    messengers, such of AOL's instant messenger.
  • E-mail Attachments on e-mail messages may
    contain Trojans. Trojan horses via SMTP.

Where They Live
  • Auto start FolderThe Autostart folder is located
    in C\Windows\Start Menu\Programs\startup and as
    its name suggests, automatically starts
    everything placed there.
  • Win.iniWindows system file using loadTrojan.exe
    and runTrojan.exe to execute the Trojan
  • System.iniUsing ShellExplorer.exe trojan.exe
    results in execution of every file after
  • Wininit.iniSetup-Programs use it mostly once
    run, it's being auto-deleted, which is very handy
    for trojans to restart

  • Winstart.batActing as a normal bat file trojan
    is added as _at_trojan.exe to hide its execution
    from the user
  • Autoexec.batIt's a DOS auto-starting file and
    it's used as auto-starting method like this -gt
  • Config.sysCould also be used as an auto-starting
    method for trojans
  • Explorer StartupIs an auto-starting method for
    Windows95, 98, ME, XP and if c\explorer.exe
    exists, it will be started instead of the usual
    c\Windows\Explorer.exe, which is the common path
    to the file.

What the attacker wants?
  • Credit Card Information (often used for domain
    registration, shopping with your credit card)
  • Any accounting data (E-mail passwords, Dial-Up
    passwords, Web Services passwords, etc.)
  • Email Addresses (Might be used for spamming, as
    explained above) 
  • Work Projects (Steal your presentations and work
    related papers) 
  • School or Research work (steal your papers and
    publish them with his/her name on it)

Well Known Trojans
  • AceBot is a tremendous backdoor Trojan, which was
    designed for performing a lot of different
    destructive actions.
  • The parasite detects, terminates and totally
    disables running antivirus software installed on
    the target computer.
  • AceBot also connects to the IRC network and uses
    it for giving the hacker a remote control over
    the compromised system.
  • Moreover, the Trojan is able to connect to
    various malicious servers and download other
    harmful parasites from there.

Other Trojans - Back Orifice , Cult of the
Dead Cow
A worm is self-replicating software designed to
spread through the network Typically, exploit
security flaws in widely used services. Can
cause enormous damage Launch DDOS attacks,
install through networks Access sensitive
information corrupt it
  • Spread over network connection
  • Worms replicate
  • First worm released on the Internet was called
    Morris worm, it was released on Nov 2, 1988.

Rules for preventing viruses
  • Keep operating system and all software
  • Use a virus scanner. McAffee and Norton are the
    two most widely accepted and used virus scanners.
  • If you are not sure about an attachment, dont
    open it.
  • You might even exchange a code word with friends
    and colleagues. Tell them that if they wish to
    send you an attachment, to put the code word in
    the title of the message. Without seeing the code
    word, you will not open any attachment.
  • Dont believe security alerts that you are
    sent. Microsoft does not send out things in this
    manner. Go check the Microsoft website regularly,
    as well as one of the anti-virus websites
    previously mentioned.

Applications of Computer
  • At Home
  • Mostly to check mails
  • Small documentation
  • Gaming
  • Music and Video
  • To solve homework
  • Photo Printouts using Good Printers
  • Work from Home concept

  • In Education
  • Schools to Universities
  • To Educate necessary skills demanded by
  • To give a demo or training
  • Server the purpose of Teaching Aids
  • To convey messages using Internet

  • In Science
  • To analyze large data acquired over a period of
  • To do complex floating point arithmetic
  • Image Processing
  • Research

  • In Industry
  • To develop software, mostly to automate the
    manual work
  • To provide necessary solution to clients needs
  • Software is developed for the needs of
    networking, banking, business, retail etc

  • Entertainment
  • Music Industry
  • Games
  • Movies to watch and create 200 Linux Machines
    in parallel to create visualization in Titanic,
    the movie
  • III Cartoons, special effects
  • Nowadays to promote theirs productions

  • Banking
  • To store, access and modify huge amounts of data
  • Online business called e-business is becoming
    popular with a small amount of limitations
  • Paying bills become easy and time saving
  • online promotions

  • Government
  • Biometrics Attendance Monitoring
  • Weather Forecasting and military applications
  • E- governance
  • Online payment of taxes, Insurances
  • Send Messages to virtually unreachable places at
  • Wireless communication

Buying a Computer
Step 1 - Processor
  • Processor (also known as CPU)
  • The clock speed of the processor measured in Mhz
    and now Ghz determines how fast the computer
    can operate.
  • In general the faster you can buy the better
  • Some Different Processors
  • Intel Pentium (IV) and Celeron
  • AMD Athlon, K-6 and Duron
  • Via Technologies MII and Cyrix

Buying a Computer
Step 2 - RAM
  • RAM Random Access Memory
  • The memory the computer uses while operating
  • In general the more RAM the more programs the
    computer can run simultaneously
  • Computers will generally come with between 512MB
  • 4 GB
  • DRAM Current Standard
  • SDRAM (Synchronous DRAM) Faster
  • (Set to work with computer clock speed)
  • RDRAM (Rambus DRAM) Even Faster

Buying a Computer
Step 3 Hard Drive Space
  • Hard Drive Memory
  • The computers long term memory
  • The place where computer programs are stored
    as well as the documents, images, sound files
    you create.
  • Desktop computers will generally come with 20GB
  • 500GB of hard drive space.

Buying a Computer
Step 4 - Monitor
15 Monitor 13.8 Viewable 17 Monitor 15.9
  • Monitor
  • General sizes 15, 17, 19, 20-25
  • 15 Standard on low priced computers
  • Viewable area measured corner to corner
  • 17 has viewable area generally 33 bigger than
  • Bigger the monitor the more space it takes up
    and the more it costs
  • Most computers use Cathode Ray Tube (CRT) like
  • Now days Flat Screen (CRT) and Flat Panel (LCD)
  • models of monitors are available in market
  • Flat Panel monitors i.e . TFT monitors are
  • small in size

Buying a Computer
Step 5 CD, CD-R,CD-RW, DVD
CD Plays CD music and installs programs from
CD CD-R Plays CD music, installs programs from
CD, and allows you to record (burn) your
own CD CD-RW Plays CD music, installs programs
from CD, and allows you to record and
re-record CDs DVD Plays CD music, install
programs from CD, and Play DVD Note DVDs will
eventually totally replace CDs
Recordable DVD is here but very expensive

Buying a Computer
Step 6 Printers
  • Printers are generally Inkjet or Laser types
  • Unless you run a small business get an inkjet
  • Ink costs are your greatest enemy

Buying a Computer
Step 7 Can you Upgrade?
  • Upgrade the Processor?
  • Memory Sockets
  • Expansion slots
  • Ports
  • Expansion Bays
  • Hard Drive or Storage

Buying a Computer
Step 8 Internet Service and Modems
  • Your computer will either need a modem or
    network card
  • to connect to the Internet
  • Modems are most common and use your phone line
    to connect
  • Modems are standard equipment and most
    computers will come with a V90 56K modem
  • Network cards are used to connect to cable
    systems and LANs
  • Many computers will come with a year free
  • Some come with rebates for signing up for long
    term service

Buying a Computer
  • SoftwareProgramsApplications (Generally)
  • Most computers will come prepackaged with enough
  • software to get you started
  • In general youll get
  • An Operating System (OS) Windows 95/98/ME/XP
  • An Application Suite such Microsoft Works
    Word Processor, Spreadsheet, Database
  • Internet Connection Software
  • Some basic games

Buying a Computer
Where to Buy?
  • Computer Superstores Perhaps best shopping
    fairly knowledgeable staff Decent Service
    beware of long term warranties
  • Electronics Superstores The person who sold
    stereos yesterday might be selling computers
    today beware of long term warranties
  • Home-Office Superstores Usually smaller higher
    end computers salespeople not experts
  • Warehouse Clubs Generally cheap, non-brand
    name computers
  • Mass Merchandisers like Kmart and Walmart
  • lower end machines
  • Catalog or Online Retailers Best prices but
    might have to
  • mail the computer in for service
  • Local Computer Stores Can be good for service,
    but watch out for mixed components

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