Introdution Of Computers

In this Chapter you will learn about
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 System5/10/2016 Saurabh Tiwari 2

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
5/10/2016 Saurabh Tiwari 3

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.

Computer System is composed of the following components &
each of the components plays an important role in computing.
Input devices
Output devices
Central processing unit (CPU) – (ALU, CU, Memory Unit)

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
Digitizer

Commonly Used Output Devices
Monitors ( Cathode ray Tube (CRT), LCD, TFT )
Printers ( Dot Matrix, Inkjet, Laser Printers)
Plotters
Screen Image Projectors
Voice Response System

Output Devices
Laser Printer

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

AMD Athlon XP 2200 +

Intel Pentium 4 2.533 Ghz Socket 478

Inside the CPU
Control Unit
Arithmetic
and Logic
Unit (ALU)
Other
registers
Memory
Address
Register
Memory Data
Register
Main
Memory
Address bus
Data bus
Control Bus (Read / Write)
Electronic
clock
Clock pulses

The Control Unit
It manages fetch, decode and
execute program instructions.
It synchronises the whole system by telling devices what to do and
when to do it
The CU sends signals to other parts of the
computer

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
programmers

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 bus—analogous to the width of a highway—determines 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 computer’s 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).

Storage Devices

38
Hardware is one that is tangible.
The storage devices (Hard disk, CD’s etc.,), mouse,
keyboard CPU and display devices (Monitor) are
Hardware.
Computer 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 Software

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,
Interpreter

Utility Software :- is the a specific tools that are used while
developing a program or package

Session - II

In this Session we are going to cover following -
1.Classification of Computer
2.Overview of Operating System
- Basic functions Operating System
3.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 Computer5/10/2016 Saurabh Tiwari 46

Type of
computer
Digital
computer
Micro
Computer
Home PC
Main frame
Computer
Super
Computer
Mini
Computer
Analog
computer
Hybrid
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 processing
 Output is continuous but obtain when computation is
completed.

NOTE BOOK COMPUTERS

PERSONAL COMPUTERS

Workstations
• 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.

WORKSTATIONS
A stand-alone computer is called a workstation on a network

Mainframes
• 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

MAINFRAMES COMPUTERS
In Past Mainframes were huge computers that could fill an entire room. It was
built by IBM in1950’s
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.

MAINFRAMES COMPUTERS

Supercomputers
• Used in scientific and engineering applications
those handling huge data and do a great
amount of computation.
• Extremely fast in operation (@ 1 trillion
operations/second)
• 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

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 $ 5Million.
decrease.
Super computers consumes the light of about100 homes.
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)

Servers
• A server is one for which many PCs are
connected.
• It has large capacity secondary storage and
more memory
• 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 program

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 ar
running their Web and e-commerce applications on multiple servers in server
farms.
SERVERS
A server is a computer connected to a network that distributes and stores resources
for other network users.

HANDHELD COMPUTERS
Personal Information Manager (PIM)

69
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 characteristics:
• 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 screen.

Summary
1. Supercomputers are highly sophisticated computers used for very special
tasks like scientific researches etc.
2. Mainframes are large and expensive and are designed to meet the needs of
a large organizations.
3. . Minicomputers are in between mainframes and Microcomputers.
They are also called midrange computers
1. Microcomputer is also called Personal Computer are used by an Individuals
2. 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 user’s 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 –
1. Process Management – Managing the programs that are running.
2. Memory Management – Managing and rationing the memory
between processes and data.
3. Storage Management – Managing the permanent Storage of data on
disks or other media
4. I/O Management – Managing the input and output
5. Device / Resource Management – Managing devices and resources
and allowing the users to share the resources
6. Security and Protection – Securing the system against possible
unauthorized access to data or any other entity. Protecting the parts of
the system against damage.
7. Booting the System and getting it ready to work.
8. Data communications – Providing interface to connect to other
computers or allowing others to connect

• 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
Computer Viruses

Background
 First virus was created to show loopholes in software
• 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 A&M
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 infection.
 There are estimated 65,336 computer viruses in existence

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
• ANSI COBOL
• C/C++
• Pascal
• VBasic
• Unix Shell Scripts
• JavaScript

Classifications:
• 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 difficult.
• 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 won’t be able to boot up.
• May keep a copy of MBR around in case other programs need to
use info (makes it easier to disinfect)

File Infectors
• File viruses infect executable files.
• Historically haven’t been very successful at spreading.
• 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
mechanism
– 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 it’s 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 it

Worms
• 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 attachment.
• Infects the environment rather than specific
objects
• Morris Worm, WANK, CHRISTMA EXEC

Trojan Horse
 A Trojan horse is a malicious program that is masked
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 programs

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 logger)
6. Installing a backdoor on a computer system
Trojan Horse

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 Folder
The Autostart folder is located in C:WindowsStart
MenuProgramsstartup and as its name suggests, automatically starts
everything placed there.
• Win.ini
Windows system file using load=Trojan.exe and run=Trojan.exe to
execute the Trojan
• System.ini
Using Shell=Explorer.exe trojan.exe results in execution of every file after
Explorer.exe
• Wininit.ini
Setup-Programs use it mostly; once run, it's being auto-deleted, which is
very handy for trojans to restart

• Winstart.bat
Acting as a normal bat file trojan is added as @trojan.exe to hide its
execution from the user
• Autoexec.bat
It's a DOS auto-starting file and it's used as auto-starting method like
this -> c:Trojan.exe
• Config.sys
Could also be used as an auto-starting method for trojans
• Explorer Startup
Is an auto-starting method for Windows95, 98, ME, XP and if
c:explorer.exe exists, it will be started instead of the usual
c:WindowsExplorer.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)

• 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.
Well Known Trojans
Other Trojans: -
Back Orifice , Cult of the Dead Cow

Worms
• Spread over network connection
• Worms replicate
• First worm released on the Internet was called Morris
worm, it was released on Nov 2, 1988.
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

Rules for preventing viruses
1. Keep operating system and all software updated/patched
2. Use a virus scanner. McAffee and Norton are the two most widely accepted
and used virus scanners.
3. If you are not sure about an attachment, don’t open it.
4. 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.
5. Don’t 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

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

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

Applications….
• 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

Applications…..
• Entertainment
– Music Industry
– Games
– Movies – to watch and create – 200 Linux
Machines in parallel to create visualization in
Titanic, the movie
– IIICartoons, special effects
– Nowadays to promote theirs productions

Business
• 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

Applications……
• Government
– “Biometrics Attendance Monitoring”
– Weather Forecasting and military applications
– E- governance
– Online payment of taxes, Insurances
– Send Messages to virtually unreachable places at
present
– 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 to
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 computer’s 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 to
500GB of hard drive space.

Buying a Computer
Step 4 - Monitor
15” Monitor 13.8” Viewable
17” Monitor 15.9” Viewable
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 15”
• Bigger the monitor the more space it takes up and the
more it costs
• Most computers use Cathode Ray Tube (CRT) like TV
• Now days Flat Screen (CRT) and Flat Panel (LCD)
models of monitors are available in market
• Flat Panel monitors i.e . TFT monitors are newest,
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
• Modem’s are most common and use your phone line to connect
• Modem’s 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 service
• Some come with rebates for signing up for long term service

Buying a Computer
Software
Software=Programs=Applications (Generally)
Most computers will come prepackaged with enough
software to get you started
In general you’ll 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; Generally
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

Introdution Of Computers

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