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Information Technology
By
B. Jeyapragash
Assistant Librarian
Department of Library and Information Science
Information Technology
 Information Technology :
The science of
information handling, particularly by computers,
used to support the communication of knowledge
in scientific, technical, economic and social fields.
 Computers : The word computer has been
derived from the Latin word `computere', which
means to calculate. Therefore, the term computer
can logically be applied to any calculating device.
Generation of computers
 I Generation 1940-1956 : component used as Vacuum Tube and
the characters are Bulky, Consumed high power, slow, less reliable,
costly, Large cooling system.
 II Generation 1956-1963 : component used as Transistor and the
characters are Small size, consumed less power, more reliable and fast.
 III Generation1964-1971 : components are used as IC's and the
characters are Reduction in size, improved performance, better
humanmachine interaction, Multiprogramming facility.
 IV Generation1971-Present : components are used Micro processor
(SSI, MSI, LSI, VLSI)
 V Generation : Present and Beyond :Artificial Intelligence
Types and Categorization of
Computers
 Based on Data :
 Analog
 Digital
Based on Application :
 Super Computers
 Mainframe Computers
 Mini Computers
 Micro Computers
Structure of a Computer:
 The term Hardware is used to represent that
portion of a Computer, which has a physical entity,
and covers the following.
 Input > Central processor Unit (memory, Control
unit and Arithmetic Logic Unit) > Out put
Input Devices :
Input hardware devices are categorized as three types.
They are
 Keyboards
 Pointing devices
 Source data entry devices
Cont..
Pointing devices
 Mouse
 Track ball
 Pointing Stick
 Touch Pads
 Light Pens etc
Cont…
Source data entry devices
 Scanning Devices
 Sensors
 Touch Screens
 Audio input devices
 Video input devices
Output Devices
 Printers
 Monitors (Visual Display Unit (VDU)-
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

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Cathode Ray Tube (CRT),
Colour Graphics Adaptor (CGA),
Enhanced Graphics Adaptor (EGA),
Vedeo Graphics Array (VGA)
Thin Film Transistor – Liquid Crystal Display (TFT-LCD)
Multifunction Printer Technology
Microfilm and Microfiche
Sound-output devices
Video-output devices
Measurement of information:




Kilobyte (KB)
Megabyte (MB)
Gigabyte (GB)
Terabyte (TB)
-
1024 Bytes
1024 KB
1024 MB
1024 GB
Timings of Processing:
 Milliseconds
- One thousandth of a Second
 Microseconds
- One Millionth of a Second
 Nanoseconds
- One thousand Millionth of a Second
 Picoseconds
- One Million Millionth of a Second
Main Memory
 Random Access Memory (RAM) : The main memory of
the computer is made of semi conductor chips called
Random Access Memory or Read / Write memory in which
we can read or write by specifying its address. RAM is
volatile and it loses its data when power is switched off.
 Dynamic RAM (DRAM): Dynamic Random Access Memory is a
main primary storage device.
 Static RAM (SRAM): Small storage device with high-speed
versions with mini buffer storage.
 EDO RAM : Extended Data Out RAM: much quicker than above
two
 SDRAM (Static Dynamic Random Access Memory) : used latest
memory chip
Read Only Memory (ROM)
 ROM or Read Only Memory chips contain data
which may be read randomly as required, but can
not be written onto.
 ROM is non-volatile and the data in it is
permanent.
 ROM contains a set of predefined instructions,
which is hard wired to enable the booting process
of the system.
Cont…
Types:
 PROM: A Programmable Read Only Memory
 EPROM: The Erasable Programmable Read Only
Memory
 EEPROM: Electrically Erasable Programmable
ROM
STORAGE DEVICES
 Random Access or Direct Access Devices
 Diskettes
 Hard Disk Drives
 Optical Disks
 Flash Memory Cards
 Magnetic Tape
 Online Secondary Storage
Software
 System Software (operating system)
Windows
 Linux
 Unix
Single (MS DOS, PCDOS) / Multi user (windows ..)

 Application Software
 Custom software
 Libsys
 Autolib etc
 Packaged software
 word processing software
 spread-sheets programs
Cont…
 Programming Language
 High level - Programming languages – Basic, Cobol,
Fortran, Pascal, C,C++, Java (object oriented Prog lang)
 Low level (machine) – Interpreter (line to line )and
compilers (entire programme)
Transmission Media
The purpose of the transmission media is to transfer a
raw bit stream from one machine to another.
 Magnetic media
 Twisted pair (telephone)
 Baseband coaxial cable
 Broad band coaxial cable (cable tv)
 Fiber optics
 Line-of –sight transmission or microwave transmission
 Communication satellite
Cont…
 MAGNETIC /OPTICAL MEDIA : One of the most common ways to
transport data from one computer to another is to write them on to
magnetic tape/Optical media to the destination machine, and read
them back in again.
 TWISTED PAIR :
 A twisted pair consists of two insulated copper wires, typically about 1mm thick.
 The twisted form is used to reduce electrical interference to similar pairs close by
 The most common application of the twisted pair is the telephone system
 Twisted pairs can be used for either analog or digital transmission
 The technology and standards are mature and stable for voice communication.
Twisted-pair cable
Cont…
 BASEBAND COAXIL CABLE:
 A
baseband coaxial cable is used for digital
transmission.
 This supports higher bandwidths than twisted pair
 It resists EMI better than twisted pair
 BROADBAND COAXIL CABLE :
 A broadband coaxial cable is used for analog transmission
on standard cable(television cabling)
 broadband networks are using
only standard cable
television technology
 Hence the cables can be used up to 300 MHz and can run
for nearly 100 km
Cont…
Cont…
 Fiber Optics:
The center conductor of a fiber-optic cable is a fiber that consists of
highly refined glass or plastic designed to transmit light signals with
little loss.
A glass core supports a longer cabling distance, but a plastic core is
typically easier to work with.
The fiber is coated with a cladding that reflects signals back into the
fiber to reduce signal loss.
Cont…
 optical technology have made it possible to transmit data by pulses of
light
 The presence of light pulse denotes 1 bit and the absence of a pulse
denoted 0 bit.
 An optical transmission system has three components – The
transmission medium, light source and detector.
 fiber optics system can transmit data at about 1000 mbps for 1 km.
 Fiber optic cable is an extremely reliable and secret transmission
media.
 It supports very high bandwidths.
Disadvantage:
 cost
 Installation difficulty
Cont…
 LINE –OF-SIGHT TRANSMISSION OR MICRO-WAVE TRANSMISSION
 For long distance communication microwave transmission is widely used
 Parabolic antennas can be mounted on towers to send a beam to another
antenna tens of kilometers away.
 This system is widely used for both telephone and television the greater the
range with a 100 meter high tower, distance of 100 km between towers is
feasible.
Cont…
COMMUINICATION SATELLITE
 The communication satellite is a big microwave repeater in the sky.
 It contains one or more transponder each of which listens to some
portion of the spectrum, then rebroadcasts it as another frequency.
 No intervening ground facilities are required between transmission
points
NETWORK – TYPES AND
TOPOLOGES
 Network:
In the world of computers, networking is the practice of
linking two or more computing devices together for the
purpose of sharing data. Networks are built with a mix of
computer hardware and computer software
Use of Networks:
 Simultaneous access to programs and data
 Sharing of peripheral devices, such as a printer and scanner
 Streamlined personal communications
 Easier backup of data
Cont…
MAJOR TYPES OF NETWORKS
LAN
WAN
MAN
(LOCAL AREA NETWORKS)
(WIDE AREA NETWORK )
(METROPOLITAN AREA NETWORK )
LAN
 A LAN connects network devices over a relatively short
distance.
 A networked office building, school, or home usually
contains a single LAN
 sometimes one building will contain a few small LANs
(perhaps one per room), and occasionally a LAN will span a
group of nearby buildings.
 LANs are also typically owned, controlled, and managed by
a single person or organization.
Cont…
 Types of LAN:
 Client /Server
A client / server LAN consist of requesting
microcomputers, called clients or nodes and supplying
devices that provides a service called the servers.
 Peer to peer
A peer-to-peer LAN is one in which all computers on the
networks communicate directly with one another without
relying on a server.
WAN
 As the term implies, a WAN spans a large physical
distance. The Internet is the largest WAN, spanning
the Earth.
 A WAN is a geographically-dispersed collection of
LANs. A network device called a router connects LANs
to a WAN.
 In IP networking, the router maintains both a LAN
address and a WAN address.
 A WAN differs from a LAN in several important ways.
Most WANs (like the Internet) are not owned by any
one organization but rather exist under collective or
distributed ownership and management.
MAN
 MAN spanning a physical area larger than a LAN but
smaller than a WAN, such as a city.
 A MAN is typically owned an operated by a single entity
such as a government body or large corporation.
 DELNET, CALIBNET,MALIBNET..
TOPOLOGY
 Networks can be laid out in different ways. The logical
layout or shape of a network is called a topology.
 The basic topologies are
 Star Network
 Ring Network
 Bus Network
 Hybrid Network
 Point to Point and Multi drop Network
 Hierarchical topology Network or Tree Network
• Star Network
 A star network is one in which all microcomputers and other
communication devices are connected to a central server.
 Electronic messages are routed through the central hub to their
destinations.
 The central hub monitors the flow of traffic
 Advantages
– the hub prevents collision between messages
- connection is broken between any communication devices and
the
hub the rest of the network devices will continue to work
Cont…
Cont…
• Ring Network
 A ring network is one in which all microcomputer and other
communication devices are connected in continuous loop
 Electronic messages are passed around the ring until they reach
the right destination
 There is no central server
 Advantages
– The messages flow in only one direction.
- thus no danger of collisions
Cont…
• Bus Network
 All communication devices are connected to a common channel
 There is no central server
 Each communications devices transmit electronic messages to
other devices
 advantages of a bus network are that it may be organized as a
client/server or peer-to-peer network
 The disadvantages are that extra circuitry software are needed to
avoid collisions between data
Cont…
Cont…
 Tree or Hierarchical
 the root (central) node of the network is at the top of the
network
 Under the root node are branches that each span out
into other branches
Cont…
Cont…
• Hybrid Network
 Hybrid networks are combinations of star, ring and bus
networks.
Point to Point and Mulit drop Network
-Point to Point network stands for connection between
two specific points at either end of a link. (AB)
-Multidrop Network usually are divided into several
different segments with intermediary nodes. (ABCD)
Switching systems
 Switching is the device used to link the sender and
receiver in the communication channel. Three
switching systems are
 Circuit switching
 Message Switching
 Packet Switching
Cont…
 Circuit Switching :
 This techniques that directly connects the sender and
receiver in an unbroken path.
 Once connection is established and a dedicated path
exists between both ends
 Advantages:
No blocking
 No channel access delay
Disadvantages : Inefficient use of channels (when connection
device are not using) and
More expensive

Cont…
 Message Switching
 No need to establish a dedicated path between two
stations.
 Message is transmitted through the network by node to
node
 Advantage : efficiency than circuit switched and
message priorities can be established.
Cont…
 Packet Switching :
 In packet switching a message is broken into small parts
called packets.
 Each packets is tagged with appropriate source and
destination addresses
 Advantages: cost effective
 Disadvantages: minimize link efficiency
Protocols is typically more complex
packets are easily lost
Multiplexing
 Multiplexing is used to combine and transmit several
low bandwidth channels across a single high - band
width channel.
 The two basic types of multiplexing are
 Frequency-Division Multiplexing (FDM)
 Time Division Multiplexing (TDM).
Protocols
 TCP/IP : Transmission Control Protocol / Internet Protocol
(TCP/IP) is an industry standard suit of protocols providing
communication in a hydrogenous environment.
 HTTP :Hypertext Transfer Protocol provides a way for a web
browser to access a web server and request a hypermedia
documents created using HTML.
 FTP: FTP (File Transfer Protocol) is an Internet file transfer
service that operates on the Internet and over TCP/IP). FTP is
basically a client / server protocol in which a system running
the FTP server accepts commands from a system running an FTP
client.
Video Conferencing
 Video Conferencing is the use of television, video and
sound technology as well as computer technology to
enable people in different locations to see, hear and
talk with one another.
 Video conferencing can still consist of people meeting
in separate conference rooms with specially equipped
television cameras.
Bulletin Board service
 A bulletin is a communication system that allows users to





call in and either leave or retrieve messages.
This is like a single large mail box
Usenet is a global bulletin service
It is a system of distributed bulletin boards looking after
discussion groups or chat lines
Usenet is the conceptually huge bulletin board system
which allows its users to send messages on an electronic
board for anyone to see.
Eg. Federal bulletin board (keeping America informed)
Hypertext and Hypermedia
 Hypertext –
 A hypertext document is an electronic document that
contains links to related pieces of information.
 hypertext is text with pointers to other text.
Cont…
 Hyper media:
 Hypermedia is a superset of hypertext.
 Hypermedia documents contain links not only to other
pieces of text, but also to other forms of media - sounds,
images, and movies.
 Images themselves can be selected to link to sounds or
documents.
 Hypermedia simply combines hypertext and
multimedia.
Integrated Services Digital Network (ISDN)
 Integrated Services Digital Network (ISDN) is an all
digital telephone service that provides reliable voice
and data communications using the same wiring as the
existing telephone network.
 ISDN operates over standard twisted-pair wiring.
 ISDN signal is all digital
 ISDN lines provide a clean, error free connection at all
times.
Open System Interconnectivity
 In 1977, International Organization for
Standardization (ISO), composed of industry
representatives, created a subcommittee to
develop data communication standards that
promote
interoperability
and
universal
accessibility.
 The result of this effort is the Open System
Interconnection.
Cont…
Layers of the OSI Model
 Physical layer transmits bit stream to physical medium
 Data line layer provides data exchange between devices on the





same medium.
Network layer takes care of switches and routes information
units.
Transport layer provides reliable end-to-end data transmission.
Session layer maintains dialogue between communication
devices
Presentation layer formats data (ex: ASCII)
Application layer provides general services related to
applications.