Transcript HSTS104__lectures_wk1_to_wk3x

Statistical Computing 1
HSTS104
Facilitator: Albert Machisvo
[email protected]
[email protected]
Timetable: Tue 4-6pm
Wed 4-5pm
Tutorials: Mon to Wed 2-4pm
Faculty Lab in the dept of Physics
What is a computer ?
A computer is an electronic
device capable of performing
arithmetic and logical
operations. It can also store a
large volume of information.
Arithmetic operations involve the
general mathematical calculations
like addition, subtraction,
multiplication and division.
Logical operations involve
comparisions like > < = etc.
How does a computer work?
INPUT  PROCESS  OUTPUT
INPUT consists of DATA &
INSTRUCTION.
PROCESS is a set of instructions stored in
the computer to carry out the instructions
given by the user. The process is also called
a PROGRAM.
OUTPUT is the set of results generated
after processing the Input.
DATA & INFORMATION
DATA is described as some FACTS,
FIGURES and STATISTICS about a
particular instance.
For example : MARKS in individual
subjects.
INFORMATION is some FACTS, FIGURES
and STATISTICS which help us in decision
making. Generally information is the result of
data processing.
For example : PERCENTAGE & GRADE.
HARDWARE
Hardware are the PHYSICAL
COMPONENTS of the Computer System.
Examples :
All the electronic parts.
All cables.
All accessories.
SOFTWARE
SOFTWARE are the logical components of
the computer system. These are basically the
programs and information stored in the
computer.
The hardware and software can be better
explained with the help of a music system.
Hardware :
The device, cassette, tape, wires etc.
Software :
The music stored in the tapes.
Characteristics of Computer
SPEED
STORAGE
ACCURACY
VERSATILITY
AUTOMATION
DILIGENCE
SPEED
The speed with which the computer works can
be understood by the units of measurement of
time within a computer.
They are :
MILLI SECOND – 1/1000TH OF A SECOND
1 MHz = 0.001 ms(p)
STORAGE
As already discussed a computer can store a
large volume of information.
The factors to be considered for storage are :
•RETREIVAL – IMMEDIATE
•SPACE – VERY LARGE
•MEDIA – MAGNETIC MEDIA
•LONGIVITY – FOR EVER
ACCURACY
The accuracy of the computers is
consistently high. Errors in the machinery
may occur, but due to efficient errordetecting techniques, these very seldom
lead to wrong results. Errors in computing
are due to human rather than technological
weaknesses.
VERSATILITY
Computers seem capable of performing any task,
provided the task can be broken to a series of logical
steps.
The computer actually performs only four basic
operations :
•Exchanges information with the outside world via
INPUT / OUTPUT devices
•Transfers data within the computer to the different
units
•Performs basic arithmetical operations
•Performs operations of comparison
AUTOMATION
Once a program to perform a
particular task is stored in the
computer, the individual instructions
in the program are carried out one
after the other automatically to
complete the task.
.
DILIGENCE
Being a machine, a computer does not suffer
from the human traits of tiredness and lack of
concentration. If 5 million calculations are to be
performed, it will perform all of them, even the
last one with exactly the same accuracy and
speed.
In fact, there are some computers which are
constantly on for hours, days, months and years
are never switched off.
BASIC STRUCTURE
The computer receives input, processes it and
delivers output.
To perform these tasks it has different units and
each unit is responsible for a specific task.
The units are INPUT, MEMORY, CONTROL
UNIT (CU), ARITHMETIC & LOGIC UNIT
(ALU) AND OUTPUT.
The CU and ALU together are called CENTRAL
PROCESSING UNIT (CPU).
INPUT DEVICE
It is used for transferring data from the users’
end to the computer.
OUTPUT DEVICE
It is used to transfer processed information from
the computer to the user in a way required by the
user.
MEMORY UNIT
It stores instruction and data and provides them
to the various other units as and when required.
It is basically the working memory of the
computer system. This memory unit is volatile,
i.e. it is temporary memory and nothing can be
stored here permanently. The information is
stored in the main memory as long the computer
is switched on or as long as it is required by the
computer.
CONTROL UNIT
Controls the various operations
within a computer. It basically
manages all the other units and
devices of the computer system. It
does so by transmitting timing and
control signals to the various
devices and units.
ARITHMETIC & LOGIC UNIT
It performs the various arithmetic
and logical operations on the data
stored in memory, as dictated by the
instruction.
There are various basic circuits to
perform these operations.
SECONDARY STORAGE
It stores the various data, information and
programs permanently for future retrieval.
The information is organised in such a way
to retrieve it in minimum time whenever
required. The stored information remains as
long the user wants it.
BUS
These are a set of connecting wires
used for setting interconnection
between the various devices in the
system. Each set of bus has a
specific function to perform like
carrying data, carrying control
signals and addresses.
BLOCK DIAGRAM
DATA FLOW
CONTROL FLOW
SECONDARY
STORAGE
INPUT
DEVICE
MEMORY
UNIT
OUTPUT
DEVICE
CONTROL
UNIT
ARITHMETIC
& LOGIC UNIT
CPU
DATA REPRESENTATION WITHIN A
COMPUTER
CHARACTER :
A character is the smallest amount of
information that can be communicated to the
computer. All data, information and
instruction are represented by a combination
of these characters.
All alphabets, digits and symbols are
characters. Even a blank space is a
character.
How does the computer
understand a character?
Computer being an electronic
device, can represent only two states
– VOLTAGE and NO VOLTAGE.
Voltage is represented as
1
No voltage is represented as
0
There are eight such positions to represent
0 or 1 and each such position is called a
BIT. Hence the pattern generated to
represent a character is a BIT PATTERN.
BIT
1 0 1 1 1 0 0 1
UNIT FOR MEASUREMENT OF
INFORMATION
8 BIT = 1 CHARACTER = 1 BYTE
1024 BYTES = 1 KILO BYTE (KB)
1024 KB = 1 MEGA BYTE (MB)
1024 MB = 1 GIGA BYTE (GB)
1024 GB = 1 TERA BYTE (TB)
HARDWARE
Input devices :
KEYBOARD : It is an input device
to give character based inputs to
the computer. All types of data,
instruction and information can
be given through the keyboard.
MOUSE : It is used for graphics
based inputs. It can mainly select
some graphical icons and select
some options from a menu. It can
not be used for giving data to the
computer.
SCANNER : It is
used for graphical
inputs.
Pictures, images,
drawings etc. can
be scanned and
stored in the
computer.
BAR-CODE RECOGNITION :
Lines or bars can be arranged in a
code and are used particularly for
labelling goods etc. Bar-code
reading is performed by a
scanner. A sequence of bits is
generated and the information is
recorded.
BAR CODE FOR PRODUCT CODE
OUTPUT DEVICES
1. VDU : Visual Display Unit
2. Printer
PRINTER : A printer produces
output on paper which can be
permanently kept.
TYPES OF PRINTERS :
•DOT MATRIX
•INK JET PRINTER
•LASER PRINTER
DOT MATRIX
INK-JET
LASER
DOT
MATRIX
INK
JET
LASER
CHARACTER
BASED
OUTPUT
YES
YES
YES
GRAPHICS
BASED
OUTPUT
NO
GOOD
EXCELLENT
OUTPUT
QUALITY
OK
GOOD
EXCELLENT
COST
EFFECTIVE
LOW
RECURRIN
G COST
HIGH
RECURRING
COST
VERY HIGH
RECURRING
COST
COLOR
NO
OK
EXCELLENT
FLOPPY DISK
HARD DISK
CD ROM
MEMORY : There are two types of
memory : RAM & ROM.
RAM : Random Access Memory.
It is the main memory of the
computer. It is volatile memory
and the information gets erased
whenever the power supply is
switched off.
There are different types of RAM:
Static RAM (SRAM) This RAM will maintain its data
as long as power is provided to the memory chips.
It does not need to be rewritten periodically. SRAM
is very fast but much more expensive than DRAM.
SRAM is often used as cache memory due to its
speed. (CACHE memory is the memory used directly
by the CPU).
Dynamic RAM (DRAM) DRAM, unlike SRAM, must be
continually rewritten in order for it to maintain its
data. This is done by placing the memory on a
refresh circuit that rewrites the data several
hundred times per second. DRAM is used for most
system memory because it is cheap and small.
ROM : Read Only Memory
Information is burnt into the ROM chip at
the time of manufacturing. It can not be
erased or altered and fresh information
can not be written into the ROM.
The BIOS is stored on ROM because the
user cannot disrupt the information.
BIOS : Basic Input Output System.
It contains some instructions required
internally by the computer.
CPU : Central Processing Unit. It is
also called the micro processor.
There are CPUs with varying
efficiency and the quality of the
computer depends mainly on the
CPU present on the main board.
Example of some CPUs by Intel.
•8088
1985
•80386
1987
•80486
1988
•Pentium – I
1990
•Pentium – II
1994
•Pentium - III
1995
•Pentium – IV
2001
•Core 2 Duo/Centrino 2006-2008
•I3
2012
•I5
2012
•I7
2012
MOTHER BOARD : The main circuit board
housing the microprocessor, RAM, ROM
and connecting interfaces to the various
other devices and peripherals.
CABINET HOLDING THE MOTHER
BOARD AND OTHER COMPONENTS
SOFTWARE :
A set of programs that utilises
the hardware and uses its’
capabilities to perform various
tasks.
Program : A program is a set of
instructions stored in the
computer to solve specific
problems.
CLASSIFICATION OF SOFTWARE
SOFTWARE
SYSTEM
OPERATING SYSTEM
APPLICATION
TRANSLATORS
INTERPRETER
COMPILER
READY-MADE
CUSTOMISED
SYSTEM SOFTWARE :
The system s/w are a set of
programs specially designed for
performing tasks such as,
controlling the computer
hardware, and utilising the
resources to help the application
software solve specific problems.
OPERATING SYSTEM : Programs to
control the hardware and provide
user interface. It is essential for
every computer.
Functions :
•Memory management
•CPU management
•Input / Output management
•Storage / File management
•Provide user interface
TRANSLATOR : Translates high level
language to low level language and
vice-versa.
LOW LEVEL LANGUAGE : The language of
bits understood directly by the computer.
It is also called the machine language.
HIGH LEVEL LANGUAGE : The
language of users understood by
the computer only after
translation.
A computer language comprises
of key words and syntax. Using
the key words and following the
syntax, commands and
instructions are written step by
step to develop the program.
The program is then translated
into machine language by using
the translators.
There are many languages and
any one can be used to develop
programs.
Each language has it’s
capabilities and limitations.
COBOL
Commercial applications
BASIC
Beginners’ language
FORTRAN Mathematical and scientific applications
C
System level programming
APPLICATION SOFTWARE :
These are programs developed
using one of the languages to
perform a specific task.
READY MADE :
These are programs developed
by software companies for
general purpose applications.
These programs can be bought
and can be installed in the hard
disk of a computer.
Examples : MS-WORD, FACT,
TALLY, FOXPRO etc.
CUSTOMISED OR TAILOR MADE :
These are programs developed for
SPECIFIC USER REQUIREMENT
within an organisation. These
programs are developed by
programmers as per the user
requirements.
Examples : Mark-sheet, Salary, Sales
information, Railway reservation etc.
MS-DOS
Microsoft
Disk Operating System
FILE :
Related information or data is stored
in the form of a file in the disk.
Hence, the minimum chunk of
information that we can store in or
retrieve form a disk, is a file.
The files are either program files or
data files.
Each file must have a unique
name.
The file name has two parts :
PRIMARY NAME &
SECONDARY NAME or extension.
The primary name is to identify
the contents and the extension is
to identify the type of the file.
The primary file name and the
extension is joined by a period.
The extension is optional.
Legal characters in the file names include all
letters of the alphabet, numeric digits and
punctuation marks
except the following
characters :
*?=+|:[];,/\<>“
A blank space can not be used in the file name.
Capital & small letters are treated as the same.
WILD CARD :
The wild card allows us to deal
with more than one file at a time
and helps us to group the files.
*
A substitute at the beginning
? A substitute at specific positions
*.TXT
Primary name – anything
Extension - .TXT
SALARY.*
Primary name – SALARY
Extension - anything
A*.*
Primary name – starting with A
Extension - anything
*.*
BIODATA.TXT
BOOK.TXT
NOTES.TXT
SALARY.98
SALARY.DAT
SALARY.DOC
ALASKA.DOC
ABC.123
A
All files
Primary name – anything
Extension - anything
*.
Primary name – anything
Extension – nothing (must not be there)
SALARY
BIODATA
123
?A*.TXT
Primary name – second character A
Extension - .TXT
*.?O?
Primary name – anything
Extension – second character O
SALARY.TXT
DATA.TXT
RANA.TXT
SALARY.DOC
COMMAND.COM
NOTES.SOS
DRIVE NAMES
A computer can have more than
one disk drives like hard disk,
floppy disk drive & CD-rom drive.
Each of these drives are identified
by an alphabet and a colon
symbol as A:, B:, C: etc.
In order to make the computer
work, the operating system program
files must be loaded into the
memory from the disk. This process
is automatically initiated as soon as
a computer is switched on. This
process is called booting.
The booting takes place with the
help of instructions in the ROM.
Following tasks are carried out during
booting :
• Test the computer hardware
•Check all the devices
•Load the operating system files from
the disk
The computer is ready to interact
with the user only after booting is
carried out successfully.
DOS program files necessary
for booting :
IO.SYS
Responsible for the INPUT / OUTPUT operations
MSDOS.SYS
Responsible for the DISK & FILE operations
COMMAND.COM
Acts as the command interpreter to translate the user instructions.
Computer Virus
What is computer virus?
Computer virus refers to a
program which damages
computer systems and/or
destroys or erases data files
Types of Computer Virus
Time Bomb
Logical Bomb
Worm
Boot Sector Virus
Macros Virus
Script Virus
Trojan Horse
Time Bomb
A time bomb is a virus
program that performs an
activity on a particular date
Logical Bomb
A logical bomb is a destructive
program that performs an
activity when a certain action
has occurred.
Worm Virus
A worm is also a destructive
program that fills a computer
system with self-replicating
information, clogging the
system so that its operations
are slowed down or stopped
Boot Sector Virus
A boot sector virus infects
boot sector of computers.
During system boot, boot
sector virus is loaded into
main memory and destroys
data stored in hard disk
Macro Virus
A macro virus is associated with
application software like word and
excel. When opening the infected
document, macro virus is loaded
into main memory and destroys the
data stored in hard disk
Script Virus
Commonly found script viruses
are written using the Visual Basic
Scripting edition (VBS) and the
JavaScript programming
languages
Trojan Horse
Trojan Horse is a destructive
program. It usually pretends as
computer games or application
software. If executed, computer
system will be damaged.
Trojan Horse
Trojan Horse usually comes
with monitoring tools and
key loggers
Actions to prevent virus infection
Prevention by installing an
antivirus software
Always update your anti-virus
software at least weekly.
Back up your important files and
ensure that they can be restored.
Change the computer's boot
sequence to always start the PC
from its hard drive
Actions to prevent virus infection
Don't share Drive C: without a
password and without read-only
restrictions.
Empty USB drives before turning
on computers, especially laptops.
Actions to prevent virus infection
Forget opening unexpected e-mail
attachments, even if they're from
friends
Get trained on your computer's antivirus software and use it.
Have multiple backups of important
files. This lowers the chance that all
are infected.
Actions to prevent virus infection
Install security updates for your
operating system and programs as
soon as possible.
Jump at the chance to learn more
about your computer. This will
help you spot viruses.
Economic Impact of Computer Viruses
• Labor costs for analyzing and repairing
infected systems
• Loss of user productivity
• Loss of income
• Huge investments in anti-virus
technology
• Secondary costs, e.g. stealing private
info
Ethics, Rules, and Laws
Using the computer appropriately.
What are ethics
• Standards of right and wrong
behavior
• A gauge of personal integrity
• The basis of trust and cooperation in
relationships with others
What are ethics not?
• Laws that carry a criminal penalty
• Detailed instructions for every possible
situation
• Flexible and changing depending on each
unique person or situation
Where do ethics come from?
•
•
•
•
Values of a society
Values of a school, business, or organization
Values from family and heritage
Values of an individual
The ’Ten Commandments of
Computer Ethics’
1.
THOU SHALT NOT USE A COMPUTER TO HARM
OTHER PEOPLE.
2.
THOU SHALT NOT INTERFERE WITH OTHER
PEOPLE'S COMPUTER WORK.
3.
THOU SHALT NOT SNOOP AROUND IN OTHER
PEOPLE'S COMPUTER FILES.
4.
THOU SHALT NOT USE A COMPUTER TO
STEAL.
5.
THOU SHALT NOT USE A COMPUTER TO BEAR
FALSE WITNESS.
The ’Ten Commandments of
Computer Ethics’
1.
THOU SHALT NOT COPY OR USE PROPRIETARY
SOFTWARE FOR WHICH YOU HAVE NOT PAID.
2.
THOU SHALT NOT USE OTHER PEOPLE'S COMPUTER
RESOURCES WITHOUT AUTHORIZATION OR PROPER
COMPENSATION.
3.
THOU SHALT NOT APPROPRIATE OTHER PEOPLE'S
INTELLECTUAL OUTPUT.
4.
THOU SHALT THINK ABOUT THE SOCIAL CONSEQUENCES
OF THE PROGRAM YOU ARE WRITING OR THE SYSTEM
YOU ARE DESIGNING.
5.
THOU SHALT ALWAYS USE A COMPUTER IN WAYS THAT
INSURE CONSIDERATION AND RESPECT FOR YOUR
FELLOW HUMANS.
INTERNET ETHICS AND OBJECTIONABLE MATERIALS
• Three categories of objectionable
.
material
–
–
–
–
Pornographic material
Racist literature
Illegal acts
Incorrect, inappropriate, or dangerous
material
– Inaccurate information
Copyright laws.
Software developers own their programs.
Software buyers only own the right to use the
software according to the license agreement.
No copying, reselling, lending, renting, leasing, or
distributing is legal without the software owner’s
permission.
Copyright vs. Plagiarism
• Copyright
– One who violates
copyright breaks laws
that protect the rights of
the creator of an original
work
– Violation of copyright law
may results in fines,
imprisonment, or both
• Plagiarism
– One who plagiarizes
breaks a moral code by
claiming credit for the
work of someone else
– Plagiarism may result in
academic dismissal or
loss of job.
Software licenses: Four types
Public Domain
Freeware
Shareware
All Rights Reserved
Public Domain License
This software has no
owner and is not
protected by copyright
law.
It was either created
with public funds, or
the ownership was
forfeited by the creator.
•
•
•
•
Rare
Unreliable
Poor quality
Virus-laden
No cost? That may be
exactly how much this
software is worth.
Freeware License
Freeware is copyrighted
software that is licensed
to be copied and
distributed without
charge.
Freeware is free
because the license says
it is, but it’s still under
the owner’s control.
Some freeware is
“really good stuff.”
•
•
•
•
Pegasus Mail
Eudora Light
Netscape
Internet Explorer
Shareware License
The software is licensed
for copying and sharing • Some shareware trials
expire on a certain date
for a trial period, but
•
Payment
depends
on
the
payment must be made
honor system
to the owner for
• Purchasing (the right to
permanent use.
use) the software may also
get you a version with
more powerful features
and published
documentation.
All Rights Reserved License
May be used by the purchaser according the exact
details spelled out in the license agreement.
You can’t legally use it--or even possess it-- without
the owner’s permission.
Computers are available in different
shapes, sizes and weights, due to these
different shapes and sizes they perform
different sorts of jobs from one another.
They can also be classified in different
ways.
Super computer
The biggest in size, the most expensive in price than
any other is classified and known as super computer. It
can process trillions of instructions in seconds. This
computer is not used as a PC in a home neither by a
student in a college.
Governments specially use this type of computer for
their different calculations and heavy jobs. Different
industries also use this huge computer for designing
their products.
In most of the Hollywood’s movies it is used
for animation purposes. This kind of computer
is also helpful for forecasting weather reports
worldwide.
Mainframes
Another giant in computers after the super computer
is Mainframe, which can also process millions of
instruction per second and capable of accessing
billions of data.
This computer is commonly used in big hospitals, air
line reservations companies, and many other huge
companies prefer mainframe because of its capability
of retrieving data on a huge basis.
This is normally too expensive and out of reach from a
salary-based person who wants a computer for his
home.
Minicomputer
This computer is next in line but less
than mainframe in work and
performance.
These are the computers, which are
mostly preferred by the small type
of business personals, colleges, etc.
Personal computers
Almost all the computer users are familiar with the
personal computers. They normally know what the
personal computer is and what are its functions.
This is the computer mostly preferred by the office /
home users. These computers are lesser in cost than the
computers given above and also, small in size; they are
also called PCs in short for Personal computers.
This computer is small in size and you can easily arrange
it to fit in your home / office with its all accommodation.
Today this is thought to be the most popular computer in
all.
Notebook / Laptop
Having a small size and low weight the notebook is
easy to carry to anywhere. A student can take it with
him/her to his/her school in his/her bag with his/her
book.
The approach of this computer is also the same as
the Personal computer. It can store the same amount
of data and having a memory of the same size as that
of a personal computer.
Palmtop
More commonly known as Personal Digital
Assistants (PDAs), palmtops are tightly
integrated computers that often use flash
memory instead of a hard drive for storage.
These computers usually do not have keyboards
but rely on touchscreen technology for user
input.
Wearable Computers
The latest trend in computing
is wearable computers.
Essentially, common computer
applications (e-mail, database,
multimedia,
calendar/scheduler)
are
integrated into watches, cell
phones
Comparisons between different types of computers:
Type
Components
Physical
Size and
Capacity
Cost
Usage
Microcompute
r
All components
in a single unit
Smallest
Cheapest
Minicomputer
Several
functional units
Small
Cheap
Mainframe
computer
Several
separate units
Large
Expensive
Supercomput
er
Several
separate units
Largest
Most
expensive
At homes, in
schools
and
offices
In
universities,
medium-sized
companies,
departments
of
large companies
In
large
organizations,
universities,
government
In
scientific
research, weather
forecasting, space
exploration,
military defense
Network
Communication
- means to an
exchange of information between two or
more parties and it can be exchange in a
variety of way, that might be in the form of
word, letters, messages drawing, body
movement or any other symbols that
represents the idea which make to other
understandable.
Data communication :
entails electronically exchanging data
or information. It is the movement of
computer information from one point to
another by means of electrical or
optical transmission system. This
system often is called data
communication networks.
The
key
technology
of
the
information age is computer
communications.
•The
value
of
high-speed
data
communication network is that it brings
the message sender and receiver closer
together in time.
•It facilitates more efficient use of
computers and improves the day to day
control of business by providing faster
information flow.
A computer network is a system in which a
set
of
computers
and/or
other
communication facilities are connected to
each other such that they can exchange
data between themselves and other
computers on the network. It might involve
physical wire, infrared or radio frequency
communication, and can be usually used to
share files, devices and connections to other
computers. In short, a computer network
allows your computers to talk to each other.
Reasons for networking:
To allow users to communicate with
each other.
•Pass data between users without the
use of floppy disks — Files can be copied
and accessed across the network,
eliminating the time wasted and
inconvenience caused by using floppy disks
to transfer files. There is also less restriction
on the size of file that can be transferred
To share hardware.
•Share expensive peripherals, such
as printers — All of the computers
can access the same printer, modems
or CD-ROM tower.
To share software and information.
•Centralize key computer programs, such as finance and
accounting programs, word processing, time and billing —
It is often important that all users have access to the same
program (and not copies of it) so that they can work on it
simultaneously. Networking allows offices to have such a
central program that all users can access.
•Automate unattended backup of valuable — It is always
essential to keep backups of any important files. You can
automate this procedure by having a computer program that
backs up the files for you. Without a network, you would have
to manually copy files, which is time consuming.
Basic Components
of a Network
Server or host computer: A server is a
machine that provides clients with
service.
Servers share a specific
resource with other computers.
Client: A client is a computer such as a PC or a
workstation attached to the network, which is used to
access shared network resources. Client computer
uses the resources shared by server computer. The
client is the input/output hardware device at the other
end of communication circuit. It typically provides
users with access to the network and data and
software on the server. There are three major
categories of clients: terminals,
minicomputers/workstation, and special purpose
terminals.
Circuit: The circuit is the pathway through which the
message passes. Circuits can be twisted pair cable,
coaxial cable, fiber optic cable, microwave transmission,
and so forth. There are many devices in the circuit that
perform special functions, such as hubs, switches,
routers and gateways.
•Cables & Connectors – Cables carry electronic
signals from one computer to another &
Connectors attach cables to network interface
cards.
Protocol
Cable
Speed
Topology
Ethernet
Twisted Pair, Coaxial,
Fiber
10 Mbps
Linear Bus, Star,
Tree
Fast
Ethernet
Twisted Pair, Fiber
100 Mbps
Star
LocalTalk
Twisted Pair
.23 Mbps
Linear Bus or Star
Token Ring
Twisted Pair
4 Mbps - 16
Mbps
Star-Wired Ring
FDDI
Fiber
100 Mbps
Dual ring
ATM
Twisted Pair, Fiber
155-2488 Mbps
Linear Bus, Star,
Tree
LAN TOPOLOGIES :
What is a Topology?
The physical topology of a network refers to the
configuration of cables, computers, and other peripherals.
Physical topology should not be confused with logical
topology which is the method used to pass information
between workstations.
Topology
Configuration
Advantage
Disadvantage
Star
All nodes are
connected to the
central computer
Relatively
efficient;
Nodes are free to
join or quit from
the network
Dependent on the
central computer
Ring
All nodes are
connected in a
continuous loop
High speed
Whole network
will break down if
one node fails
Bus
All nodes are
connected to a
single cable and
share it
Easy to install
and cheap;
No
need
to
restart
the
network if a node
fails or joins the
Comparatively
low speed
Clients and Servers:
In general, all of the machines on the Internet
can be categorized as two types: servers and
clients.
Those machines that provide services (like Web
servers or FTP servers) to other machines are
servers. And the machines that are used to
connect to those services are clients.
IP Addresses:
To keep all of these machines straight, each
machine on the Internet is assigned a unique
address called an IP address. IP stands for
Internet protocol,
So here it is:
The Internet is made up of millions
of machines, each with a unique IP
address. Many of these machines
are server machines, meaning that
they provide services to other
machines on the Internet. You
have heard of many of these
servers: e-mail servers, Web
servers, FTP servers, Gopher
servers and Telnet servers, to
name a few. All of these are
provided by server machines.
WWW
The World Wide Web (WWW) is a collection
of host computers that deliver documents,
graphics and multi-media to users via the
Internet.
The common protocol used on the WWW is
HTTP. It stands for Hyper-text transport
protocol.
Each host computer on the World Wide
Web provides files in any format, such as a
graphics file, text document, powerpoint
presentation or audio file. Prior to the
World Wide Web, the display, searching,
and viewing of files was difficult and took a
long time.
Advantages of the WWW:
• The WWW lets users link documents together
using hyperlinks (a connection to another
document on the WWW).
 Easy linking of documents to other documents
 Documents are simple to create and make
available for other people to use
 Support for multiple multimedia components in a
single document (such as text, images, sound
and video)
 Access to anyone connected to the Internet with
a web browser
 Easy to publish and share information to other
people all around the world
Web Browser
A web browser is a software program that
interprets documents that you request from a
web server on the WWW. It displays them for
you to view. The two common types of web
browsers are Netscape Communicator and
Internet Explorer.
Web Pages
Web pages are documents stored on web
servers. The pages are written in a special
language called HTML.
Hyper-Link
A hyperlink is a link to another document or
resource. It is often shown in blue underline.
When a user clicks on a hyperlink, the client
Firewalls
A firewall is a device that protects a
network (group of computers) from
outside interference.
Computers can be damaged by people
using the Internet. A firewall protects the
computers from damage.
How do I find Information on the Internet?
There is a lot of information available on the Internet.
Some of the information is useful. A lot of the
information is not useful. It is important to find
information quickly. A lot of time can be wasted.
Useful information can be found in internet with the
help of SEARCH ENGINES.
A search engine is a web server that searches for
information on the Internet.
Search engines create a list (called a database) of
resources they find on the WWW. People ask search
engines to add their web pages to the database.
Sometimes this is free. Sometimes you have to pay
money.
Here is a list of some search engines.
www.yahoo.com
www.google.com
www.dogpile.com
www.metacrawler.com
www.altavista.com