A mesh topology is a computer network in which every node has a dedicated point-to-point connection to every other node in the network. A mesh topology has n*(n-1)/2 routes that connect 'n' devices in the network. Mesh topology work on the concept of routes. Message that is to be delivered to the destination can take any possible shortest and easiest routes that it can find.

Mesh Topology

Advantages of Mesh topology

• As it has multiple routes between the source and the destination, if one route fails, there would be a number of other routes through which data transfer can take place.
• Traffic problem is minimized in this topology.
• Troubleshooting is easier compared to other networks like star and ring.
• Heavy load of data transfer has little impact on the performance of this topology.
• This network can be easily expanded without affecting the existing users.

Disadvantages of Mesh topology

• It is expensive as it requires more cable than other topologies.
• Installation is difficult and complicated.

A network topology refers to the interconnection of various nodes of a computer network. In other words, it defines the layout of the various devices that are part of the computer network.Topology is the virtual "shape" of the network, but it may not actually represent the actual physical design of the network that the various devices are connected to each other.
There are two types of network topologies: physical and logical.

A physical topology refers to the physical design of the computer network that includes the computers and other devices, their location and the various cables installed in the network.

A logical topology means the mode of flow of data in the network in contrast to its physical arrangement.

There are mainly six types of network topologies listed as under:

• bus
• star
• ring
• tree
• mesh
• hybrid

MAN (Metropolitan Area Network)
A MAN is a computer network that covers a geographical area that is larger than a LAN but smaller than a WAN,extending typically over a city. It is usually owned by a single entity like a government branch or a large organization.

CAN ( Campus Area Network)
A CAN is a computer network that spans multiple LANs but which is smaller than a MAN. It is mostly present in universities or a campus.

 SAN (Storage Area Network)
This type of computer network is used to connect the servers to the data storage devices for storing the data or accessing the data that was stored previously on the device.

VPN (Virtual Private Network)
A VPN is a network of computers in which some of the links between the various nodes have open connections or have virtual circuits of some larger network, typically the internet, rather than joining them with physical wires. In other words, a VPN uses the connections of the internet or some other intranet to form a private network, without actual physical connection among the devices that form the node. This allows secure communications through the internet, because the VPN can be made accessible only by authorised personnels.

PAN (Personal Area Network)
A personal area network is a network of computers and/or other devices like PDAs (Personal Digital Assistant), cell phones, telephones, fax, printers, scanners etc. This network can be used to transfer files, emails, calender appointments, digital photos, music, etc. A PAN may be constructed through wire or wirelessly, and it typically covers an area of about 10 meters.

On the basis of the area a network covers, it can be divided into the following types:

    *  LAN      -  Local Area Network
    *  WLAN  - Wireless Local Area Network
    *  MAN     - Metropolitan Area Network
    *  WAN     - Wide Area Network
    * SAN       -  Storage Area Network, System Area Network, Server Area Network, Small Area Network

    * CAN      - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
    * PAN      - Personal Area Network
    * DAN      - Desk Area Network


The original categories of computer networks were only LAN, MAN and WAN. The other categories evolved during the advancements in the technology of computer networks.

LAN (Local Area Network)

A LAN is a network of computers and devices over a relatively short geographical area. An office building networked with computers,a school or college or a home usually contains a single LAN, though sometimes one building will contain a few small LANs (probably one per room), and occasionally a LAN will span a group of nearby buildings. In addition to operating in a limited space, LANs are also controlled by a single person or organization. A LAN also tend to use certain connectivity technologies, primarily Ethernet or Token Ring.

 WAN - Wide Area Network
A WAN  spans a large physical distance compared to a LAN. The internet is the largest and the most common example of a WAN, that spans the whole Earth. A WAN can be considered as a collection of several LANs that are dispersed throughout the whole world. The network device Router connects several LANs to form the WAN. The Router also maintains both a LAN address and a WAN address in IP networking.

WLAN  - Wireless Local Area Network
WLAN is also a type of LAN(local area network) based on wireless network technology mostly referred as Wi-Fi. In contrast to a LAN, in WLAN no wires are used; radio signals are the medium for communication. To access any wireless network around, wireless network cards must be installed in the system. The wireless cards are connected to the Wireless Routers for the purpose of communication among the computers.

A computer network is a combination of computers and other computer related devices connected by communications channels for the purpose of sharing files and resources among the users. The network may be of many types, with unique features of its own.
The primary objective of computer network is to share the files among various users. Among the various networks of computers, the internet is definitely the most important inventions of modern age. It is a huge source of information on any topic, it brought the era of emails and point to point communication through voice and video, allowing anyone to communicate with anyone else in the world; and it is also a great medium of new kind of business - the online business. Everyone in the world today depend so much on the computer networks and specially the internet, that it has become a part of our daily life.

fig: Computer Networks

Hacking a computer or a website are similar in terms of the security. The fundamental skill required for this purpose is programming, be it in any language. Learning a programming language is essential to learn the hacking procedures. It is easier to learn hacking if you have open source softwares like Unix. Along with the programming skills, some knowledge about the World Wide Web and HTML (Hyper Text Markup Language - the language of the web) is necessary. Good knowledge of English language is also a plus point. But only a lot of practice on programming and HTML will make one a successful hacker.

The real question is not whether machines think but whether men do.
-B. F. Skinner, Contingencies of Reinforcement

The robot is going to lose. Not by much. But when the final score is tallied, flesh and blood is going to beat the damn monster.
-Adam Smith

I have always wished for a computer that would be as easy to use as my telephone. My wish came true. I no longer know how to use my telephone.
-Bjarne Stroustrup

If you don't know how to do something, you don't know how to do it with a computer.
-Source Unknown

Computers in the future will weigh no more than 1.5 tons. Quoted in Popular Mechanics 1950
-Source Unknown

Anyway, there's plenty of room for doubt. It might seem easy enough, but computer language design is just like a stroll in the park....
Jurassic Park, that is.
-Larry Wall

I think there is a world market for maybe five computers.
-Thomas J. Watson

If builders built buildings the way programmers wrote programs, then the first woodpecker that came along would destroy civilization.
-Harry Weinberger

As far as we know, our computer has never had an undetected error.
-Weisert

I'm not against machines, as are some people who feel that the computer is leading us back into the jungle...I'm against machines only when the convenience they afford to some people is regarded as more important than the inconvenience they cause to all.
In short, I don't think computers should wear the pants or make the decisions. They are deficient in humor, they are not intuitive, and they are not aware of the imponderables. The men who feed them seem to believe that everything is made out of ponderables, which isn't the case. I read a poem once that a computer had written, but didn't care much for it. It seemed to me I could write a better one myself, if I were to put my mind to it.
-E.B. (Elwyn Brooks) White, Dear Mr. ___, "The New Yorker", 1967

Never trust a computer you can't throw out a window.
-Steve Wozniak

A computer once beat me at chess, but it was no match for me at kick boxing.
-Emo Philips

Bill Gates is the pope of the personal computer industry. He decides who's going to build.
-Larry Ellison

Computer science is no more about computers than astronomy is about telescopes.
-Edsger Dijkstra

Computers are magnificent tools for the realization of our dreams, but no machine can replace the human spark of spirit, compassion, love, and understanding.
-Louis Gerstner

Computers are useless. They can only give you answers.
~Pablo Picasso

Computers make it easier to do a lot of things, but most of the things they make it easier to do don't need to be done.
~Andy Rooney

Computing is not about computers any more. It is about living.
~Nicholas Negroponte

Data is not information, information is not knowledge, knowledge is not understanding, understanding is not wisdom.
~Clifford Stoll

Home computers are being called upon to perform many new functions, including the consumption of homework formerly eaten by the dog.
~Doug Larson

I am not the only person who uses his computer mainly for the purpose of diddling with his computer.
~Dave Barry

I do not fear computers. I fear the lack of them.
~Isaac Asimov

I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image.
~Stephen Hawking

I think it's fair to say that personal computers have become the most empowering tool we've ever created. They're tools of communication, they're tools of creativity, and they can be shaped by their user.
~Bill Gates

Never trust a computer you can't throw out a window.
~Steve Wozniak

Part of the inhumanity of the computer is that, once it is competently programmed and working smoothly, it is completely honest.
~Isaac Asimov

People think computers will keep them from making mistakes. They're wrong. With computers you make mistakes faster.
~Adam Osborne

Supercomputers will achieve one human brain capacity by 2010, and personal computers will do so by about 2020.
~Ray Kurzweil

The computer is a moron.
~Peter Drucker

The digital revolution is far more significant than the invention of writing or even of printing.
~Douglas Engelbart

The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do.
~Ted Nelson

The idea that Bill Gates has appeared like a knight in shining armor to lead all customers out of a mire of technological chaos neatly ignores the fact that it was he who, by peddling second- rate technology, led them into it in the first place.
-Douglas Adams

At the present time there exist problems beyond our ability to solve, not because of theoretical difficulties, but because of insufficient means of mechanical computation.
-Howard Aiken, Proposed Automatic Calculating Machine, 1937

The desire to economize time and mental effort in arithmetical computations, and to eliminate human liability to error is probably as old as the science of arithmetic itself.
-Howard Aiken

Part of the inhumanity of the computer is that, once it is competently programmed and working smoothly, it is completely honest.
-Isaac Asimov

I do not fear computers. I fear lack of them.
-Isaac Asimov

One of the most feared expressions in modern times is The computer is down
-Norman Augustine

Electronic aids, particularly domestic computers, will help the inner migration, the opting out of reality. Reality is no longer going to be the stuff out there, but the stuff inside your head. It's going to be commercial and nasty at the same time.
-J. G. Ballard

I am not the only person who uses his computer mainly for the purpose of diddling with his computer.
-Dave Barry

The word user is the word used by the computer professional when they mean idiot.
-Dave Barry

The sad thing about artificial intelligence is that it lacks artifice and therefore intelligence.
-Jean Baudrillard

Computer science only indicates the retrospective omnipotence of our technologies. In other words, an infinite capacity to process data (but only data -- i.e. the already given) and in no sense a new vision. With that science, we are entering an era of exhaustivity, which is also an era of exhaustion.
-Jean Baudrillard

The most likely way for the world to be destroyed, most experts agree, is by accident. That's where we come in; we're computer professionals. We cause accidents.
-Nathaniel Borenstein

Silicon Valley is like a person running around in front of a steamroller. You can outrun the steamroller on any given day. But if you ever sit down you get squashed.
-Bob Boschert

Reading computer manuals without the hardware is a frustrating as reading sex manuals without the software.
-Arthur C. Clarke

There is never finality in the display terminal's screen, but an irresponsible whimsicality, as words, sentences, and paragraphs are negated at the touch of a key. The significance of the past, as expressed in the manuscript by a deleted word or an inserted correction, is annulled in idle gusts of electronic massacre.
-Alexander Cockburn

If the automobile had followed the same development cycle as the computer, a Rolls-Royce would today cost $100, get one million miles to the gallon, and explode once a year, killing everyone inside.
-Robert X Cringely

It is hardly surprising that children should enthusiastically start their education at an early age with the Absolute Knowledge of computer science; while they are unable to read, for reading demands making judgments at every line. Conversation is almost dead, and soon so too will be those who knew how to speak.
-Guy Debord

The best way to accelerate a Macintosh is at 9.8m/sec/sec.
-Marcus Dolengo

The computer is a moron.
-Peter Drucker

A computer won't clean up the errors in your manual of procedures.
-Sheila M. Eby

The workers and professionals of the world will soon be divided into two distinct groups. Those who will control computers and those who will be controlled by computers. It would be best for you to be in the former group.
-Lewis D. Eigen

I really don't care that I don't have what's current because whatever is at the moment, it will be infinitely better in a few months and even better months later.
-William Fink

The great thing about a computer notebook is that no matter how much you stuff into it, it doesn't get bigger or heavier.
-Bill Gates

I don't think there's anything unique about human intellience. All the nuerons in the brain that make up perceptions and emotions operate in a binary fashion.
-Bill Gates

The real danger is not that computers will begin to think like men, but that men will begin to think like computers.
-Sydney J. Harris

Life was simple before World War II. After that, we had systems.
-Grace Murray Hopper

We're flooding people with information. We need to feed it through a processor. A human must turn information into intelligence or knowledge. We've tended to forget that no computer will ever ask a new question.
-Grace Murray Hopper

I only know one person who was able to write a program in ink and have it run the first time. That was Dick Bloch. He drove nearly all of us crazy because he could do that. Since the Mark I was a relay and step counter machine, it was not too difficult to change the circuits. Every once in a while, Dick would get the idea of a new circuit that would make his problem run faster. He'd get together with one of the operators during the night and they would fix the circuit. The next morning my programs wouldn't run. It's much better to have machines that the programers cannot alter.
Commander Aiken was a tough taskmaster. I was sitting at my desk one day, and he said, You're going to write a book. I said, I can't write a book. He said, You're in the Navy now. And so I wrote a book. I have it here with me. This is the Mark I manual.
Howard Aiken always said that one day we would have computers that would fit in a shoe box. I don't t know how he knew that, but he did.
-Grace Murray Hopper

Man is a slow, sloppy and brilliant thinker; the machine is fast, accurate and stupid.
-William M. Kelly

Man is still the most extraordinary computer of all.
-John Fitzgerald Kennedy

A distributed system is one in which the failure of a computer you didn't even know existed can render your own computer unusable.
-Leslie Lamport

I have a spelling checker
It came with my PC;
It plainly marks four my revue
Mistakes I cannot sea.
I've run this poem threw it,
I'm sure your pleased too no,
Its letter perfect in its weigh,
My checker tolled me sew.
-Janet Minor

I see no reason why anyone would want a computer in their home.
-Kenneth Olsen

Hardware: the parts of a computer that can be kicked.
-Jeff Pesis

Computers are useless. They can only give you answers.
-Pablo Picasso

The most overlooked advantage to owning a computer is that if they foul up, there's no law against whacking them around a little.
-Porterfield

A computer lets you make more mistakes faster than any invention in human history - with the possible exceptions of handguns and tequila.
-Mitch Ratliffe
There will still be things that machines cannot do. They will not produce great art or great literature or great philosophy; they will not be able to discover the secret springs of happiness in the human heart; they will know nothing of love and friendship.
-Bertrand Russell

"I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image."
-Stephen Hawking.

A computer virus is only a program, similar to other computer programs. The only difference is that it is destructive. Stephen Hawking has said rightly that computer viruses should count as life. It clearly resembles the destructive aspect of human nature.

A computer virus is a computer program that can copy itself, and infect other computers. Other "destructive" computer programs like malware, spyware, adware, etc are also counted as viruses, but they are different, technically, from actual viruses. Many viruses have become famous in the past, by wreaking havoc in the field of computer industry. The viruses like Melissa virus in 1999, I Love You virus in 2000, Mydoom worm in 2004,Storm worm in 2007 etc have been famous for their destructive behavior.

What is a Virus?
A virus is a small piece of software that hides inside other software. For example, the virus may attach to a word document and spread itself to other files or programs when that document is accessed, and wreak havoc.






Types of virus

E-mail viruses
An E-mail virus travels through the e-mail messages, and replicates itself over by automatically mailing itself to the people in the victim's e-mail address book.

Trojan horses
A trojan horse is simply a computer program that claims to do one thing (it may claim to be a game) but instead does other things like damage some hardware or delete the files on the hard disk. They do not replicate automatically.

Worms
A worm is a small piece of software that uses computer networks and security holes to replicate itself. A copy of it scans the network for other security limits, and when it finds one, it copies itself to the new machine and starts replicating from that machine as well.


Computer viruses are so called because they share some of the traits of the biological virus. They pass from one computer to another, infecting each one, as the biological virus does. There are very few reasons for the existence of such virus. The first reason is the same psychology that drives the vandals and arsonists. Someone who likes to break a window on someone's house, paint signs (usually vulgar signs) on walls and buildings or burn down a beautiful forest seems to be a psychological thrill. Such persons enjoy doing damage. And computer virus is a very safe means of damaging other people's properties or whatsoever.

The second reason builds up from the pleasure of watching things blow up. Most people enjoy watching skyrockets. They are also fascinated with things like explosions and car wrecks, the reason why most movies nowadays have such scenes. Creating a computer virus is similar to that, and its a little different kind of explosion that more people would love to watch.

The next reason involves bragging rights, or the thrill of doing it. If one finds a new thing, like a big ancient tree that no one else has ever seen, he can "tell" about the tree to other people, or he can "show" them, to be the first to discover that tree. The computer virus is a means of showing that security hole in the computer system that no one else has detected before.

Recovery from viruses

Anti-virus software

An anti-virus software, as the name implies, works against the viruses - it helps to prevent the infection of the computer from the viruses, and if the computer is already infected, it helps to heal the computer by removing the virus, or in some cases, removing the infected file itself.
An anti-virus works mainly in two ways. The first and the most common method of detecting the virus is using a list of virus signature definitions. This works by comparing the contents of the computer's memory (RAM and boot sectors), and the files stored on fixed or removable drives against the database of known "virus signatures".

The second method is using heuristic algorithm to detect the viruses on the basis of the common behaviors that most of the viruses exhibit.

System restore

The system restore is a built-in feature of all windows family. It restores the registry settings and other critical system files and settings to a previous pre-set checkpoint. The checkpoint may be created by the system itself, during installation of hardwares and softwares, or it may be created manually by the user. But the defect of this method is that the files to restore the system are also saved on the hard disk itself, which may as well be infected by the virus.

Operating system re-install

Re-installing the operating system itself is another efficient method of virus removal, because while doing so, all the previous files stored on the hard disk on the partition where the operating system was, are deleted. But care must be taken in re-installing the operating system, because the new OS installation files may already be infected with viruses, and in addition to the system partition, other partitions of the hard disk may also be infected with the virus.

Computer has been the most important invention of man, yet. It differs largely from other inventions that have been changing human lifestyles. Started with simple calculations, this masterpiece of the human civilization has been serving the humans since a long time. From its large mainframe predecessors to the modern age laptops, computers have been an integral part of human life.

The history of computer has a large variation, in terms of size, shape, power consumption and operating capabilities. Early computers needed a separate room for their installation. They were too expensive to be used by the general public. But their demand in the computing areas forced them to be small, cheap and flexible.

A simple computer

A lot of terms are used to describe the computers, most of which imply the size, expected use or capability of the computer. The term computer can apply to any device that has a microprocessor in it, but in view of a general public, a computer is an electronic device that receives input from the user through a mouse or keyboard, processes it in some way and displays the result on the screen.