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Concept "a Local Network"
The local network is a group of computers which can communicate with each other, in common use the peripheral equipment (for example, hard discs, printers, etc.) and to address to the removed central computers or other local networks. The local network can consist of one or more files - servers, workstations and peripheral devices. Users of a network can use in common the same files (both files of the data, and files of programs) to send messages directly between workstations and to protect files with the help of powerful system of protection. All networks (irrespective of complexity) are based on this simple principle.
The birth of computer networks has been caused by practical need - to have an opportunity for sharing the data.
The concept "the local computer network" - a LAN (Local Area Network) - concerns to geographically limited (territorial or it is industrial) to hardware - software realizations. In other words, a LAN name the group of the computers connected with each other located in some limited area. The sizes a LAN can considerably differ.
The local network can consist of two workstations located in one room, or form several hundreds the workstations scattered on different floors of an office building, and also on several buildings of area.
Local computer networks differ from other networks that they are usually limited to moderate geographical area (one room, one building, one area).
The overwhelming part of computers of the Western world is incorporated into this or that network. Operating experience of networks shows, that about 80% of all information sent on a network becomes isolated within the framework of one office.
There are two basic such as computer networks:
- networks;
- networks with the allocated server.
Networks do not provide allocation of the special computers organizing work of a network. Each user, being connected to a network, allocates in a network any resources (the disc space, printers) and is connected to the resources given in a network by other users.
All users independently decide, what data on the computer to make popular on a network. These networks are rather simple, since each computer is both the client, and a server. There is no necessity for a powerful central server or for other components obligatory for more complex networks.
Networks on the basis of a server became the industrial standard. Networks with the allocated server, despite of complexity of adjustment and relative dearness, allow to carry out the centralized management.
The Internet and Modern Life
Home computers are the latest vogue today. Millions of people around the globe have personal computers nowadays.
In the very beginning, computer systems were only occasionally networked, later they were networked using a number of completely different protocols to connect one system with another. It became the biggest minus for the systems used that time that is why a unified standard was introduced and today we use only standardized protocols. Today the Internet is a common thing. It's on television, in magazines, newspapers, advertisement, our mobile phones, cars, etc. The Internet has already entered in our ordinary life. Everybody knows that the Internet is a global computer network, which embraces hundred of millions of users all over the world and helps us to communicate with each other. Today even using your sell phone you can connect to the Internet and send e - mails, pictures and some music compositions. E - mail is the most widely used Internet application. For some people, it is their most frequent form of communication.
The history of Internet began in the United States in 1969. It was a military experiment, designed to help to survive during a nuclear war, when everything around might be polluted by radiation and it would be dangerous to get out for any living being to get some information to anywhere. Information sent over the Internet takes the shortest and safest path available from one computer to another. Because of this, any two computers on the net will be able to stay in touch with each other as long as there is a single route between them. The technology was called packed switching.
Invention of modems, special devices allowing your computer to send the information through the telephone line, has opened doors to the Internet for millions of people.
Most of the Internet host computers are in the United States of America. It is clear that the accurate number of users can be counted fairly approximately, nobody knows exactly how many people use the Internet today, because there are hundred millions of users, and their number is constantly growing.
Nowadays the most popular Internet service is e - mail. Most of the people use the network only for sending and receiving e - mail messages. They can do it either they are at home or in the internet clubs or at work. Other popular services are available in the Internet too. They are news, available on some dedicated news servers, telnet, game servers, etc.
In many countries, The Internet could provide businessmen with a reliable, alternative to the expensive and unreliable telecommunications systems its own system of communications. Commercial users can communicate cheaply over the Internet with the rest of the world. When they send e - mail messages, they only have to pay for phone calls to their local service providers, not for international calls around the world, when you pay a good deal of money.
But saving money is only the first step and not the last one. There is a commercial use of this network and it is drastically increasing.
However, there are some problems. The most important problem is security. When you send an e - mail, your message can travel through many different networks and computers. The data is constantly being directed towards its destination by special computers called routers. Because of this, it is possible to get into any of the computers along the route, intercept and even change the data being sent over the Internet. But there are many encoding programs available. But, these programs are not perfect and can easily be cracked.
Other very serious problems are spam and viruses. Scientists try to solve this problem but vainly. Their efforts sink in the deep ocean of competition of defensive and offensive technologies.