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Internet
There are three information revolution in the history of mankind: the first was caused by the invention of writing, the second - the printing press. We are now at the beginning of the third information revolution, which in the future should be a qualitative change in the conditions of human life. It is connected with the emergence of a global information network Internet, is considered one of the most impressive creations of modern engineering. This network was formed before our eyes in the last two decades of the XX century by combining a plurality of local and regional computer networks.

The earliest local area networks emerged in the 60s. Each of them is a system of computers of any organization or company, located in one or several nearby buildings and connected by special cables, allowing them to exchange information. Local area networks have become the further development of local networks. It was a collection of several LANs, connected with each other. Using these, it was possible to receive and send information beyond its system. The Internet is a logical conclusion of this process. It is linked in a single system, tens of thousands of private, commercial, academic, government, and other information networks around the world, that is, in the full sense of the word has become a network of computer networks.

Start of the Internet, put in January 1969 the US government. This year, a group of scientists (their work was funded by the Office of Advanced Studies (ARPA), which is a division of US Department of Defense) brought together into a single system multiple computers - keepers strategic information. For the US government, this system was convenient because it ensured the smooth operation of computers even in the event of nuclear war. ARPANET system initially only linked scientists with remote computer centers. But it soon became clear that it could serve as a very convenient way to send e-mail and exchange information. By 1980, for example, ARPANET was created by several other national computer networks that connect different communities, groups and organizations (eg, CSNET brings together researchers in computer science and programming). In 1983, the ARPANET was split into two networks - ARPANET and MULNET.

MULNET system was reserved for military use, while the ARPANET was used for peaceful and scientific purposes. system of information exchange between them was provided. This association was called the Internet. Initially, all the national computer network in the United States there were separate from each other, but gradually one after the other connected to the Internet. Finally in 1986 the US National Science Foundation has linked scientists across the country with five supercomputers located at various scientific centers. High-speed computer networks linking these supercomputers, formed the core network under the name NSFNet. She became like a backbone, the foundation and the main part of the global computer network, which is now known as the Internet. In the next decade, as the connection to the network a variety of other regional and national computer networks, the Internet has evolved into a huge system that covers the entire globe.

First we used the Internet only to specialists, but gradually the number of users Network has expanded, and now at his disposal treated people of different professions. It housewives, lawyers, writers, athletes, police, gardeners, cooks, businessmen, students, etc. Their interest in the Internet due to the fact that it can really provide the information necessary and interesting to everyone. The Internet provides many different services such as the ability to access different databases, search the library of information, use e-mail, etc. Once connected to the Internet, each user gets quick access to vast information resources accumulated by mankind. It can browse the catalogs of the largest libraries in the world, learn the latest news, receive copies of various documents, to discuss his concerns, to establish contacts with colleagues from science and business. It can receive and send messages from anywhere in the world, to read news and posts dedicated to the thousands of different topics, to find any documents, books, photographs, sound recordings and films, meet new people, get to know the prices for products of interest to him and much more. For example, it requires some kind of software for your computer - can be contacted with any university and copy the program to their computer. You can contact any museum, to get information about some exhibits. You can connect to the remote library. You can get the official reports, newsletters, communiqu├ęs and reviews of various community and government organizations. You can subscribe to one of the many news programs and receive the latest posts - even before they get on TV or in the newspaper. However, the most popular application of the Internet now is e-mail, because now it is the fast, economical and easy way of transferring information between people - at a price below a postage stamp. What is entered in the data bank in one part of the world, the other in a few seconds can be read and put into print. Moreover, messages can contain not only text, but also drawings, photographs, audio - and video recordings, documents and programs.

In order to connect to the Internet, you need three things: a computer, a telephone and a modem. Modem - a "carrier" of information between the computer and the telephone exchange. It is needed because the phone and computer transfer data two incompatible ways. The computer "talking" figures, ie, stores and manipulates the information provided in the form of numbers. The telephone network operates on analogue signals which are represented on the oscilloscope screen in the form of waves. When one computer sends data to another computer via a telephone network, computer modem converts the number into an electrical signal. Conversely, when the information reaches the telephone modem, it converts it into a digital form that is understandable to the computer. Just like the computer to which it is connected, the modem is useless without programs that control its operation.

Physically, the core network is a huge number of computers connected by a cable and can communicate. information transmission lines can be very different this fiber optic and telephone cables, microwave and satellite communication systems. As a rule, personal computers of individual users do not go directly to the core network and are connected to a special host computer, which belongs to an organization or a private company and is called a file server. It performs three functions: 1) it stores frequently used programs and other interesting information that can be obtained; 2) he plays the role of controller - receives information that some users wish to transfer to the recipient, and sends it to him; 3) it serves as a gateway to other computer networks. Thus the host computer may be, for example, college computer, connect to the Internet computers faculties, teachers or students. (In 1994, on the Internet, there were already 5 million computer nodes, and in the US alone, there were more than 2 million, by which time the global network brings together about 55 million users worldwide.) Each host computer and a personal computer user get online your address. Address includes at least two parts: the user's own address and the host computer (the latter has a complex structure and includes, for example, country name, name of the branch network in that country's own address and the host computer). In essence, connect directly to the Internet and can be a simple user - it is enough to have a high-speed modem, but the connection is expensive (several thousand dollars), and the monthly fee is also very high (about a thousand dollars). Therefore, usually it is not practiced to the same clock speed Internet access, as a rule, the average user is not necessary.

Data transferred over the Internet as follows: from the personal computer individual user, they fall into a local or wide area network from it - in the basic Internet and it is transferred anywhere, then transmitted to the local territorial network and finally back to the computer specific user. As highway and in the lines used to transmit digital data from one computer to another, there are speed limits. This transmission rate information is called bandwidth. Lines with high bandwidth to transmit more information per unit time than the lines with a narrow bandwidth. In general, computer lines transmit information at a rate of hundreds of thousands or millions of bits per second, while the most advanced close to the speed of one billion bits per second.

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