DK Science: Internet
The Internet is a computer network covering the whole world. We can use it to search through three billion pages of the WORLD WIDE WEB, or to keep in touch with people by EMAIL. Unlike other networks, the Internet is not under anyone?s control. It is held together by a set of standards, or rules, that set out how computers connected to it should exchange information.
Table7.HISTORY OF THE INTERNET
|1963||Arpanet created to link US research computers|
|1970||Packet switching first used|
|1978||TCP/IP protocols established for communication and data exchange|
|1983||TCP/IP made compulsory, effectively creating the Internet|
|1990||World Wide Web protocol created|
Data is sent across the Internet as small packets. Each packet travels by the best route available, avoiding busy or broken links. Computers linked to the Internet handle data using agreed protocols (procedures). The most important are TCP (transfer control protocol) and IP (Internet protocol).
People on the move or without their own computer can connect to the Internet at an Internet caf. They pay a small fee to use one of the caf?s machines. Public wireless points make it even easier to get connected. A wireless-enabled computer can access the Internet through a radio link in the caf or another public place. You can also connect to the Internet through a mobile phone.
Your computer does not connect directly to the Internet. Usually, it connects through telephone wires to an Internet service provider (ISP). Your computer is linked with one of theirs, which has a unique address on the network. Anything you want to see goes to this address first, then to your computer.
Email (short for electronic mail) is an electronic postal service. It was invented in 1971, and works on any computer network but is now mostly used on the Internet. A message starts from and ends up at a mail client ? the program used to write and read emails on a computer. In between, it is handled by one or more mail transfer agents. These are computers that pass the email on until it gets to the electronic mailbox specified by its email address. An email is not private because it may pass through many computers before it arrives, giving other people a chance to read it.
The World Wide Web is a collection of billions of files held in a huge number of computers, all linked to the Internet. The files may contain words, pictures, sounds, or almost anything else. They are linked to each other by hypertext ? a way of making a word or picture in one file call up another file anywhere in the world.
Websites such as this are written in a computer language called hypertext mark-up language (HTML). A computer program called a web browser translates HTML into a neat layout of text and pictures on your screen. To see a web page, you type its address into the address box. If you need to find pages about a particular subject, you can use a search engine. Search engines keep a constantly updated index of every word in billions of documents. They produce a list of pages that might be suitable, and you click on any pages you want to see.
A web address or URL (short for uniform resource locator) tells the browser where to find a file and how to treat it. A slash (/) marks the start of the file?s name. The ?http? says the information is to be handled as hypertext.
The World Wide Web owes its existence to British scientist Tim Berners-Lee. He worked at a research lab called CERN in Switzerland. Frustrated by the difficulty of working with information scattered all over the Internet, he developed hypertext software to link it up. The result was the World Wide Web, which came into public use in 1991. Marc Andreessen created the first easy-to-use web browser in 1993.