第25课听力
UNIT 25 Internet The Internet is a giant network of computers located all over the world that communicate with each other. The Internet is an international collection of computer networks that all understand a standard system of addresses and commands, connected together through backbone systems. It was started in 1969, when the U.S. Department of Defence established a nationwide network to connect a handful of universities and contractors. The original idea was to increase computing capacity that could be shared by users in many locations and to find out what it would take for computer networks to survive a nuclear war or other disaster by providing multiple paths between users. People on the ARPNET (as this nationwide network was originally called) quickly discovered that they could exchange messages and conduct electronic "conferences" with distant colleagues for purposes that had nothing to do with the military industrial complex. If somebody else had something interesting stored on their computer, it was a simple matter to obtain a copy (assuming the owner did not protect it). Over the years, additional networks joined which added access to more and more computers. Today thousands of networks and millions of computers are connected to the Internet. It is growing so quickly that nobody can say exactly how many users "On the Net". The Internet is the largest repository of information which can provide very very large network resources. The network resources can be divided into network facilities resources and network information resources. The network facilities resources provide us with the ability of remote computation and communication. The network information resources provides us with all kinds of information services, such as science, education, business, history, law, art and entertainment,etc. The goal of your use of the Internet is exchanging messages or obtaining information. What you need to know is that you can exchange message with other computers on the Internet and use your computer as a remote terminal on distant computers. But the internal details of the link are less important, as long as it works. If you connect computers together on a network, each computer must have a unique address, which could be either a word or a number. For example, the address of Sam's computer could be Sam, or a number.The Internet is a huge interconnected system, but it uses just a handful of method to move data around. Until the recent explosion of public interest in the Internet, the vast majority of the computers on the Net use the Unix operating system. As a result, the standard Unix commands for certain Internet services have entered the online community's languages as both nouns and verbs to describe the services themselves. Some of the services that the Internet can provide are: Mail, Remote Use of Another Computer (Telnet), File Transfer, News, and Live Conversation. The most commonly used network service is electronic mail (Email), or simply as mail. Mail permits network users to send textual messages to each other. Computers and networks handle delivering the mail, so that communicating mail users do not have to handle details of delivery, and do not have to be present at the same time or place. The simplest way to access a file on another host is to copy it across the network to your local host. FTP(File Transfer Protocol) can do this.Presently, a user with an account on any Internet machine can establish a live connection to any other machine on the Net from the terminal in his own office or laboratory. It is only necessary to use the Unix command that sets up a remote terminal connection (Telnet), followed by the address of the distant machine. Before you can use the Internet, you must choose a way to move data between the Internet and your PC. This link may be a highspeed data communication circuit, a local area network (LAN), a telephone line or a radio channel. Most likely, you will use a Modem attached to your telephone line to talk to the Internet. Naturally, the quality of your Internet connection and service, like many other things in life, is dictated by the amount of money that you are willing to spend. Although all these services can well satisfy the needs of the users for information exchange, a definite requirement is needed for the users. Not only should the users know where the resources locate, but also he should know some operating commands concerned to ease the searching burden of the users, recently some convenient searching tools appear, such as Gopher, World Wide Web (WWW) and Netscape. WWW is a networked hypertext protocol and user interface. It provides access to multiple services and documents like Gopher does but is more ambitious in its method. A jump to other Internet service can be triggered by a mouse click on a "hotlinked" word, image, or icon on the web page. As more and more systems join the Internet, and as more and more forms of information can be converted to digital form, the amount of stuff available to Internet users continues to grow. At some points very soon after the nationwide (and later worldwide) Internet started to grow, people began to treat the Net as a community, with its own tradition and customs. For example, somebody would ask a question in a conference, and a complete stranger would send back an answer: after the same question were repeated several time by people who hadn't seen the original answers, somebody else gathered list of "frequently asked questions FIQ" and placed it where newcomers could find it. So we can say that the Internet is your PC's window to the rest of the world. |
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