1. Unit Four Internet 1.Passage One. A Short Introduction

2. Training target: In this part ， our target is to train your reading comprehension. We have made the flexible sentences strong black and marked the subject ， predicate and object of them. Try to grasp the main idea of these sentences.

3. Text. Internet is a giant global and open computer network ， which is a collection of interconnected networks. It is also a way to realize world-wide information exchanging and resource sharing between international computers.

4. The original Internet was ARPANET （ Advanced Research Projects Agency Network ）， which was established by U.S. Department of Defense in1969.The ARPANET was used to share data between some separated military institutes and universities in region. By 1972 the network had expanded to incorporate 40 nodes. ARPANET soon became a forum for the exchange of information and ideas among scientists and academics ， and within a few years the number of computers connected to the network increased to more than100.

5. By the mid-1970s ， many U.S. government agency networks had been linked by ARPANET and ， because the networks were of a disparate nature ， a common network protocol called TCP/IP （ Transmission Control Protocol. Internet Protocol ） was developed and became the standard for internetworking military computers. So U.S. Department of Defense Advanced Research Program Management Bureau ① asked all hosts connected with ARPANET to adapt TCP.IP to be their protocol in1983. In1985 ，

6. the U.S.NSF ① established a specially used net which connected six super computing centers—NSFNET. This is the basic of Internet. With the network developing in all society ， a lot of institutes and universities established their LANs ， and connected them to NSFNET. In1989 ， the ARPANET had been dismissed and the NSFNET had been opened to the public and became the most important backbone of Internet.

7. When the U.S. developing their national net ， the other countries were developing too. At the end of1980s ， interlinkage of different countries’ computer net appears. After that there were countries joining in every year and getting to form the present Internet. The word “Internet” became the common term for referring to the worldwide network of military ， research and academic computers. Now ， there are86countries directly connected with Internet and150countries can access it by E-mail. It is growing so quickly that nobody can say exactly how many users are “On the Net”.

8. First ， let us see how to access the Internet. Access to the Internet falls into two broad categories: dedicated access and dial-up access. With dedicated access ， a computer is directly connected to the Internet via a router ， or the computer is part of a network linked to the Internet. With dial-up access ， a computer is connected to the Internet with a telephone line using a modem.

9. Internet makes all kinds of physical net connection to be a whole one. All computers that adapt TCP/IP protocol can communicate with any computer of Internet and can be looked as a part of Internet. Host is the computer that directly connects with Internet. All the hosts are in equal class in Internet ， no matter they belong to LAN ， MAN or WAN. They are all in equal class in communicating data and sharing resources.

10.  The End