Archie， developed by graduate students at McGill University in Montreal， is a system for locating files in FTP （File Transfer Protocol） sites. FTP sites are computers that store thousands of files. Archie （the name comes from the Archie Comic book series） are servers programs running on a main or host computer that gather and index files from FTP sites. Generally you can use Telnet or electronic mail to access an Archie server. If you know what you are searching for， you can ask an Archie to locate a list of files along with the names of the FTP sites at which the files are stored. Once you find a file you are interested in， you generally need to use FTP software to download the rite from the host computer to your computer. You can also use FTP to upload files from your computer to another computer on the Internet. Archie is designed for people who know exactly what they are looking for， but need help to track it down.
3. The World Wide Web
The World Wide Web （WWW） is an information retrieval system that uses the concept of hypertext. Instead of browsing through menus， WWW displays text with specially marked words or phrases that are actually kinds to the topic being discussed. In this way， you can trace a chain of information through a series of files located in computers around the world.
4. The Internet
Electronic mail， electronic conferencing and compute-based collaborative work are the forerunners of what some people are calling electronic communities， which would link groups of scientists， researchers， business people， and students with information and access to colleagues around the world.
The foundation for electronic communities is already in place. The Internet is a high speed world wide network linking over two million computers with somewhere between 15 and 20 million individual users in 137 countries. It is， in fact， a network of more than 1 000 computer networks loosely connected in the United States via the National Science Foundation Network （NSFNET）， the Internet’s high-speed （45 million bits per second） backbone.
There are many ways to connect to the Internet. As previously mentioned， the simplest connection is via a terminal emulation program such as Telnet and a modem. You can also access the Internet through commercial services such as Computer Serve or MCI Mail， which provide an Internet gateway， but this connection is sometimes limited to sending and receiving electronic mail messages. Businesses and large organizations often use commercial access to provide such as Delphi， Netcom Online communications Services， and UUNET Canada to provide their Internet connection. If you work for an organization that subscribes to a commercial access provider， you probably already have access to the Internet. Many colleges and universities are linked to the Internet and students are often given tree Internet accounts that enable them to collaborate with students and professors around their university and around the world. At the expensive end of the spectrum is a direct connection， typically involving a very high-speed modem or direct line with which you dial in， connect， and become a part of the Internet.
Your type of connection depends on such factors as the type of network you use， your relationship to an institution that is already connected to the Internet， and the amount of money you want to spend.
Once you’ve made the Internet connection， you can send electronic mail to any of millions of other computer users all around the world. You can participate in collaborative newsgroups through UseNet， a protocol that determines how groups of messages can be stored and distributed among computers. Newsgroups are organized into a hierarchy consisting of major topics and subtopics and feature a diverse variety of subjects ranging from electrical engineering to Shakespeare to television soap operas to AIDS. You can “surf” the net， which refers to looking for new information and resource with no particular goal in mind. Finally， you can access thousands of databases available over the Internet.
What kinds of applications are available on the Internet？ In addition to electronic mail， which has already been discussed many other applications have evolved in response to the explosive growth of the Internet. These applications facilitate access to networked electronic information sources and are designed to help you navigate through the wealth of information available on the Internet.
5. Protocols
For two devices to communicate， they must “speak the same language”. What is communicated and how and when it is communicated must conform to some mutually agreed-upon conventions. A protocol is a formal set of rules for specifying the format and relationship when exchanging data among communicating devices.
Because communication between dissimilar devices is extremely complex， it is desirable to standardize protocols so that any device can use them. Two systems， no matter how different， can communicate if they use standard protocols. Also， a set of protocols instead of a single protocol is usually needed. There protocols are arranged in a hierarchy of layers. The top layers provide service in support of the applications;the bottom layers are connected with transmitting information between communicating devices. For example， TCP/IP （Transmission Control Protocol and Internet Protocol） are two of the most important protocol layers used to create， address， send and reassemble packets of information among computers on the Internet Network.
By treating each layer independently， it becomes possible to change a protocol at one layer without affecting the other layers. For example， as higher-speed communication technology emerges， only the lower-level protocols need to change. The application can continue to function without having to know the details of the physical communication channel.
【Vocabulary】
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