Computers on the Internet

In the IBM PC world commands like copy are not case sensitive. This means that you can type the command using any combination of upper and lower case letters. The UNIX world is different -- often it is case sensitive, requiring specific case when referencing its resources. Many of the computers used on the Internet are UNIX based systems. This premise is important to remember while reading the remainder of this paper.

When working on the Internet, you need a way to access a document that is sitting on some computer in some directory. This document can be on a Mainframe, Mini or PC computer. It can be found on a computer that has an operating system different than yours -- UNIX, Windows NT, Mac OS, or one of many other operating systems. Each system stores and names files differently. To overcome this problem, the URL concept was instituted. Every document, query, graphic, FTP file, Gopher site, etc. are assigned a unique Uniform Resource Locator or address.

A URL can point to a file in a directory and that file and directory can exist on any machine on the Internet and this file can be served via any of several different methods. As pointed out, it can be more than a file, it can be query, a gopher server contents, and on and on.

The servers of the Internet

There are several types of computers on the Internet, they are joined together as one single network. Each computer that exchanges or transfers information on the Internet is known as a server. In fact, the Internet is the largest Client/Server database in the World. There are thousands of servers available on the Internet.

There are several different types of servers on the Internet, each running their own server software. The four basic types of servers are:

HTTP, or HyperText Transport Protocol, server

Used to store and send standard World Wide Web hypertext documents. HTTP is a simple protocol which is the basis of the Web.
FTP, or File Transfer Protocol, server

Used to store and transfer files across the Internet. These servers are the file libraries or archives, which can be used by the public. These can be program files or documents.
Gopher server

Used to accept requests for information and then scan the Net for it. A Gopher server lets the user work through menus, instead of typing in long sequences of characters. It works in conjunction with FTP sites letting a user select a file from a menu. It is normally based on a single database.
WAIS, or Wide Area Information, database server

WAIS is similar to a Gopher server; however, it lets users access and find files using a single interface. The WAIS server program worries about how to access information on hundreds of different databases.

Each of these servers can store different types of documents and files. Once a server is on the Internet, it can be accessed by the millions of users of the Internet.

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