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Electronic mail, of course, is a rather unglamorous function of the Internet. Most of the hoopla surrounding the Internet concerns Web pages, accessed via Web browsers. To understand these terms, a little background is in order.
By the end of the 1980s, most of the infrastructure that was to become the Internet was already in place—primarily, the nationwide linkage of computers that could almost instantaneously access other computers on the network. Before that, things like mail and newsgroups were passed along from computer to computer (mostly overnight, when phone rates were lower). When the Internet finally took shape, it became possible to access any other internetworked computer directly.
Armed with these capabilities, CERN researchers, lead by Tim Berners-Lee (now head of the WWW Consortium at MIT), developed an information-exchange structure called the World Wide Web, which would take advantage of these instantaneous links. A computer on the Internet has a distinct address, and a piece of software (called a Web browser) would use that address for instant connectivity. Pages on that internetworked machine are formatted in the HyperText Markup Language, or HTML (itself a subset of the complex Standard Generalized Markup Language, or SGML). This formatting would specify things like headlines, body text, and hypertext links to other Web resources.
It’s up to the local Web browser to actually render this Web page on the local computer. For example, the Web browser will contain a tag for a headline; the Web browser uses a local font to create this headline. The same goes for body copy and hypertext links.
Popular Web Browsers
Mosaic from NCSA was the first popular Web browser, and for many users it still epitomizes the power of the Internet. Of late, however, Netscape Navigator has garnered a lot of attention as being the cutting-edge Web browser.
We’re not going to play favorites here; you need to go out and grab whichever Web browser you want. We’ll use Netscape Navigator in our examples, but there’s nothing that wouldn’t apply equally to NCSA Mosaic. In fact, there’s a whole list of freeware Web browsers that have been compiled for use under Linux; you can grab them via FTP (which we’ll describe later in this chapter); we’ve included the noncommercial ones on the second CD-ROM. They include:
By and large, the World Wide Web is a graphical beast; most of these Web browsers (the big exception is Lynx) run under the X Window System.
Page Limits
At its core, the World Wide Web is actually an ingeniously simple thing. A Web browser, such as Mosaic or Netscape, sends a request over the network to a Web server; the request can be in one of five formats (as listed in Table 9.2 later in this chapter). The server then honors the request by sending a text file formatted in the HyperText Markup Language (HTML), which inserts tags in the text. The text file is then rendered by the local Web browser, which matches the tags to resources on the local machine—for example, a tag for TITLE would be rendered in a font and point size set up through the Web browser.
| Format | Represents |
|---|---|
| file://ftp.microsoft.com | File at an ftp site |
| ftp://wuarchive.wustl.edu/mirrors | FTP site |
| http://info.cern.ch:80/default.html | WWW site |
| news:alt.hypertext | Usenet newsgroup |
| telnet://dra.com | Telnet connection to Internet-connected server |
The HTML language also allows graphics and hypertext links to be embedded in the document. Most graphics files are in the GIF and XBM file formats. The hyperlinks are noted with their own tags and are usually set in a different color within the rendered document. For example, under a heading titled Other Resources, there may be a line colored blue that says Sun Microsystems Home Page. To the Web browser, however, there’s an embedded Web address (in this case, www.sun.com). Double-clicking on Sun Microsystems Home Page initiates a request to the Web server www.sun.com. You don’t need to know the www.sun.com address; you only need to know how to use a mouse.
You can start Netscape with the following command in an xterm window:
gilbert:/$ netscape &
When Netscape launches, it connects directly to a Netscape Communications home page (home.netscape.com). (By the way, this is a good way to test if Netscape is configured properly; if you or your system administrator has misinstalled Netscape, it will report that a connection to home.netscape.com has failed.)
Chances are pretty good that you won’t want to spend much time wandering around the Netscape Home Page. The beauty of the World Wide Web is that it allows you to jump from Web site to Web site, either those linked to your current page or a page totally unrelated.
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