Many Web browsers let you print documents, save documents to disk, and search for text strings within documents. In addition, many let you view the HTML version of the document and examine the actual HTML code used to create it.

A Web browser receives raw HTML or other data and formats the material or starts another application such as a video player. In most cases you need to configure, or verify the configuration of, Helper applications from within the Web browser itself. Web clients are also responsible for interacting with non-Web servers such as Gopher or FTP directly and they create a virtual HTML document while doing so.

Browsers and Keyword Searches

The Web consists of documents and links. Indexes are special documents which, rather than being read, can be searched. The result of such a search is another virtual document containing links to the documents found. The browser uses the URL you enter and the HTTP protocol to request a keyword search by a remote information server.

The Web contains documents in many formats. HyperText documents (real or virtual) contain links to other documents or to places within documents. All documents, whether real, virtual, or indexes, look similar to the reader and are contained within the same addressing scheme.

A Few Popular Browsers

There are a lot of browsers for the World Wide Web. The most popular browsers include WinTapestry (part of SuperHighway Access), Netscape Navigator, Mosaic, Lynx, Cello, Microsoft Internet Explorer, and Emacs w3 mode.

You should be aware however, that not every Web browser works in the same way. Some browsers support graphics, while others do not. Some have extensive formatting support features while others have just a few. And, some do not support more advanced features such as mailto and forms.

When you create an HTML document, it’s helpful to have several browsers available for testing purposes. This way you can check the appearance of your document on different browsers and make improvements if needed.

Note that most of the browsers listed here are available as shareware or demonstration versions. Once you install your initial browser, you can access others and download the software from various browser vendor web sites.

Terminal-Based Browsers

There are also terminal-based browsers available, such as these:

WWW Line Mode Browser — This program gives Web readership to anyone with a stand-alone terminal. It is a general purpose information retrieval tool. This browser can be used as a test tool for the CERN Library of Common Code.

Lynx — A full screen HyperText browser for character-based display devices such as VT100 terminals and emulators. Lynx uses arrow keys to navigate among embedded links that Lynx displays in reverse video. Lynx also supports forms.

Emacs W3 Mode Browser — This browser runs on systems that support an extensible Emacs. The Emacs w3 mode supports multiple fonts, bold and italic type, and mouse operations. It also has forms support. This browser is compatible with Mosaic so you can use the same hotlist file, history file, and personal annotation directory.

Windows, X Windows, and Macintosh Based Browsers

WinTapestry — SuperHighway Access includes WinTapestry™, a multi-protocol browser integrating WWW, Gopher, CSO, and WAIS and enabling users to access a myriad of Internet resources with the click of a button. In addition, SuperHighway Access gives users the ability to initiate multiple Browser sessions for concurrent information retrieval from the Internet.

Cello — Cello is a windows multipurpose Internet browser that allows access to information resources of the Internet. It supports World Wide Web, Gopher, FTP, CSO/ph/qi, and Usenet News. It supports other protocols such as WAIS, TELNET, and TN3270 through external clients and public gateways. You can use Cello to view hypermedia documents, including inline images, text, and digital sounds and movies.

Mosaic — Mosaic is the best known of the Web browsers and is available on a variety of platforms. It supports inline graphics in GIF or XBM format. Mosaic sends file types that it cannot handle (such as MPEG movies and PostScript documents) to external media players. Mosaic also supports forms.

Netscape Navigator — Netscape Navigator is a full color graphical browser that provides up-to -the-minute browser features for X Windows, Windows, and Macintosh. Netscape includes full forms support, full clickable image support, and an integrated news reader. Netscape also includes non-standard HTML tag extensions to manage screen layout, font size, and image handling.

What is a Web Server?

Technically, a Web server consists of hardware and software. To build your own Web server, you install the software specific to your particular computer or local area network (LAN), and the operating system (or network operating system) you’re running. For example, if you’re running OpenVMS, you need to install and configure Purveyor Encrypt WebServer software for OpenVMS.

Additionally, an Internet connection is required and available via an Internet Service Provider. Once configured, a Web server "serves" documents to browsers over the Internet or over the Intranet via your LAN.

Web Server Tasks

Web servers can perform a number of tasks, such as:

• Logging activities
• Authenticating users
• Recording the Internet address, time, and the request made for each connection
• Protecting certain files from non-authenticated users
• Forwarding requests for data that neither the browser nor the server can access directly to applications called gateways

Web Server Protocol

All Web servers use a language, or protocol, called the HyperText Transfer Protocol to communicate with Web browsers. (This explains the http in a Web URL.)

HTTP is an English-language protocol based on a request/response model. The Web browser makes a request to the server in the form of simple commands, such as GET and PUT. The server responds to the GET command by sending the browser a particular file that’s stored on its hard drive. It’s important to note that HTTP is a stateless protocol; there is no continuous connection between the client system’s browser and the server. If a Web server site is extremely busy, it can sometimes be difficult to establish a connection.

You can exchange all types of data using the HTTP protocol. For example, you can exchange HTML documents, graphics, sound, and video.

Data Types

Data types are identified by the server and preceded by a Multipurpose Internet Mail Extensions (MIME) header.

Web browsers convert open URL commands into HTTP GET requests. So if you type http://smile.mycompany.com/doc.html, the browser:

• Converts this to a GET doc.html command
• Connects to the Web server running on smile.mycompany.com
• Issues the command and waits for a response
  

The response is the requested document or an error message. (If the server is down or the file is no longer available, the Web browser displays an error message indicating that the request can’t be responded to.)

Simulating a Simple Web Browser

You can simulate a simple Web browser by using the TELNET protocol. You use TELNET to connect to a Web server and specify port 80. Include the Web server name and the Internet address. Then type GET, the name of a file that exists on the server, and its path if necessary. After the server returns the document or error, the connection closes.

Servers and Gateways

A gateway is the hardware that handles communications between two different networks. With gateways, the Web can support data types and resources not even conceived of when it was invented. For example, gateways allow Web browsers and servers to function as relational database clients.

The browser gathers data, usually using an HTML form, then sends the data to the server with the name of a gateway program to be run. Then the gateway reformats the data and sends it to an information server. The gateway receives a response, reformats that response as an HTML document, and delivers the response to the Web browser.