Web Ch2- Introduction to WWW, Con't...

1.6 Web Servers

The World Wide Web is built upon a protocol called Hypertext Transport Protocol (HTTP). HTTP is designed to a small, fast protocol that is well suited for distributed multimedia information systems and hypertext jumps between sites.

The web consists of pages of information on hosts running web-server software. The host is often referred to as the "web server," which is technically inaccurate. The web server is actually software and not the computer itself. There are version of web server software that can run on almost all computers. There is nothing intrinsically special about a computer that hosts a web server, and there are no rules dictating what hardware is appropriate for running a web server.

The original World Wide Wed development was all performed under different flavors of UNIX. The majority of web servers still run on UNIX boxes, but this is changing. there are now web server versions for almost every major operating system. Web servers hosted on high performance operating systems, like Windows NT, are becoming more and more popular. This is because UNIX is still more expensive to run than Windows NT and is also more difficult to use for the average user. Window NT has proven itself to be an efficient, reliable, and cost-effective platform for hosting web servers. As a result, NT's slice in the web server operating system pie is growing.

Connections to web servers are made on an "as needed" basis. If you request a web page from a web server, an IP connection is made over the Internet between your host and the host running the web server. The request web page is sent over that connection and, as soon as the page is received, the connection is broken. If the received page contained references to additional information to be downloaded, each would be retrieved using a new connection. A web page with five pictures in it, therefore, takes at least six requests, or hits, to retrieve it all.

Web servers are often not the only IP-based applications running on a single host. In fact, aside from performance issues, there is no reason why a single host cannot run multiple services. For example, a web server, FTP server, DNS server, and a SMTP POP3 mail server can run at the same time. To ensure that each server application only responds to requests and communications from appropriate clients, each server is assigned a port address. If IP addresses are like street addresses, ports can be thought of as apartment or suite numbers.

Most servers use a standard set of port mappings, and some of the more common ports are listed in the table bellow. Most Web servers use port 80, but you can change that. If desired, web servers can be installed on nonstandard ports to hide web servers. You can also host multiple web servers on a single computer by mapping each one to a different port. Remember that if you do use a nonstandard port mapping, users will need to know the new port number to be able to connect to your server.