Why does one use "www.foo.com" as a server name? Why not just "foo.com"?
It is a convention. I suggested it early on, in this guide, and I am of two minds about it now. An alias was a better alternative to "pegasus.foo.com" which typically resulted when someone who happened to have a machine called pegasus started to run a web server for foo company. (The www prefix on a computer name also allows one to guess that it was a web server. This allowed early estimates of the numbers of servers, for example.) In those days I suggested an alias www.foo.com for the HTTP server in line with existing Internet practice of ftp.foo.com for the FTP server and mail.foo.com for the smtp server, and so on. These aliases could, even if originally on the same machine, be moved to point to machines of appropriate size as necessary.
You don't have this flexibility of configuration is you point everyone at "foo.com" itself for all services. Typically early webmasters could not have comandeered the "foo.com" address itself.
Nowadays, however, the web server may be far and away the biggest service foo company has, and it might make sense to give it pride of place. Remember you can only do this with one service. You could use http://foo.com/ which is after all easier to type, even though people expect to have to type the "www".
Whatever you do, it is important not to do both. If you do both, you will halve the effectiveness of caching of your pages, as caches won't realise that the page under www.foo.com and under foo.com is the same. What we currently (1999) do in the W3C site it to redirect any traffic to w3.org to www.w3.org. So if you miss out the "www." by accident or for speed, them you end up at the canonical www.w3.org address. I would recommend doing a forward one way or the other whichever you chose as your web site's cannonical definitive address.
This page was originally an answer to a question from David Maggiano <firstname.lastname@example.org>. Thanks, David.©1992-95 Tim BL