http://www.domain.com or http://domain.com ?

[dr_smith]

This is one of those things that I really should know but I don't.

http://www.domain.com
http://domain.com

Can anyone tell me the difference between these 2 forms of URL? What is the function of the www? Some sites require the www, others don't.

Many thanks.

[Rincewind]

These days the only difference is that one has www and the other does not.

There are many uses for domain names. They are not always used for web traffic. For example, you'll commonly see ftp.example.com, mail.example.com or ns1.example.com. The www bit was used to point the dns system to the web server of that domain.

It is common nowa days to point dns for example.com to the webserver. Indeed it's common for all the servers (ftp, ssh, mail, and web) to all be on the same IP so the extentions are irrelevant. (the system picks up the port and the http:// or fttp:// bit to know which server you want.) But lets imagine you were a amazon sized company. You would have many servers for 1 site. So different sub domains would point the dns to those different machines. In which case, www.example.com would be a different place form ftp.example.com. Only convention says that example.com should point to a web server. It could point to any server you wanted.