Why do some Web sites include www in the URL while others don't?

A "normal" Web site has a URL that looks like this: https://www.howstuffworks.com. You may have noticed that on many sites, the "www" part is not required. You can just as easily use https://howstuffworks.com to get to HowStuffWorks. There are other sites that have extra layers of naming, such as http://www.delphion.com and http://journal.iftech.com, that seem to use a different word besides "www" to reference different Web sites. Another common thing you see is a name like ftp.microsoft.com, used either with the FTP command or as a URL (ftp://ftp.microsoft.com) in a browser.

If you have read the article How Web Servers Work, then you know about name servers and IP addresses. A name server translates a name to an IP address. When you type a URL like https://www.howstuffworks.com into your browser, the browser contacts its default name server and asks, "Have you ever heard of www.howstuffworks.com?" If this is the first time the name server has heard of www.howstuffworks.com, it finds the .com name server and asks if it knows of the name server handling howstuffworks.com. If so, your name server connects to the name server for howstuffworks.com and asks it about www.howstuffworks.com. If the HowStuffWorks name server has a listing for the www prefix, it returns the IP address for "www.howstuffworks.com" and your browser connects to that IP address.

The network administrator for the domain "howstuffworks.com" is in charge of mapping the names in the howstuffworks.com domain to specific machines and their IP addresses. In many large companies, there will be different machines (with different IP addresses) handling WWW, FTP, Telnet and other traffic. On smaller sites, the same machine can handle everything.

The network administrator makes a list of names and IP addresses, like this:

The­ administrator can put anything in that list, because the name servers don't care. The administrator could put in scooby.howstuffworks.com, scooby.doo.howstuffworks.com and scooby.dooby.doo.howstuffworks.com, and when someone types in those names the name server will return the IP addresses associated with them.

In the case of Web sites that happen to work without the "www" prefix, it simply means that the administrator has decided that if there is no prefix, the IP address returned should be the IP address for the Web server.

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