Why do some website addresses have “www”, and some don’t? And why do some work with or without the “www”?
Most of the time, it’s an oversight. Occasionally, it’s on purpose, but to be honest, I haven’t run across an “on purpose” in years.
It’s common practice now that “www” is optional; mostly because it’s redundant and URLs are long enough without adding redundant information.
But once upon a time, there was a reason.
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The original intent was that the “www” specified what you were trying to do, so you could be sent to the right computer to do that. Servers that were available for “World Wide Web” access used a “www” prefix. Servers that were available for “File Transfer Protocol” access used a “ftp” prefix. Even on the same base domain, www.example.com and ftp.example.com might well be completely different machines. The prefix was both a mnemonic device to help us remember what we’re doing as well as a way to route us to the right server.
The question, of course, is what to do when no prefix is specified. The way internet names work, www.askleo.com and askleo.com are technically two different names and two different sites. As the owner of the base domain name askleo.com, I needed to take a couple of extra steps to make them both behave the same way when you visit either with your browser.
Over time, the web and all those “www” servers became the predominant traffic on the internet, so more and more sites began to respond to references both with and without the “www.” As I said, it’s become common practice, almost a pseudo-standard.
But unfortunately, “common practice” doesn’t imply 100%.