404 error code and what it means

We've all received an error like the one shown below:

File not found - requested URL not found on this server

It's annoying, especially when you've searched for something and found what looks like the perfect site. At least the description exactly matches your needs. You click and boom, a 404 error appears.  Whoops. What happened to that perfect site?

There are several reasons why this error occurs. I guess the thing that you need to remember is the internet is very fluid. In fact, it changes constantly. Sometimes a site is changing while you are looking at it. I can remember several times I was examining a site and returned to a page that I had seen only moments before and found it to be different! That can be very unnerving, to say the least.

So what sometimes happens is a webmaster changes his site around and obsoletes links. If he's a rank amateur, he'll break links within his own site.  This does happen sometimes, but any webmaster worth his salt is constantly checking and rechecking his site to be sure it works and works well. After all, the only way to test something is to use it. And the only way to see if a site really works is to surf it.

More often, someone has linked to a site and that site changes. Since it can be difficult if not impossible to determine who has linked to a site, links break. 

Now, really good webmasters never ever delete a page on their site. What they do is create redirect pages. Thus, if I have a page called "barbi.htm" and I want to delete it, I will modify the page to tell the visitor it no longer exists and redirect him to another page in my site. This way I will not lose traffic simply because I've deleted or renamed a page.

This constant checking of one's own web site will also catch another common error: misspelling a hyperlink. When I create a hyperlink, I either browse to the target using my web editor, or I cut and paste the link directly out of Internet Explorer. I never type the hyperlink in myself, which reduces the possibility of error greatly!

Also common is the webmaster who does not understand that many servers are case sensitive. This means that "Richard" is not the same as "richard". You will see this sometimes if a webmaster moves a site from a server which is not case sensitive (VAX/OpenVMS) to one that is (Unix).

Sometimes a site simply moves to another host. This frequently happens when a site outgrows it's host. I know of one site that had to move several times because it's bandwidth demands became huge! According to the webmaster this site was getting tens of thousands of visitors every day, and all of them were downloading tremendous amounts of pictures. He was booted off one server with no notice and no backup and had to rebuild his site from scratch! This kind of event will certainly cause 404 errors!

More rarely, a webmaster has been in the process of uploading his site when his upload software crashed. This may leave broken links for a short time until the problem is fixed.

Generally an ISP will provide, at least for a short time, a redirect page to a new site. You will see this as a "My site has moved. If you are not transported in 10 seconds click here" message.

And of course some sites simply shut down. This is actually getting more rare as it's often more expensive for an ISP to delete old data than it is simply to prevent updates.

Search engines are notorious for their broken links. You have to remember that most search engines only examine web sites every month or so (sometimes the delay is as long as six months). Because of this, all of the above problems can occur, leaving broken links.