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404 Error

Simon Pitt | About | Wednesday 1st April 2009

Whoops. Something has gone wrong, and you've ended up here. Like many websites, Image Dissectors has some links that take you to pages that don't exist. This is a problem with hyperlinks in general, since they are one way links. If a page name is changed, you're left with dead links. And consequently, you end up on 404 error pages like this.

It's normal practice on 404 Error pages to give a link to a sitemap, so the lost visitor can try to find what they're looking for. Image Dissectors doesn't have a sitemap though. Except for this piece of unreadable XML junk or this bland text document, which are for search engines rather than humans. In most cases the reason people end up on 404 error pages is because the content has been removed, or someone has messed up a URI. So, if you know what you're looking for, your best bet is to search the site for it. Your other option is to browse all the articles. That's as close as you're going to get to a readable sitemap on this site.

The 404 error is just one of many responses you can get. 403, for example, means that the server can be accessed, the page is there, but it's too cool for you to look at. 404 means that the server is running fine, but a page with the address you specified doesn't exist. The standard response code is 200, meaning everything is a-okay.

There's quite a nice little story that "404" refers to the room on the fourth floor of CERN where the world wide web databases were originally held. Unfortunately, like all nice little stories, this is complete balls. The CERN room numbers don't even work like that. The initial number refers to the building number not the floor. In fact, building 4 doesn't even have a room 04. Inexplicably, the numbers start at 10. This results in the wonderful irony that if you go to CERN looking for room 404, you won't be able to find it.

It has been suggested that this was an elaborate joke played by TimBL on the whole Internet, since he knew there was no room 404 at Cern. If this is the case, it means Tim foresaw all the problems inherent in links, and was bothered enough to structure his http status codes accordingly to play a very oblique little joke, but wasn't bothered enough to change the implementation so this problem wouldn't occur. So you can believe that myth if you're stupid.

The truth is, HTTP codes were finalised by the good old W3C (World Wide Web Consortium) in 1992, led by father of the Internet Tim Berners-Lee. The code format was, in fact, copied from FTP status codes. However, all of the meanings of the codes were changed except two: 100 (continue) and 200 (okay). Indeed, there was no 404 code in FTP specifications.

Now, let's have a look at what 404 actually means. The initial 4 indicates the nature of the error. A 2 indicates success, a 5 indicates a server-side error and a 4 indicates a client-side error. That is, your computer, at your end, caused the mistake. The 0 represents a syntax error. That is, the address you've typed (or clicked on) won't work for some reason. The final number explains the reason. In this case a 4 means that the server can't find the page. 403, for example, means it's your fault, you've entered an address with syntax that isn't acceptable, and the reason it's unacceptable is because the page is restricted.

Technically, 404 pages are often used incorrectly. A page that has been permanently moved should result in a 410 error. However, 410 errors are so uncommon on the Internet you might as well not even believe in them.

404 errors are one of the few (if only) http header responses to come through to common parlance. Apparently, "404" is 'often' used in conversation to mean vacant or empty (although, I have to admit, I've hung around with some very geeky people, and even they have never said that). It is also increasingly common for websites to produce humorous 404 pages that reflect the style or attitude of the site.

Status Codes:

I was talking to someone the other day, who asked why there was only a 404 error, why wasn't there a 403 or a 405, or a 304. Obviously he thought this was a very clever and witty thing to say. The answer, of course, is that there is (and that he's just an idiot). You just don't see other error codes very often, but then you don't see Peru very often. It doesn't mean it doesn't exist. So, without further ado, here's a list of all the possible http Status Codes:


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