404 error

404 File Not Found is a message that appears in most web browsers when a URL that leads to a page that does not exist on the web server addressed in the URL, leading to a "404 error."

The 404 error is one of the standard response codes of the web's HTTP protocol. The first 4 indicates a client error such as a mistyped URL. The middle 0 refers to a general syntax error. The last 4 just indicates the specific error in the group of 40x, which in this case is "URL Not Found". The use of three-digit codes is similar to the use of such codes in earlier protocols such as FTP and NNTP.

Note that a 404 error only occurs when the URL addresses a server that is actually running an HTTP server; otherwise, other messages are generated. These errors can be customized on a large number of such servers, such as Apache, to display a page that could be of more help than a default. Internet Explorer will not read these pages, however, unless they are larger than 512 bytes.

External links

• An example of a 404 error
• "Cannot find Weapons of Mass Destruction" 404 error screen parody
• 404 Research Labs
  Includes a gallery of custom 404 pages and information on how to create them.

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This article was originally based on material from the Free On-line Dictionary of Computing, used with permission. Update as needed.