HTTP 404 Error Page

Internet Explorer (before Internet Explorer 7), however, will not display custom pages unless they are larger than 512 bytes, opting to instead display a "friendly" error page. Google Chrome includes similar functionality, where the 404 is replaced with alternative suggestions generated by Google algorithms, if the page is under 512 bytes in size.
Some websites report a "not found" error by returning a standard web page with a "200 OK" response code; this is known as a st 404. St 404s are problematic for automated methods discovering whether a link is broken. Some search engines, like Yahoo, use automated processes to detect st 404s. St 404s can occur as a result configuration errors when using certain HTTP server stware, for example with the Apache stware, when an Error Document 404 (specified in a .htaccess file) is specified as an absolute path (e.g. http://example.com/error.html) rather than a relative path (/error.html).
Some proxy servers generate a 404 error when the remote host is not present, rather than returning the correct 500-range code when errors such as hostname resolution failures or refused TCP connections prevent the proxy server from satisfying the request. This can confuse programs that expect and act on specific responses, as they can no longer easily distinguish between an absent web server and a missing web page on a web server that is present.