"404 Not Found" is an important part of the Internet itself, so that it has become a cultural phenomenon, many Internet Co will produce their own exquisite "404 pages", help you reduce the number of pages can not access the frustration.
"South Park" website 404 page
so, 404 in many cases has become synonymous with "(stations) can not access, such as some people ridicule Google executive chairman Eric · Schmidt’s visit to North Korea:" North Korean officials met with 404 Not Found site leader".
however, the bottom up, this sentence is wrong. 404 is actually a HTTP status code state code, usually on behalf of the page you visit has been moved or deleted. In the context of the previous paragraph, in fact, because of the North Korean government relations, it led to Google can not access.
now, the Internet Engineering Steering Group to develop the Internet technology standard (IESG) by a new code: 451, is the case for legal reasons, meaning "based on, I can’t show you to the web page content". IESG Mark Nottingham introduction, 451 is to deal with an increasing number of Internet censorship.
‘s current Internet censorship is divided into several categories, one of which is a review of political content, such as North Korea and Iran, as well as a review of the European piracy sites like the pirate bay. With 451 code, browse this can also be a better understanding of what causes the page error.
of course, like the 404 code, the site manager can set the personality of the page, you can also choose not to display the code. 451 is a brand new, not yet known error code, in some countries, the government’s requirements or self censorship site, the 451 code is likely not to be displayed.
"it is conceivable that some governments will avoid this transparency: not only to prohibit access to certain resources, but also to deny the existence of censorship." One of the authors of the XML standard Tim Bray so predicted.