What is 404
 

404 is a HTTP error code, namely request page does not exist. Code 404 first "4" on behalf of the client error, such as error page address; Two digital code represents a specific error message. 404 page is when the user input the wrong link or visit a does not exist address, to return to the page. The object is to show visitors the requested page does not exist or link error, and at the same time, guide the user's use of the site other pages rather than close window to leave.

Search engine via the HTTP status code to identify the state of the web page. When the search engines get a link error, the site should return a 404 status code to tell the search engine to give up the index of the link. If it returns a status code of 200 or 302, the search engine for the link index, which leads to a large number of different links pointing to the same web content. A result, the search engine significantly reduce trust this site. - Many sites exist: 404 pages return a status code of 200 or 302 instead of a 404 status code.