If-Modified-Since HTTP header: It means requested page hasn't been modified since the last request. Server should configured to return this response when a page hasn't changed since the last time requestor asked for it. It helps you to save your bandwidth and overhead because your server can tell to search engine spiders that a page hasn't changed. 301 Permanent Redirection: Use 301 Permanent redirection when you are moving your webpage or domain permanent to some other locations. It indicates search engine spiders that page is moved permanently to the new location. Use Server side redirection whenever you move your domain or webpage to new location. 302 Temporary Redirection: This redirection is similar to 301, but it indicates Search engine spiders to crawl the current page. It automatically forward requestor to the new location. 200 Status Code: This means server processed request successfully. For any file you are getting this response code means, the file is successfully accessible. But make sure your 404 (Not Found) pages should not return 200 status code OK. 404 (Not Found): Server is unable to process this request. In this case file is not present on the server.