In the browser address bar press ENTER, F5, ctrl+f5 refresh the page difference

Enter in the URL address bar: Such a refresh, you can see in the Firebug, only a few requests will be sent out, and almost no picture of the request, this is because the request will first check whether the local cache of the requested picture, If there is a cache and there is no expiration (the expiration can be viewed through the header of the picture request), he will not issue the picture requests.

F5:f5 refresh is slightly slower than enter, for what, because he still sent all the requests to the server, but in the request header there is information

Expires	Fri, 28 Jun 2013 07:29:55 GMT
Last-modified	Mon, 21 Mar 2011 09:26:23 GMT

Server judgment has not expired, the direct return to 304not modified, in Firebug see is that these 304 requests are gray. Because it returns 304 of such information, rather than pictures, he is faster than ctrl+f5, but slower than enter, because he still sends out all the requests, which is slower than the non-request of Enter.

Ctrl+f5: This is going to be slow, all requests should be re-sent, re-read from the server, and no cache will read. In order to prevent the cache in the server to read, in the Ctrl+f5 refresh, the header of the request also added a special field, this can be used Firebug to see, it is very interesting. The Pragma:no-cache cache Control:no-cache will be added to the request header. These two are to tell the server to all the nodes in the middle of the browser, no cache, see this intermediate node also do not check their cache, ensure that the request is obtained from the server.

In the browser address bar press ENTER, F5, ctrl+f5 refresh the page difference