Question about "expires" in http response

Hi,

I capture the following http request/response in Firefox tamper data
plugins.

My question is what does it mean ' Expires[Sat, 17 Jan 1981 8:00:00
GMT] '
in the http response? Does it mean it always expire? or it never
expire?



GET http://74.125.12.23/get_video?video_id=klQtI_rVeTM Load
Flags[LOAD_REPLACE ] Content Size[9306984] Mime Type[video/flv]
Request Headers:
Host[74.125.12.23]
User-Agent[Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.4)
Gecko/20070515 Firefox/2.0.0.4]
Accept[text/xml,application/xml,application/xhtml+xml,text/
html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5]
Accept-Language[en-us,en;q=0.5]
Accept-Encoding[gzip,deflate]
Accept-Charset[ISO-8859-1,utf-8;q=0.7,*;q=0.7]
Keep-Alive[300]
Connection[keep-alive]
Response Headers:
Pragma[no-cache]
Expires[Sat, 17 Jan 1981 8:00:00 GMT]
Cache-Control[no-store, no-cache, must-revalidate]
Content-Type[video/flv]
Content-Length[9306984]
Connection[close]

On Jul 9, 8:28 pm, "ying...@gmail.com" <ying...@gmail.com> wrote:

> My question is what does it mean ' Expires[Sat, 17 Jan 1981 8:00:00
> GMT] '
> in the http response? Does it mean it always expire? or it never
> expire?

It means that it has already expired and therefore should not be
cached.

DS