caching question

I am using Apache 1.3.27 and PHP 4.3.3.RC1 and someone has told me that my web page cannot be cached but I cannot figure out why. My friend tells me my pages all keep sending this in their headers: Cache-Control: post-check=0, must-revalidate, no-store, no-cache, pre-check=0 But I can't figure out why the headers are set like this. I am not setting any headers so I am wondering if it is a setting in my web server, php.ini file or some other php scripts I have running in the background. Also print_r($HTTP_SERVER_VARS) gives one server variable to be: [HTTP_CACHE_CONTROL] => max-age=0 What does this variable mean and where was it set? Any and all help appreciated! Jean-Christian Imbeault