Thomas Hambach

An interesting resource about what those Cache Control headers actually mean! Sure made things a lot more clear for me!

Internet Explorer applies the following logic to objects served with these extensions:

1. Upon first request, the object is cached and is served from cache until the post-check interval expires.
2. Once the post-check interval expires IE fetches the object from cache and checks for an updated one in the background. If a newer object is available it caches it. Upon every subsequent request this updated (and now cached) object is served until the pre-check interval expires.
3. Once the pre-check interval elapses the object is treated as expired. IE will first ask the HTTP server if the object has changed since it was requested by the browser. If it has, IE will load the updated object.

read full article: http://aspnetresources.com/blog/cache_control_extensions.aspx