Content expiration

Microsoft IIS uses the Expire Web content header (located in common HTTP Response Headers) to determine whether to return a new version of the requested web page if the request is made after the web page content has expired. IIS marks each web page before it is sent, using the settings that you provide for content expiration. The website visitor's browser translates the expiration mark. You can set the IIS Expire Web content header to improve performance.

By setting Expire Web content to something other than immediately, you can reduce second-access load times by 50 –70%. This setting does not affect dynamically-generated content.

For more information about content expiration, see Client Cache in the Microsoft IIS documentation.