There are four options under Check for newer versions of stored pages:
Every visit to the page: When you return to a page you viewed previously, Internet Explorer should check to see whether the page changed since you last viewed it. If the page has changed, Internet Explorer displays the new page and stores it in the Temporary Internet Files. Note that selecting this option can slow down browsing between pages you have already viewed.
Every time you start Internet Explorer: When you view a Web site that you have visited before in the same Internet Explorer session, Internet Explorer uses the cached temporary Internet files instead of downloading the page. If you press F5 or click Refresh, Internet Explorer downloads the page.
Automatically (Internet Explorer 5 and later only): This is the same as the previous setting, but with a logic algorithm to understand the habits of Web page behavior. This setting specifies that when you return to a page you viewed previously, Internet Explorer should not check to see whether the page has changed since you last viewed it.
If you select this setting, Internet Explorer checks for new content only when you return to a page that you viewed in an earlier session of Internet Explorer or on an earlier day. Over time, if Internet Explorer determines that images on the page are changing infrequently, it checks for newer images even less frequently.
Never: Internet Explorer does not check the Web server for newer content.