in reply to Ways of caching

The approaches you mention will help reduce server load by reducing the frequency with which you need to regenerate pages.

When serving information over HTTP, you can reduce server load further by allowing Web caches to serve previous versions of unchanged content. It's possible to make pages cacheable, yet ensure that caches won't serve stale information by using HTTP's If-Modified-Since header field.

See the Caching Tutorial for Web Authors and Webmasters for detailed information.