Digging Deeper into Drupal Page Caching

Brian Osborne has a very informative article on the Drupal page cache:

... I wanted to provide a more comprehensive look at Drupal's core caching, explaining how some of this stuff is actually working under the hood. ...

Page caching is when Drupal takes the entire rendered output of a page request and stores it in the Database (or another cache store, defaults to DB). Cached pages only apply to anonymous traffic - meaning users that are not logged in and do not have any "session" data (like a product added to a shopping cart). Since the page is rendered once and stored in its entirety in the cache, there is no opportunity to change the content. Dynamic content for logged in users like a simple welcome message, or a list of items in a shopping cart, can't work in tandem with Drupal's built in page caching.