Joomla CMS is using standard two different cache types for improving server response times :

• Global (core) cache for caching of selected parts (modules, component views, etc.) during rendering stage of request processing.

• Page cache dedicated to cache the entire web page for server output processing. In the plain CMS this function provides system plugin – System Cache.

In the following picture you can see same of major processing stages (prepare, render, finish) during Joomla CMS response processing and related cache activities in the case when JotCache plugin is used instead of System Cache plugin. Mostly render processing stage is very time consuming and for this stage is enabled Global core cache very helpfull.

But from the entire server response processing only a part of code (can be) is covered with global caching and therefore page caching which bypasses all the rest of output processing (as seen on next picture) for active (non-expired) cached web page can be in some multiple time faster as plain use of Global cache.