Authcache is drupal community contributed module you can find here Authcache project page. The Authcache module offers page caching for both anonymous users and logged-in authenticated users. This allows Drupal/PHP to only spend 1-2 milliseconds serving pages, greatly reducing server resources. Please note that enabling authenticated user caching will require modifying how your user-customized content displays on your pages. You should be an experienced Drupal developer if you choose to implement the full functionality of this module. Anonymous caching won't require any changes and will offer a speed improvement over Drupal core since hitting the database can be completely avoided.
To install authcache module you need
- Download authcache module and extract it to drupal contrib modules dir (usual /sites/all/modules).