The cache system, which you can turn on at Admin Panel -> Settings -> General, allows your pages to load faster, by caching a copy of what the page looks like to each usergroup. This means that you should only use the cache if there's a single way you want each page to look to all members of each group -- if you have multiple template sets or multiple languages you want to let people choose among, you will not want to use the cache.

Caching is often a good idea for guests, and usually harmless for administrators, but not so ideal for other groups. For registered member usergroups you can use the cache only if:

• You don't care that the 'edit' buttons by links are deactivated for non-admins.
  
• You don't care that the 'edit' buttons by comments are visible on all posts (though they give a no permission message as appropriate when clicked).
  
• You have PMs off or don't care that the number of new PMs cannot be shown properly.
  
• You don't care that any member template variables you use in places like the 'main index' or 'show links in category' templates will become generic to each usergroup. Note that the member home area is excluded from caching, so members will still be able to view a list of their links for editing and the like there.
  
• You don't use secondary usergroups.
  

By default the cache updates pages randomly an average of once every 20 views -- for sites with fewer views you may want to change 20 to a lower value. After submissions are made it automatically updates the cache of the destination page. Please note that the cache can use up huge amounts of disk space on a large site. If you have 500 categories and 15,000 links, it could take a gigabyte to fully cache. The total cache size will be bytes-per-page * number-of-pages * number-of-usergroups-cached. If your space is limited you can set a limit on the total size in your cache settings, but the smaller you make this value the more often slow uncached pages will be served.

After making template changes or the like you may wish to reset the cache, by clicking the "empty cache now" link at Admin -> Settings -> General.

The cache system excludes the admin panel, plus anything under these files on the user-side: edit.php profile.php privatemessaging.php buddylist.php online.php 2checkout.php paypal.php nochex.php activate.php upgrade.php setup.php attachimport.php chat.php im.php in.php modcp.php newposts.php savedtopics.php searchips.php securityimage.php revisepost.php addpoll.php invites.php