title: Difference between user and system caches using PHP APC
body: <p><a href="http://php.net/apc_clear_cache" rel="nofollow noreferrer"><code>apc_clear_cache</code></a> has an option to send in 'user' which will delete the apc user cache, or else if not present, the system cache.</p>
  
  <p>I don't understand the difference since there's no way to explicitly store a value in one cache over the other via <code>apc_store</code>/<code>apc_fetch</code>.</p>