If $db_prefix is "assumed to be a string", then does Drupal automatically sort what is a sharable table in the DB? $db_prefix = 'drupal_';


I've found many examples of installations which pick through the tables and place these in an array. And then there is the example of the site I am migrating where it only contained the above string. So, does Drupal sort it all out in the case of this simple string? 

What is the big idea I feel I am missing about multi-sites? 
(haha the mysteries of the D framework!)
$db_prefix can either be a string or an array, have a look at the documentation: Share a single database across multiple sites, the db_prefix_tables function take care of this job.