It should read off of CD as an additional Runtime file, but beware if you do any grouping, or try to save to the external Runtime. I back mine up onto CD, then dump it back onto HDD when needed. CD transfer speeds are still a touch slower than native HDD speeds (at least on my SCSI box it is), though an external firewire drive is real nice for storing an external Runtime, becuase your transfer speeds are equal to internal HDD speeds, and it can be written to. /P