3par OS location

As a complete Newpar Newbie, I have a simple question about the operating system of the storage system. Is the operating system in a 3PAR stored in its drivers or on disks as in some EMC models? When I have an empty 3par-Controller-Node: Can I add disks when the Controller-Node is licensed or do I need the HP preconfigured disks because the operating system is installed?
Thank you