HP Ultrium 3 WORM data cartridges will not allow any user data on the tape to be over-written. The drive is able to distinguish a WORM data cartridge from a RW data cartridge using two independent methods. WORM identity is encoded in the LTO-CM; this is different information to the RW tape. The WORM servocode is different. Both sets of information are written at the time of cartridge manufacture and ensure that a drive can never identify a WORM data cartridge as a RW data cartridge.