An external label is required for every tape cartridge in the tape library. This label contains both machine-readable and operator-readable identification characters that are used by the tape library's vision system to identify the volume serial number of the cartridge. In a manual tape library, a machine readable external label is not required, but is advisable for migration purposes.

The external label must be applied within the indentation on the side of the cartridge; however, a larger information label, supplied by the customer, can be used on the top of the cartridge.