IBM has another flavor of CAS which can be software-based, Tivoli Storage manager 5.3, or hardware-based, the IBM DR550. The architecture is different in that it is based on hierarchical storage management (HSM) design which provides some additional flexibility such as being able to support not only WORM disk but WORM tape and the migration of data from WORM disk to WORM tape and vice versa. This provides for additional flexibility in disaster recovery situations as well as the ability to reduce storage costs by moving data off the disk to tape.