MVS first honors the device type that DFSMShsm selects. If DFSMShsm specifies a generic unit name for a cartridge-type device, MVS allocates a cartridge-type device, but selects a cartridge-type device with or without a cartridge loader according to its own criteria. (If all the devices have cartridge loaders, the MVS criteria are unimportant.) If DFSMShsm specifies an esoteric unit name that is associated with devices with the cartridge loader, MVS allocates a device from that esoteric group.

If the DFSMShsm tape-allocation request is for a cartridge-type device, MVS selects a device by considering whether the request is for a specific tape or for a scratch tape. If the request is for a specific tape, MVS tries to allocate a device that does not have a cartridge loader. If the request is for a scratch tape, MVS tries to allocate a device that does have a cartridge loader. If the preferred kind of device is not available, MVS selects any available cartridge-type device.