One of the key features of the VTS is its capability to automatically use the 3590 and 3592 tape technology cartridge storage capacity. With a VTS, volumes being created by the host applications are stored in a tape volume cache built from DASD devices. The size of the tape volume cache is greater than the capacity of a native cartridge. The tape volume cache can potentially contain hundreds of tape volume images called virtual volumes, depending on the size of the volumes and tape volume cache. Through tape volume cache management policies, the VTS moves virtual volumes from the tape volume cache to a native cartridge managed by the VTS system. As virtual volumes are moved from the tape volume cache, they are stacked end to end on the cartridge and take up only the number of bytes written by the host, effectively using all of the storage capacity of the cartridge.