The operating system supports several IBM magnetic tape subsystems, such as the IBM 3480, the 3490 Magnetic Tape Subsystems, the 3590 High Performance Tape Subsystem, the IBM System Storage 3592 Tape Subsystem, as well as virtual tape, all of which use tape cartridges, instead of tape reels. For these subsystems, only a single density is available for reading and writing; any density specified with the DEN parameter is ignored.