A real tape drive attached to your VM at a virtual address will have the tape mounted
on it rewound to the load point ready for reading from the start of the volume.
vaddr a virtual device address of the form cuu
REWIND NOT PERFORMED is given is the tape drive is not ready or as sometimes happens
the tape runs off the take-up reel due to a too short leader.
REWIND COMPLETE the tape is rewound and ready to be read from.