Model 3420 -Tapes
3420 tape drives were introduced by IBM in 1970. The 3420 was a major technological advancement at the time. It was the first tape drive to have hardware assist instructions embedded within the tape drive. `By implementing for the first time a micro program in a read-only memory in the control unit, IBM engineers eliminated the need for a separate switching unit (previously, the IBM 2816) to permit more than one CPU to use the same drive. In addition, the 3420 made possible diagnostic testing of the unit from the controller without taking the tape unit offline.`*IBM withdrew the 3420 tape drives in 1987.
