Magnetic tape controller
A magnetic tape controller is the term for the electronics which connect magnetic tape drive(s) to a computer.
Exactly what functionality is included all depends on the manufacturer, and often on the particular product line, though; how they paritition functionality, and how they pull out common sub-units to prevent un-needed duplication.
One common variant is the division of the controller functionality into a unit which is the actual interface to the computer, and another, the formatter, which understands how to talk to the drive(s), and write standard formatted tapes.
An example of the single controller organization is the DEC TU10/TM11 system; the DEC MASSBUS system of a MASSBUS interface, TM02 formatter, and tape drives, is an example of a separate formatter and bus interface.