WordNet (r) 3.0 (2006):

disk controller
    n 1: (computer science) a circuit or chip that translates
         commands into a form that can control a hard disk drive

The Free On-line Dictionary of Computing (30 December 2018):

disk controller

    (Or "hard disk controller", HDC) The
   circuit which allows the CPU to communicate with a hard
   disk, floppy disk or other kind of disk drive.

   The most common disk controllers in use are IDE and SCSI
   controllers.  Most home personal computers use IDE
   controllers.  High end PCs, workstations and network file
   servers mostly have SCSI adaptors.

   (1998-03-16)