The Collaborative International Dictionary of English v.0.48:

magnetic disc \magnetic disc\, magnetic disk \magnetic disk\n.
   A ditical memory device consisting of a flat disk covered
   with a magnetic coating on which information is stored; a
   hard disk, floppy disk, and diskette are typically
   magnetic disks.

   Syn: disk, disc.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

magnetic disc
    n 1: (computer science) a memory device consisting of a flat
         disk covered with a magnetic coating on which information
         is stored [syn: magnetic disk, magnetic disc, disk,
         disc]