magnetic disk

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A memory device, such as a floppy disk, a hard disk, or a removable cartridge, that is covered with a magnetic coating on which digital information is stored in the form of microscopic, magnetized regions.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (computer science) a memory device consisting of a flat disk covered with a magnetic coating on which information is stored