(n.) The mechanism that
reads data from or
writes data to a magnetic
disk or
tape. If the head becomes dirty, it will not work properly. This is one of the first things to check if your
disk drive or
tape drive begins to malfunction.
The head is sometimes called a read/write head. Double-sided floppy disk drives have two heads, one for each side of the disk. Hard disk drives have many heads, usually two for each platter.
Also see What's Inside a Hard Drive? in the Did You Know . . . ? section of Webopedia.