A drive spins the disk very quickly underneath a read/write head, which does what its name says. It reads data from a disk and writes data to a disk. (A name that actually makes sense!)

Types of Magnetic Disks

Diskette / Floppy Disk

Sizes:

5¼"  (not used much now!)

3½" (starting to die out, too)

Both sizes are made of mylar with an oxide coating. The oxide provides the magnetic quality for the disk. The "floppy" part is what is inside the diskette covers - a very floppy piece of plastic (i.e. the mylar)

Other Removable Magnetic Media

Several other kinds of removable magnetic media are in use, such as the popular Zip disk. All of these have a much higher capacity than floppy disks. Some kinds of new computers come without a floppy disk drive at all.

Each type of media requires its own drive. The drives and disks are much more expensive than floppy drives and disks, but then, you are getting much larger capacities.

Hard Disks

These consist of 1 or more metal platters which are sealed inside a case. The metal is one which is magnetic. The hard disk is usually installed inside the computer's case, though there are removable and cartridge types, also.
 
Technically the hard drive is what controls the motion of the hard disks which contain the data. But most people use "hard disk" and "hard drive" interchangeably. They don't make that mistake for floppy disks and floppy drives. It is clearer with floppies that the drive and the disk are separate things.
 

There are other kinds of storage devices that are not magnetic, such as flash drives, or are not disks, such as magnetic tape. These will be discussed later.