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

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, described below. It is clearer with floppies that the drive and the disk are separate things.

Diskette / Floppy Disk

Sizes:

5¼"  (really old stuff)

3½" (pretty much gone now)

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).

These disks are rapidly vanished. New computers often come without a floppy disk drive at all unless you ask for one.

Other Removable Magnetic Media

Several other kinds of removable magnetic media are in use, such as the Zip disk. All of these have a much higher capacity than floppy disks.

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.

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.