I guess those platters really do go 7200 rpm!!!
More about hard drives: A hard disk platter (or disk) is a component of a hard disk drive: it is the circular disk on which the magnetic data are stored. The rigid nature of the platters in a hard drive is what gives them their name (as opposed to the flexible materials which are used to make floppy disks). Hard drives typically have several platters which are mounted on the same spindle.
The magnetic surface of each platter is divided into small sub-micrometre-sized magnetic regions, each of which is used to represent a single binary unit of information.