What is a Computer Hardware...?
A hard drive is nothing more than a magnetised storage area. Your Operating System is stored on your hard drive, as well as all your software programmes, like Microsoft Word. The hard drive is actually a few circular disks stacked one on top of the other. A little arm moves over the disks and writes things to these circular platters, and reads them.
What is an External Hard Drive...?
A hard disk drive is a data storage device used for storing and retrieving digital information using rapidly rotating disks coated with magnetic material.