What is a disk drive?

Answer 1

Your computer doesn't really remember anything after you turn it off, with the exception of a few basic settings stored in a specialized "non-volatile" memory location called "bios". All of your high speed memory forgets everything as soon as you turn off the computer.

And yet...

We seem to want our computer to be able to remember things, lots of things, such as how to perform some of the basic tasks that we use every day (programs), data that we want to be able to get to later, (pictures, songs, financial information, documents)... but if the computer memory forgets everything every time we turn off the computer, how can we get it to remember all of that stuff? Enter - the disk drive.

The disk drive has one or more "platters" which spin at a high speed and one or more "read/write heads" which move across the surface of the platter. The disk drive reserves certain locations to tell the computer where the "good stuff" is, and when the computer starts up it loads that information into volatile memory. Then, whenever you want to read something the computer tells the disk drive to move it's head to a certain location and start reading. Alternatively, the computer can tell the disk drive to start writing, just in case you want to change something or save something new. Next time you turn off the computer, the information will be stored on the "disk drive", and you should be able to read your information... providing that everything is working properly. Of course, this is all a masive oversimplification of the way it's implemented, but it's a reasonably accurate description.