I think you will like this short video. If you have ever wondered what, exactly, was making that clicking noise when your computer was reading it's hard drive, now you will know.
Keep in mind, while you watch this, that the disk is probably rotating about 120 revolutions every second. It really is kind of amazing that the read head can locate and read data at such speed. Equally amazing that these drives are now manufacured at such low cost. Half a terabyte now around $150.