Bill’s back! And his subject this week may be the ultimate example of a truly astounding piece of engineering that we all tend to take for granted: The computer hard drive. A favorite college physics professor once admitted to me that the hard disk drive impressed him more than almost any other single piece of modern technology, and I have since found that, the more I think about it, the more I agree with him. As always, Bill Hammack does a great job of explaining things in a way that will appeal to both experts and amateurs. [Thanks, Bill!]