I know that Apple advertises that feature, but I've never heard another manufacturer talk about it. Would my Compaq laptop have a motion sensor? It was the top-of-the-line model, but it's over a year old.

 

What Klaynos is talking about is a feature of the hard drive itself, not the computer. Apple and Compaq don't make hard drives, they buy them from hard drive manufacturers and install them into "their" computers.

My laptop has a transport lock. This prevents the disc spinning, and the head from moving off the landing zone. It can rest there safely, in contact with the disc, because there is now no relative motion except perhaps for a little vertical movement which is dampened by the head springs.