Gyroscopic Investing

I know that if you keep knocking your pc with your knee (or your desk with the pc on it), you're going to shorten its life. I guess this is because of the hard drive as that's the main moving part.

If laptops are also using traditional hard drives and not solid state ones, why is it that you can pick up a laptop and twirl it around, even when it's on, and not worry about killing the thing?

Do laptops use hard drives with extra stability built in, something that would make desktops too costly?

Or, maybe my initial premise is wrong (?)

I know that all (HDD) Mac laptops have Sudden Motions Sensors that auto-park the heads when it senses sudden movement.

http://en.wikipedia.org/wiki/Sudden_Motion_Sensor

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Other PC makers have similar systems. This is all known as Active hard drive protection.

http://en.wikipedia.org/wiki/Active_har ... protection

A number of laptop manufacturers have a feature like that.  In general, though, it's that laptop hard drives are designed to deal better with impact than desktop drives.  There are a number of ways that's done; the first one that comes to mind is that laptop drives are 2.5" in diameter versus 3.5" for desktop drives.  A physically bigger drive gives desktop drives more capacity and speed, but also magnifies the sensitivity to impact.  (Think of a 3.5" lever versus a 2.5" lever.)

Thank you both. Much appreciated!