Re:how many... (Score 1)

There are usually two types of failures in hard-drives associated with external shock. One of which is the head going of track and writing to the wrong sector. This type of error can commonly occur if the laptop is accelerated (Less that 50-100m/s^2), perpendicular to the head arm. This is protected in a typical laptop drive by a shock sensor, that generates a write-inhibit signal if a shock in that range is detected. Some desktop drives also have this sensor (They reduce warranty returns on HDD failure while the computer moved around by the user to the "right place")

The second type of failure which IBM sensor protects against is something called "free fall". If a laptop falls off a desk. A zero-G signal is detected before the laptop hits the ground. This Zero-G signal indicating the free fall of the laptop is used to pre-emptively park the HDD head before the crash. This is the reason the HDD have to have a park time spec. Note that the shock sensor on the HDD cannot protect against such a shock.

BTW, these "free-fall" sensors are imperative for portable HDD applications.

How many people fried the drive on an iPod?