This may be the oldest of all. When the hard drive stops being detected, some people tap it with a screwdriver or something similar during boot.

We have already seen this “procedure” done with an old hard drive, and it was recognized in one of the attempts. The disk worked for some more hours and then stopped for good.

We have received some disks with marks and dents on the outside, due to dozens of “taps”.

We can’t forget that distance between the read heads and the disk surface got shorter as time went by, and some modern disks (already discontinued – that’s lucky) used to let loose a part of the arm where we find the head parking and held it again when activated. It’s usual to find pieces of those heads spread inside disks whose user or technician used the “tap” solution. Those pieces scratch the disk in such a way that there’s no way to recover its data anymore. That’s why the “hit it” technique makes matters worse: before you could recover your data, but after having used it in disk of that type, the disk becomes totally irrecoverable.

This is what happens: if well applied, the taps can help to loose the read arm that has started to get stuck due to some failure in its circuit. They should be gentle, firm, and one at a time. If it doesn’t work after two attempts, you should stop. No brutality, because if the problem is not with the arm the taps won’t help at all, and if they were too hard they can even damage the disk surface.