Why does freezing your hard drive sometimes help to recover data (technical details)?

Solution 1:

I cannot cite source but in some IBM training a number of years ago, the instructor mentioned that there was also an effect of the metal parts moving as they became cold. A platter then might be in a slightly different position and be readable. The cold might also free a stuck spindle as the spindle and bearing contract differently. It may also change the position of the heads on the platter.

Solution 2:

Cold can have an effect on magnetism, because cold can have an effect of how fast charged particles move. It is the motion of charged particles, usually electrons around a nucleus, that produces magnetic fields. Cooling a metal can make the motion within less random, thus allowing more atoms to line up with each other. This increases the magnetic field of the material. On the other hand, making a magnet very hot will cause more random motion, resulting in less allignment of molecules and less megnetism.

Source

This means colling the HD can restore some particles to the right state so the header will have less problems reading the data of that sector.

Solution 3:

My understanding is that it was a matter of differential thermal expansion. The cold drive will have things in a slightly different position relative to each other than the warm drive. This is especially useful if the fault was a stuck bearing keeping it from spinning up, although I have heard this is no longer normally an issue. I've never actually had a case to try it.