Rapaire -

Sometimes, with sophisticated and expensive special equipment, it is possible to recover something that's been overwritten once or even twice, but many of the disk utilities include a "disk wiper" utility intended to prevent such recovery. The US Government considers anything that's been overwritten 6 times as generally not recoverable by any means available to foreign espionage agents. Their stuff is as good as ours. The typical "secure wipe" writes an 01010101... sequence followed by a 101010... followed by a 111111... followed by an 0000... to all "empty clusters." Two passes (8 overwrites) is considered "secure" but it's usually repeated 6x to meet the DoD "Tempest" secure wipe spec.

With the right equipment, damaged drives are fairly easily (not necessarily cheaply) recoverable, since the platters can be removed and mounted on a new shaft if needed. Most "drive failures" are because the motor quit, or the bearings failed. Alignment is pretty critical, but all that's really needed is to "make the disk(s) spin again." This is the "bread and butter" business for the data recovery guys. Some of them may pull up something that's "once overwritten" if you can tell them what they're looking for, but it would have to be a "matter of national security" to be worth going further than that.

Older drives often suffered "disk collisions" where the read/write head hits the surface of the disk and plows furrows in it. So far as I know, no one has found a way to "unfurrow" this kind of failure, when the disk surface is damaged. Sometimes a "collision" only misaligns the heads, and then a recovery service can just "bend them back" and read the disk. This kind of failure is extremely rare in "modern" drives (floppies and ZIP drives excepted, where it's still far too common).

Do we need to say "Backup your data?"

John