I read about that 7x stuff back in the 80's. As I recall, it was based on the idea that you could look at the disk with an electron microscope or something and it could pick up echos of the previous data.
If this actually worked, data recovery companies would make a mint recovering overwritten files. But I've never heard of anyone advertising such or ever accomplishing it.
> data recovery companies would make a mint recovering overwritten files
Data companies make mint recovering deleted files and hard drives that have been disabled by the motor or control board just failing but recovering a full file from a hard drive with a microscope would be ridiculous.
If this actually worked, data recovery companies would make a mint recovering overwritten files. But I've never heard of anyone advertising such or ever accomplishing it.