Ironically, the best way to understand recovery is to understand how to prevent it. To definitively erase a disk before selling it, a simple format is not enough.
You must perform a Wipe or Zero-fill: writing zeros to every sector of the disk. On SSDs, using the manufacturer's Secure Erase function is the only way to purge all NAND cells, including the over-provisioning areas that the operating system cannot see.
