It depends on how a drive is formatted. Considering Windows, prior to Windows Vista, using either a Quick or Full format did not alter the stored data on the drive. The Quick format rebuilt the filesystem metadata files to represent the drive as empty, with all the data area of the formatted volume marked as available for storage. The Full format also did an integrity check of the volume, reading all sectors and performing a Cyclic Redundancy Check. In both cases the original contents of the data area remains intact, and can potentially be recovered as files by recovery software. As new data is written to the drive, it progressively overwrites these locations, and where overwritten, if recovery software "recovered" those locations, the contents of a previous file that was there will no longer be there. What is there now would be "recovered".
From Windows Vista onward, Quick format works the same, but a Full format will zero fill the user area of the volume being formatted. Because every sector of the formatted volume is overwritten, again the data that was previously there has been replaced, and software, including manually operated software like hex editors, can only return nulls from these locations. This will achieve basically the same results as filling the drive with alternative files.
However under laboratory conditions with the right equipment and techniques, it can be possible for the remnants of prior data on the drive to be seen, but it is not an easy thing to do by any means, and is a very costly process. So for many applications, a zero fill, either from a Full format or a third party wiping utility, is adequate since no-one will take those measures with a random old hard drive.
If someone wants a high degree of certainty that laboratory recovery will not succeed, apart from physically destroying the drive it can be put through a degausser, or given multiple pass wipes. Even though multiple pass wiping was developed for older drive types and may no longer deliver predictable results with modern ones, an organization that has to comply with regulations may still need to perform a particular standard of multi pass wipe.
Edited by Platypus, 22 July 2017 - 10:08 AM.