---------- Post added at 04:56 PM ---------- Previous post was at 04:53 PM ----------
No matter how overwritten a file is, as long as you have the right software, you can recover it, without losing the new files. The only way to "truly" delete files is to destroy the device or the drive.
---------- Post added at 09:18 PM ---------- Previous post was at 09:16 PM ----------
That is more than likely software related, if the files were already over-written then the software has to find a new location on the drive to place the files, which causes files to get fragmented, that might explain why the files are getting cropped. A simple defrag may solve the problem with the cropped files, if not, it may be that the software you are using simply is not powerful enough for this purpose.
Protip for IT technicians and Administrators: When deleting a file, all you are doing is rewriting the file with a binary code that is read by the computer as empty space on the drive. The code is simply an 8-bit binary string of 0's. So believe it or not, when you delete a file or folder you are really overwriting it directly. This is why I said above that no matter how overwritten it is, the file can still be recovered.
and it is almost impossible to fully delete all the information indeed, that is probably why microsoft doesn't give away used HDDs, they destroy it, but you can't recover ALL the information perfectly