Why is permanently deleting a file without any trace of it left on the system is considered to be a really complicated process?

Question

I got the basics. Deleting a file simply tells the system that the sectors it occupied are now available for new data to be written on.

But if you want a more secure deleting why cannot you just overwrite everything with zeroes? If the computer system is only working at its core by manipulating zeroes and ones, why is it said that physically destroying the drive the information is stored on, is the only secure way to make sure nothing is left on it?

In: Technology

Answer 1

If you overwrite the file it is gone as fat as the computer is concerned.

However the physical medium itself might be different.

If you have magnetic media, a 1 written over a 0 may be distinguished from a 1 written over a 1.

In extreme cases it might even be possible to look back more than one write cycle.

This is mostly theoretical and would be hard to read out in practice, but to be sure there are standards that overwrite disks multiple times with multiple patterns.

Other media have different properties, but it seems restoring overwritten data is in theory always a possibility.

This is why degaussers and shredders built specifically for destroying tapes and disks exists.