Why can’t we truly delete pictures and documents from a cellhpone or a computer ?


Not long ago I had to factory reset my computer because it had some problems. After the reset I managed to get my pictures and documents (I don’t remember if I recovered all of them) back using a recovery software. I even recovered pictures that were deleted prior to the reset.
Something similar happened with my cellphone.

Why is that ? Why can I get the pictures/documents back when they are supposed to be gone forever ?

In: Technology

Great question, the same thing just happened to me. A bunch of pictures from months, even a few years ago showed up in the transfer to the new phone… I don’t have an answer but am curious as well

Computer storage is designed to be stable for a long period of time. Some technologies, like flash memory, have a limited number of changes and a long storage life.

When you “delete” something, the storage is just marked as “unused”. Actually erasing it is bad for 2 reasons: a) it takes more time, and slow is annoying; and b) it might shorten the life of some storage.

When you fill the storage back up again, those storage blocks are filled with something new. Until then, they just sit there with their old information. Recovery programs read through this “unused” storage, looking for the patterns that define file structures it recognizes. When it finds storage blocks matching the pattern, it can restore, at least part, of the file.

You can get a “security erase” program that erases the blocks before it deletes the file, it’s just not the default behavior.

Deleting things normally doesn’t delete the data itself. It simply removes the index for it. If you imagine your memory is a library the books wouldnt be kicked out, they would just get removed from the catalogue. The space is declared to be free and can be used by anyone, but often you are lucky and the exact memory locations aren’t overwritten later.

If you try to get rid of data for good, things get more complicated. You can overwrite the former places of data with random numbers, but even then there will be hints left in the memory so a skilled person can recover some information. Even demagnetizing your harddrive isn’t completely secure. Harddrives with sensitive data are actually completely desintegrated to leave no clues behind.

You can fully delete documents from a computer, it just takes more time and effort then we’re normally interested in taking.

To create a file you need to write every byte of it to the HDD, SSD or SD card as well as create an entry in the file system (think of it like a hidden index file) saying where the file is and reporting that the area of the disk it’s in is now in use.

However to delete a file all we normally do is erase the entry in the file system. The contents of the file are still there (until something else overwrites them, since that area is no longer claimed) but as far as the OS is concerned the file is gone in an instant and the drive is ready to perform another operation.

You can get software that will ‘shred’ files by overwriting them completely with zeros before marking them as deleted, though this shredding process gets complicated with SSD storage due to wear leveling.

You can, it’s called zero filling. You basically overwrite the entire drive with zeros instead of the data that was there.