When you think of the way that file removal is graphically presented, it’s easy to see how everyday users are convinced that the data is gone forever. However, digital trash much like real trash leaves traces behind and even if you take the trash out ready for the garbage collector, it’s still available for anyone to peek in on and snatch details of you from there. But they will need to act fast, otherwise the trash is taken care of and ultimately becomes mission impossible to recover any of the data thrown away.
What happens when I remove a file?
Imagine a huge library of books and reference materials: that’s your storage disk. As you save more and more data onto the disk, it’s like bringing more and more books into the library, filling it up. An index of the books sitting on the shelves is needed so that as the books flow in the catalog grows as well, indicating which book you will find on which shelf. In this metaphor, a book represents a ‘cluster’ for a storage disk.
When you delete a file you’re essentially marking that part of the shelf as free and updating the index to say that this book is no longer in your library. However, it doesn’t mean that the book has been taken off the shelf, so if someone happens to be around shortly after this update, the librarian (AKA the file system in this case) will still remember the old catalog and its content. This is what data recovery applications do when running a quick scan. But as time goes by the old books placed on these shelves marked as free are replaced by new books, reusing that original space – exactly as it happens on a storage disk too.
When data is deleted, it remains on the storage disk but is hidden from the user and the space it occupies is marked as free. Then, when the file system needs that space, it will put new data into that cluster, removing the existing data and lowering the likelihood of data recovery.
What happens when the file system overwrites data?
Operating systems and third-party apps offer the option to “secure delete” a file, which essentially means it will be put through a shredder, signaling the ultimate end of the data. Privacy-conscious people will choose to securely erase data from a computer in order to remove any trace of its existence. When choosing this option, the file system essentially runs an algorithm that overwrites the selected cluster several times, making it certain that data recovery is impossible. Overwriting replaces old data with new, but it doesn’t completely prevent data recovery. Deleting securely or overwriting a cluster multiple times erases every trace of the previously stored data.
István F.
Adam B.
