Why does deleted data stay on a HDD once written, waiting to be overwritten, as opposed to being removed when requesting deletion?

Question

Why does deleted data stay on a HDD once written, waiting to be overwritten, as opposed to being removed when requesting deletion?

In: 22

Answer 1

Think of a hard drive like a book with millions of pages (sectors).

You could go to each page and erase the text off it, however this takes a lot of time and adds wear to the pages. Often, the data won’t even be on pages next to each other, requiring you to jump around the book to find all the pages.

Or, you can just go into the index and erase the entry and figure nobody will look at the pages or be able to figure out the correct pattern.

There are “secure delete” tools that will do the former, but such functionality is not normally needed, and the extra cost is not worth it.

With actual HDDs, there is also leakage of the data slightly outside of where it’s supposed to be, which can sometimes be used to recover even overwritten data.