There isn't really any such thing as "deleting" memory so that it becomes "empty". Individual memory locations can either be a 0 or a 1 at all times, there are no other options. You could write all zeros into the memory but that's still data. There is no way to "clear" a memory location such that it's neither a 0 nor a 1. That's why it's most efficient to delete a file by just freeing up those memory locations but not actually overwriting them, unless you're concerned about Russian spies getting your hard drive and restoring deleted data.