As far as I know hard drives are more and more prone to have bad blocks as you travel back in time. An old man who had access to computers before I have even been born told me every HDD in production had some. However, nowadays as HDDs density went insane and each block is so tiny, a single bad block usually means a red alert suggesting more are coming and the whole drive is dying, nevertheless this is a rare thing to happen as we now can produce all the parts with extreme precision making it a "swiss clockwork" sort of reliable. This way, can't we produce a flawlessly perfect HDD of the old kind so its huge blocks would never turn bad?