Oh, now i get it. The newer ones (SSFDR and SSCVR) is so much useful. Being able to last so long. I'm not too surprised thou that investigaters are able to retrieve data's that have been overwrite. It's just like what Blacksheep said, similar to retrieving data's from hard disk. Anyway thanks for the replies. At least now I understand more clearly how FDR's and CVR's works. I'm only a cabin crew aspiring to be a pilot. Trying to learn as much as possible.