i have two 750 Gb internal hard drives. recently had a problem with one so i opened on my backup and erased the first, twice, then cloned it. everything seemed to go great, booted back up on the first, checked permissions and all was good. now im doing a software update, itunes, imovie, and system update, taking a few hours, and so on, but i now notice the my bootup hd is showing almost 100 gb more on it than the one i cloned from. how can a update add 100 gb.