well dvd-rom is just a typical disk drive, the ram thing was something started by I believe Panasonic, but I don't really remember right now. ANyways, it came out with the whole +-r/rw thing, Panasonic claimed it could be rewritten like 250,000 times or something crazy, I guess they kinda wanted to pass it off as like an extention to your hard drive or something, but to answer your question simply, it's just another form of dvd rewritable, one that really didn't take off very well