Why is the movie data larger than a DVD-R?

I have no problem making a backup of a movie, compressing it and whatever, PC and Mac, but why does it need to be compressed? Didn’t the movie come off a DVD? Shouldn’t it fit back on, especially since CSS is removed? That should make it smaller! Are movies on dual layer DVD’s? If so, why can we play them, when the average burner can’t make them?

Your Definately New to the Game - Welcome! Genuine DVD Originals are stamped as opposed to burnt by a million dollar machine called a Glass Master. These Stamped Discs are generally equivalent to a dual layer DVD = 8.5Gig or so, but the movie itself is usually only around the 5-6Gig mark. Add in Extras credits and Audio Streams youve got maybe 7Gig. So when you use a 4.7Gig (4.38Gig) Single Layer Disc Compression is necessary to make it fit. Removal of CSS Protection will make little if no difference to the size.