iso's are container files. that means when it was made, they specified that it was to be 3gig big. but they only put 4mb in it before closing it, and they don't shrink to fit the files added. so it will always be 3gig big. iso's are like having cd/dvds on your hard drive. a dvd holds 4gig, but if you only put 10mb stuff on it, and close it, thats all you get, but the disk still has 4gig of storage capibilities.