Um, ok, lemme explain, many games that were released in america on cartridges were only realeased in Japan on disks, or at least originally released for disks. These titles include zelda, zelda 2, castlevania, castlevania 2, metroid, kid icarus, mario 2 (jpn only), nazo no murasamejou (japan only). Games released on disk include save features which were sometimes removed in the american version. For example, you can save in the Japanese version of Metroid or Kid Icarus.