The Galaga Famicom Disk System version could only be obtained via the Disk Writer method where you bought an empty disk and could copy a game for a small fee at certain copy stations/kiosks. The game is identical to the cartridge version with the exception of different copyright dates on the title screen. In the five years that lay between the cartridge and disk versions much happened in the video game industry. Sure, the disk version was much cheaper and the gameplay has the same classic feel to it but in 1990 this game already must have been mostly played out of nostalgic feelings I would guess.