This got rarer later on, once they realised the could fill the discs with FMV sequences instead.
Speaking of PS1 games and disk-filling FMVs: Final Fantasy 7 on the PSX comes on 3 disks but the actual game itself is duplicated on all of them and you can swap them out during gameplay, and the only thing that happens is that it plays the wrong FMVs.
It all breaks down to the actual “game” taking 133MB, plus few hundred for the uncompressed pre-rendered backgrounds, out of the available ~1.8GB (according to this old post about how a Nintendo DS port could easily fit on a 256MB flash cart.)
Speaking of PS1 games and disk-filling FMVs: Final Fantasy 7 on the PSX comes on 3 disks but the actual game itself is duplicated on all of them and you can swap them out during gameplay, and the only thing that happens is that it plays the wrong FMVs.
It all breaks down to the actual “game” taking 133MB, plus few hundred for the uncompressed pre-rendered backgrounds, out of the available ~1.8GB (according to this old post about how a Nintendo DS port could easily fit on a 256MB flash cart.)