The native file format for a PSP game is an (a bit-for-bit copy of the UMD disc). A typical ISO can range from 100MB to 1.8GB. "High compression" usually refers to converting that ISO into a CSO (Compressed ISO).
(~15 MB): A deep, classic action RPG that originally started as a mobile hit. Pac-Man Championship Edition psp highly compressed games under 50mb
: A classic city-building simulation ported to the platform, taking up approximately . Spongebob SquarePants: Super Sponge The native file format for a PSP game