Popular for handhelds and some homebrew. Software like MaxCSO is specifically designed for PS2 games and is compatible with various loaders.
Many PS2 discs contain over 1 GB of empty padding. Removing this can shrink a 4.3 GB ISO down to 1.5 GB or less without impacting the game's quality. How to Compress and Use PS2 ISOs ps2 highly compressed games iso
A standard ISO file is a sector-by-sector copy of a physical disc, including the file system and "padding"—empty data (often just zeros) used by developers to fill the disc and improve reading speeds on original hardware. "Highly compressed" versions use various methods to eliminate this excess: Popular for handhelds and some homebrew