Highly compressed PS2 games are ROMs/ISOs that have been reduced in file size while retaining the full gameplay experience. They are not "rip" versions (which remove cutscenes or music) but rather files subjected to advanced compression algorithms. The most popular format for AetherSX2 is .chd . Advantage: Smaller file size (often 40-60% smaller).
If you prefer .CSO files, you can use software like UltraISO. Open UltraISO on your PC and load your PS2 ISO. Choose from the tools menu. Select .CSO as your output format. aethersx2 games highly compressed
AetherSX2 supports several file formats that reduce the footprint of game data without sacrificing performance, provided the correct methods are used. CHD (Compressed Hunks of Data) Highly compressed PS2 games are ROMs/ISOs that have