It is a "lossless" format, meaning the emulator reads it exactly like a full ISO. 2. CSO (Compressed ISO)
Under laws like the U.S. DMCA, circumventing copy protection (even for personal backup) is prohibited, though many jurisdictions permit personal backups of media you own. Distribution of compressed ISOs—even "full" ones—violates exclusive distribution rights.
Here are some tips for finding the best highly compressed PS2 ISO files:
(on PC) or mobile alternatives like AetherSX2/NetherSX2, you do not need to rely on sketchy third-party downloads. You can highly compress your own full-size ISO files losslessly. The primary supported formats include: CHD (Compressed Hunks of Data):