| Format | Compression Algorithm | Typical Compression Ratio | Best Use Case | Decompression Speed | | :--- | :--- | :--- | :--- | :--- | | | None (Raw) | 0% | Archiving, compatibility | N/A (No decompression) | | CSO | DEFLATE | 40–60% | Older PSP emulators, maximum space saving | Slow to Medium | | ZSO | LZ4 | 30–50% | OPL, PS2/PSP emulators, performance‑sensitive devices | Extremely Fast | | CHD | LZMA / FLAC | 50–70% | Modern emulators (MAME, Dolphin), archiving | Slow (Higher CPU usage) |
Optimize (if needed):
This is the most obvious advantage. A standard PS2 DVD ISO is often 4.7GB in size. When converted to ZSO, that same game can shrink by . If your storage medium (external HDD, flash drive, internal SSD) is limited, converting your library to ZSO can more than double the number of games you can store on the same drive. This is a life‑saver for those using large HDDs in their old consoles. iso to zso converter