| Method | How it works | Typical size reduction | Lossy/Lossless |
|--------|--------------|------------------------|----------------|
| Generic archiving (7z, ZIP, RAR) | LZMA, Deflate, PPMd | 30–60% | Lossless |
| CSO (CISO) | Compresses ISO by recompressing sectors (zlib) | 40–70% | Lossless |
| CHD (CloneCD) | Huffman + LZMA, used in MAME | 50–85% | Lossless |
| RVZ (Dolphin/PCSX2) | Custom, strips junk + compression | 50–90% | Lossless (optional junk removal) |
| ZSO (Zstandard ISO) | Zstd compression per sector | 50–80% | Lossless |
| Dummy file removal | Replaces padding (e.g., DUMMY.DAT) with zeros → recompress | 10–30% extra | Lossless (no game impact) |
| Audio/video re-encoding | Convert CDDA to OGG, FMV to H.264 | 60–95% | Lossy (breaks some games) |
Key note: True “high compression” for emulation usually means CHD or RVZ + dummy removal. Lossy methods are not recommended for preservation. ps2 iso files highly compressed full
Use 7-Zip (free) or WinRAR to extract the archive. Inside, you will find one of three formats: | Method | How it works | Typical
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. Key note: True “high compression” for emulation usually