Compressing to ZSO (Recommended for Console Compatibility)
Use maxcso to compress raw DVD ISOs into high-speed ZSO images:
maxcso --format=zso --block=2048 game.iso -o DVD/SLUS_201.74.Game.zsoCompressed Disc Formats
PS2 Servers supports compressed disc formats, enabling you to store large game libraries in a fraction of the disk space while streaming them seamlessly to your PlayStation 2.
Server-Side vs Client-Side Decompression
There are two ways compressed images are streamed:
- Client-Side Decoding (ZSO): The server transfers compressed LZ4 blocks directly over the network; the PS2's processor decompresses them in RAM. This minimizes network traffic.
- Server-Side Decoding (CHD & CSO): The host PC or router decompresses requested sectors in real time and delivers raw optical disc sectors to the console. The console never knows the file is compressed.
1. Format Comparison Matrix
| Format | Algorithm | Typical Storage Reduction | Console Decoding | Server Decoding Support |
|---|---|---|---|---|
Raw ISO (.iso) |
None (Uncompressed) | 0% | Native | Desktop · Core · Edge |
ZSO (.zso, .ziso) |
LZ4 (2048-byte blocks) | 20% – 45% | Native in OPL / RiptOPL | Desktop · Core · Edge |
CSO (.cso, .ciso) |
Deflate / zlib | 25% – 50% | Limited / High IOP load | Desktop · Core · Edge |
CHD (.chd) |
LZMA / FLAC / zlib | 35% – 65% (Best) | None | Desktop · Core (via libchdr) |
2. Optional Compression Dependencies
PS2 Servers Desktop and Core automatically inspect the Python environment for optional acceleration and decompression modules:
libchdr— Required for CHD format decompression. Included in pre-compiled Desktop packages; installable viapip install libchdrin source mode.lz4— Accelerates ZSO block parsing and verification.zstandard— Provides Zstandard dictionary acceleration.
Desktop Dependency Panel
In PS2 Servers Desktop, click Settings → Dependencies to inspect the detected status of all optional compression libraries. If a library is missing, Desktop displays exact installation commands for your OS.
3. Compressing Your Disc Images
Compressing to CHD (Best Compression Ratio)
Use chdman (from the MAME toolset) to achieve maximum compression for Desktop/Core serving:
# For DVD games:
chdman createdvd -i game.iso -o DVD/SLUS_201.74.Game.chd
# For CD games (from CUE/BIN):
chdman createcd -i game.cue -o CD/SLUS_201.74.Game.chd