Compressed Images

Compressed PS2 images: ZSO, CSO and CHD

Support depends on where the image is read and which program decompresses it.

Source and core	What to use
Local folder source or SMB, OPL core	ISO or ZSO; see the ZSO conversion instructions.
Local source, Neutrino core	Plain ISO. Neutrino does not decompress ZSO, CSO or CHD files itself.
UDPFS Files, Neutrino core	A compatible PC server can decompress CSO/ZSO/CHD and advertise a virtual .iso. The PS2 reads that ISO view.
UDPFS IMG / UDPBD	A served disk image containing the supported game layout; individual compressed-file serving is a UDPFS Files feature.

Trying a compressed game with PS2-Servers over UDPFS Files

1. Start with an ISO that already launches successfully, so the network and Neutrino configuration are known to work.
2. Place the compressed game under DVD/ or CD/ in the folder served by PS2-Servers, just as you would the original ISO. Keep its real .cso, .zso or .chd extension. Avoid a same-named ISO beside it: both would advertise the same virtual filename.
3. In Desktop/Core PS2-Servers, check Compression support. CSO is built in; ZSO needs LZ4 and CHD needs libchdr. The release bundles these optional libraries; the running build's support panel is the check that matters. Edge supports CSO and ZSO, with no CHD decoder.
4. Use UDPFS with Access: Files in RiptOPL. Refresh the game list after the server starts. A supported compressed image appears as an ISO because the server presents its decompressed contents to Neutrino.
5. Launch normally. If it is absent, first check the server's compression support and startup log. Renaming a compressed container to .iso does not convert it or enable support.

The files remain compressed on the PC; the server decompresses requested data before sending it. This saves PC storage, not network traffic. Compression can add PC CPU and random-read cost, so game performance still needs testing.

See PS2-Servers compression support and its optional dependency guide. Other UDPFS servers can have different capabilities. This guide does not add direct compressed-file decoding to RiptOPL or Neutrino.

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Source: docs/COMPRESSED-IMAGES.md @ b4c23bdac8f9.