The primary reason to use CSO archives is to , allowing you to fit significantly more games on a single memory stick. ISO (Standard) CSO (Compressed) Size Large (Original UMD size) Small (Compressed up to 9 levels) Load Speed Fast (Direct read) Slower (CPU must decompress data) Compatibility Universal on all CFW High, but some heavy games may lag Portability Harder to share/download Easier due to smaller file size
To play these archived files, your PSP must be running , such as Pro-C or ME. This removes the UMD requirement, allowing games to run directly from the Memory Stick. How to Install and Play: cso psp archive
Dump your UMD using Custom Firmware on a PSP. Hold the R-trigger on boot to enter the Recovery Menu, enable "USB device: UMD," then plug into your PC. Copy the UMD.ISO file. The primary reason to use CSO archives is
A versatile tool for browsing and compressing PSP images. How to Install and Play: Dump your UMD
A 1:1 sector-by-sector copy of the original PSP UMD (Universal Media Disc). These files are uncompressed, fast to load, but take up massive amounts of storage (up to 1.8 GB per game).
If a game is laggy or has compatibility issues as a CSO, you can decompress it back to ISO: