(Compressed ISO) file is a compressed version of a standard (PlayStation Portable) game disc image
Introduction: Decoding the Keyword
While CSO is great for space, it isn't always perfect. Because the PSP has to decompress the data while you play, you might experience: cso psp archive full
ciso_compress -z9 input.iso output.cso
Playing on PC: Emulators like PPSSPP handle CSO files natively. You do not need to unzip them; simply load the .cso file as you would an ISO. PPSSPP is efficient enough that the performance hit from compression is often negligible on modern hardware.
Playing on PSP Hardware: To run a CSO archive on actual hardware, you generally need Custom Firmware (CFW). The PSP’s native firmware does not support loading games from the memory stick without official purchasing mechanisms (like the now-defunct PSN store).