Compressed ISO disc image commonly used for PlayStation Portable games and software
File type: Archive and compressed file
CSO, also called CISO, is a compressed ISO disc image format. It stores an optical-disc image in compressed blocks to reduce file size while preserving the structure and data of the original ISO.
CSO files are most commonly used for Sony PlayStation Portable (PSP) game and software images. They can be opened by PPSSPP and other CISO-compatible software; original PSP hardware generally requires compatible custom firmware to load them.
Found 2 different file type records with the same cso filename suffix.
File type category:
Archive and compressed file
Date updated: August 2, 2026
A CSO image is produced by compressing the data blocks of an ISO image. The format uses an index to record each block's location and whether it is compressed, allowing compatible applications to read the image without fully decompressing it first. Empty or zero-filled blocks can be stored particularly efficiently.
The format became popular in the PSP community as a way to reduce the storage space required for images of Universal Media Disc (UMD) software. Classic CSO tools commonly provide nine compression levels: higher levels may create smaller files but can require more processing and sometimes result in slower loading.
PPSSPP supports CSO images on Windows, macOS, Linux, Android and other supported platforms. Command-line utilities such as maxcso and ciso, as well as PSP ISO Compressor, can compress, decompress and convert compatible images.
CSO is a disc-image format rather than a general-purpose archive such as ZIP or 7Z. Browsing, mounting or emulating it requires software with CISO support, and images should be used only when the user has the appropriate rights to the underlying software.
On Windows, macOS or Linux, install PPSSPP and select the CSO image through its file browser or game-opening function. The application can usually load the image directly for PSP emulation.
For inspection or decompression, use a compatible build of maxcso, ciso or PSP ISO Compressor. Original PSP hardware generally needs compatible user-installed custom firmware. If an application does not recognize the image, convert it to ISO rather than merely renaming the extension.
To convert CSO to ISO, use maxcso, ciso or PSP ISO Compressor and choose the decompression or ISO output option. To convert ISO to CSO, use one of these utilities and select a compression level; lower levels generally favor access speed, while higher levels usually produce smaller files.
Dedicated desktop tools are preferable for large disc images. Online conversion services for CSO are uncommon, may impose file-size limits and can create privacy or copyright concerns when images are uploaded. Test the converted image in PPSSPP or another CISO-compatible application.
Software applications that can open cso files:
Apps designed for playing cso files:
Multiplatform
Software apps that create cso files:
Microsoft Windows
Apple macOS / Mac OS X
Prometeus
Software apps that convert cso files:
Microsoft Windows
Apple macOS / Mac OS X
Prometeus
Multiplatform
Software apps that import cso files:
Microsoft Windows
Software apps that extract cso files:
Microsoft Windows
Apple macOS / Mac OS X
Prometeus
For those who never owned Sony PlayStation Portable console and yet want to experience all those gre...
File type category:
3d graphics, CAD-CAM-CAE file
Date updated: September 9, 2024
The cso file extension is related to the Compiled Shader Object format. CSO is compiled object, written in High Level Shader Language (hlsl file extension), developed by Microsoft.
The cso files are created with Microsoft Visual Studio.
Use Microsoft Visual Studio to work with *.cso files.
Software apps that create cso files:
Microsoft Windows
Multiplatform
Software applications that handle other tasks involving cso files:
Microsoft Windows
Multiplatform
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