Learn the Definition of a CSO File and How to Open It

Your CFO file is most likely a compressed ISO image file

Playstation Portable
Evan-Amos/Wikimedia Commons

If you run across a file with a CSO extension, you probably won't know right away what it is or how to open it. The answer depends on which type of CSO file it is.

Types of CSO Files

A file with the CSO file extension is most likely a CISO compressed ISO Image file. The format is sometimes just referred to as "CISO." CSO was the first compression method available for ISO images and is often the preferred method for archiving PlayStation Portable games. The CSO format supports up to nine compression levels. The highest level provides the best compression but offers the slowest load times.

Although it is less likely, some CSO files may instead be Compiled Shader Object files. These files are compiled files that were written in High-Level Shader Language (HLSL), which was developed by Microsoft. 

How to Open a CSO File

Compressed image CSO files can be opened with:

Note: Both PSP ISO Compressor and UMDGen download in a RAR archive file. The free 7-Zip program can be used to open it.

How to Convert a CSO File

Format Factory can convert CSO to ISO and vice versa. It also supports converting CSO to DAX and JSO, which are two other compressed image formats similar to ISO.

UMDGen can convert CSO to ISO and DAX.