CSO File: What It Is and How to Open It

Your CSO 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 might not know right away what it is or how to open it. The answers depend on which type of CSO file it is.

Types of CSO Files

A file with the CSO file extension is most likely a compressed ISO Image file. The format is also 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 written in High-Level Shader Language (HLSL), which was developed by Microsoft. 

How to Open a CSO File

You can open a compressed image CSO file with:

Note: Both PSP ISO Compressor and UMDGen are downloaded as RAR archive files. You can use a file expansion program such as 7-Zip (free) to open your downloaded file.

Microsoft Visual Studio opens Compiled Shader Object files.

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.