CSO File

What are CSO files and how to open them

Are you having problems opening a CSO file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your CSO files.

What is a CSO file?

CSO files have multiple uses, and Compressed ISO Disk Image is one of them. Read more about the other uses further down the page.

Compressed ISO Disk Image

Files containing the .cso file extension are compressed image files that are most commonly used to archive games designed for use on the Playstation PSP portable gaming system. The CSO file format was the first compression method for ISO file purposes.

The CSO files are saved in an ISO disk image format and may contain up to nine levels of compression. It is important to note that the more compression a CSO file has, the longer it will take for the disk image to load. This can significantly impact the user's gameplay or computing experience.

How to open CSO files

Important: Different programs may use files with the CSO file extension for different purposes, so unless you are sure which format your CSO file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested two different CSO openers which you will find listed below.

Last updated: September 19, 2026

All known file formats using extension .CSO

While Compressed ISO Disk Image is a popular type of CSO-file, we know of 2 different uses of the .CSO file extension. Different software may use files with the same extension for different types of data.

DirectX Compiled Shader Object

DirectX Compiled Shader Object files are binary files produced by compiling High-Level Shader Language source code designed for use with Microsoft's Direct3D. They hold shader byte code and metadata so that a Direct3D application can load the shader at run time and link it into the graphics pipeline without recompiling the source each time.

These files are generated by Microsoft's shader compilers, such as fxc.exe for older shader models or dxc.exe in newer toolchains. The process begins with writing shaders in HLSL source form, then compiling them into this compiled shader object format, which applications then supply - often via functions like CreateVertexShader or CreatePixelShader (in Direct3D 11) or by embedding binary blobs into pipeline state objects (in Direct3D 12) - so the GPU driver can execute the shader directly. This avoids runtime overhead of compiling shader code from text.

Internally, these files usually begin with the ASCII signature DXBC in their header; inside, they contain identifiable sections for input signatures ("ISGN"), output signatures ("OSGN"), resource definitions ("RDEF"), and shader statistics ("STAT") among others. These markers let tools and the runtime parse layout, resources, and performance properties embedded in the shader object.

Various apps that use files with this extension

These apps are known to open certain types of CSO files. Remember, different programs may use CSO files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about CSO file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.