What Is a CSO File?

Yours is most likely a compressed ISO image

What to Know

  • It's most likely a compressed ISO image, but another format shares the file extension.
  • Open one with Format Factory or PSP ISO Compressor.
  • Convert to ISO, DAX, or JSO with Format Factory.

This article explains the different formats that use the CSO file extension, how to open each kind, and how to convert one to a different format so that it's usable in other software.

What Is a CSO File?

A file with the CSO file extension is most likely a compressed ISO image file. The format is also referred to as "CISO." It was the first compression method available for ISO files and is often the preferred method for archiving PlayStation Portable games. The format supports up to nine compression levels.

Although it's less likely, some CSO files may instead be compiled shader object written in the Microsoft-developed High-Level Shader Language (HLSL).

CSO is also short for technology terms that don't have anything to do with these formats, like computer security officer, C shared object, cluster supporting object, client support operations, and custom scenery object.

How to Open a CSO File

You can open a compressed image CSO file with Format Factory, PSP ISO Compressor, or UMDGen.

Those two latter programs are downloaded as RAR archives. You can use 7-Zip (it's free) to open them.

Original PlayStation Portable game console

Evan-Amos/Wikimedia Commons

Visual Studio opens compiled shader objects.

How to Convert a CSO File

PSP ISO Compressor can convert CSO to ISO and vice versa. It also supports saving CSO to DAX and JSO, which are similar compressed image formats.

A similar program, ISO Compressor, is another way to decompress CSO to ISO.

UMDGen can convert CSO to ISO and DAX.

Still Can't Open It?

A file that won't open at this point, after trying the above suggestions, is most likely not in either of the formats mentioned here. This can happen if you've misread the file extension, something that's really easy to do when it's just three common letters.

For example, maybe you really have an SCO file. While it might look similar to CSO at first glance, it's most likely a backup image that only works with TotalRecovery.

CSD is another example. There are several formats a CSD file could be in, so it might need Steam if it's a game data backup, or Manga Studio if it's a 3D scene.

Whatever the file extension is, reread it and then start your search again to find the format it's in and ultimately which program is responsible for opening or converting it.

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