cso is: cso is a file extension od C ISO zipped cd backup. It may be opened by DevHook.
It is a zipped Cd backup file format. Probably it is a PlayStation Portable game.
For playing PSP, you should use 2gb Sd or Memory Stick Duo Pro. However you are not able to open those files with card directly, you might need additional software.
You can download Devhook software and install to your PSP. You can easily find a document about its usage on the internet.
Cso File format viewers or openers
Cso File related links.
No links for cso file.