.3DS vs .CCI ROM File Formats?

I’m confused about some of the different file formats for 3DS game ROMs that Citra is able to interpret. I think Citra can open .CCI and .3DS files, but I’m not quite sure what the differences between those two file types are. Are there advantages to using either one, or does it not matter at all? Are there other file formats for 3DS ROMs that Citra is able to play? What is the recommended file format that I should be using?

In theory, there’s no difference between them.
Also, Citra is able to play .cxi , .3dsx, .axf and .elf files, being the 3dsx and the elf files 3DS homebrew, and the cxi files, dumped Installed Files from the own 3DS, like games bought from the eShop or things like Face Raiders, if I’m not wrong.

  • .cci and .3ds are two file extensions for the exact same format: NCSD. This is the format of 3DS cart images, and they’re basically a container for several NCCH files (see below).
  • .cxi and .app are the file extensions for NCCH files. These are basically 3DS "exe"s, but they also contain data for the game/application. NCCHs can also be “data-only”, and those are use in NCSDs to hold the game manual and cart-supplied system updates. Titles installed to a 3DS or SD will be stored directly as loose NCCHs.
  • .3dsx is the homebrew format that can be used with various exploits (*hax). It’s similar in purpose to a cxi, but has a simpler and more flexible format for increased compatibility.
  • .elf and .axf are ELF files, which are a raw program binary, this is the result of compiling an application, but it’s usually converted to a 3dsx (or NCCH in the case of official games) for distribution. This format is mostly useful for homebrew developers.
  • .cia is another important file format that is not supported by Citra. A CIA is a packaging format used by Nintendo. CIAs hold NCCH files, which can be installed to the 3DS NAND or SD card. This is why you can convert a CIA to a NCSD and vice-versa, they both just hold NCCHs. The difference is a NCSD is designed to allow direct access to its contents, while a CIA is meant to be unpacked to the 3DS system first.
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