Note: In place of the word 'firmware', 'BIOS' is sometimes used, since BIOS is more descriptive, and people know what it means. To be OK we need to be able to build and run that binary on an FSDG compliant distribution without any nonfree software.

Compilation and binaries: If we have a binary like VLC for Windows, and that VLC is free software, the binary could be nonfree (like when VLC is released through the appstore) or it could contain nonfree system libraries (like microsoft or compiler related libraries) or require nonfree dependencies to build (probably like the VLC for iOS that is not released through the appstore).

BIOS: when the emulator requires a non-free firmware file to run in the first place, meaning that unless a free firmware was created, free development or use of the emulator would not be possible.Images: when only non-free images games appear to be available, meaning that the emulator could be used in a completely free manner if free images did exist or were created, example: Playstation or Sega Saturn images or images burn from a CD o DVD to use on an emulator.ROMs: when only non-free ROMs appear to be available, meaning that the emulator could be used in a completely free manner if free ROMs did exist or were created.There are actually two potential problems with the fully free (libre) emulators in Arch Linux in that respect: Parabola GNU/Linux is currently blacklisting many emulators provided by Arch Linux due to a decision made in the thread Emulators which concludes that most emulators do not belong in a 'free as in speech' operating system because their exclusive purpose is to run games like ROMs and images, which are assumed to not have a free license.

5 List of Emulators which run only on Wine.

Sega emulator linux