Dolby Atmos or 5.1

[MOS3]

Is dolby atmos a different mix than say... 5.1? I know it might sound stupid what I’m asking but I don’t know if it just some sounds coming from the upper speakers or a completely different mix. I don’t have a dolby atmos setup, just a 5.1, so I’m not sure what happens if I choose atmos as the audio option on a movie as opposed to regular 5.1. Will I not get the audio that was supposed to come from the upper speakers at all or will it come from the available ones. Should I choose Atmos because it’s a better quality audio mix or 5.1 because it matches my setup. I hope I’m making sense here