@macu Think of a "core" as an emulator, for instance there are many emulators for SNES: Snes9x, higan, etc... Each one is a core.
Then there are libretro adapted cores (the ones that use the retroarch environment) and standalone cores (with their own environment, configs, etc). Recalbox uses libretro and standalone cores, sometimes you can choose between them as is the N64 case. Sometimes not (Dosbox for instance). The devs choose cores availability depending on the system (Raspi, PC, etc), they do so with performance un mind. N64 emulation is tricky, especially in lower end machines like Raspberry Pi, so its a matter of trial and error which core is better for a game.
