It's whatever you call this: In normal mode it's full-time 2WD (front-wheels) with power transferred to rear-wheels when front-wheel slip is detected. I don't know the specifics of other modes but would assume they have 50/50 power distribution that is infinitely-variable depending on which wheel(s) are slipping. The different modes change the amount of wheel spin allowed (a lot for sand/mud, little for snow), power transfers, body roll, throttle sensitivity and maybe a few other things.