International 4800 - 4x4 system explained

Just acquired an older 4800 4x4. Curious about the 4x4 systems in International 4800s. Front driveshaft spins while driving and there’s a front axle IN/OUT button. Without me having to jack the truck up and test myself, what does the Front Axle IN/OUT button do? Assuming it either locks the hubs, or locks a center diff in transfer…or would be great if it locked the front axle altogether but that seems too good to be true.
Thanks

 

This is also assuming everything is working and the front driveshaft is supposed to be spinning…unless it’s stuck in 4WD. I have seen AWD emblems on some of these Internationals so I’m assuming the front driveshaft is always spinning with the rear.

 

Copy so the Front Axle IN/OUT button is basically a center differential lock/unlock. Front Axle IN = power to front axle. Front Axle OUT = no power even tho driveshaft spins since there aren’t manual locking hubs correct ?

 

Also just to confirm these aren’t AWD systems?