4WD mechanically interlocks the front and rear wheels (setting aside the front and rear differentials). You cannot use 4WD on clean pavement because of this; the front and rear may need to turn at different rates which 4WD doesn’t allow. It’s ok off road because the wheels can slip a little in the dirt.
AWD generally does not mechanically 1:1 interlock anything, instead using things like torque converters. This allows it to be used on clean pavement. It isn’t as robust as 4WD, and has to respond to wheel slip instead of simply being 1:1 all the time.
AWD generally does not mechanically 1:1 interlock anything, instead using things like torque converters. This allows it to be used on clean pavement. It isn’t as robust as 4WD, and has to respond to wheel slip instead of simply being 1:1 all the time.