Full time 4WD
Goal: Better on-road handling stability.
In addition to engine, transmission and transfer case a full time 4WD will need a "center differential". Center differential because it sits in the center between the front and rear drive shafts.
The fact that part time 4WD can not be used on dry pavement made this development necessary if one wanted to benefit from the stability enhancing capability of 4WD for modern cars.
This 4WD system can stay in 4WD full time. That's why its called "full time 4WD". Sometimes also referred to as "permanent 4WD".
Full time 4WD layout:
A = center differential
B = front axle differential
C = rear axle differential