This article is good but goes overboard in explanation. AWD and 4wd by all accounts are just buzz words for having front and rear differentials. In actual use, a 4x4 (a term I mean to refer to both 4x4s and awds as its just a buzz word) has three differentials. A center diff splits power from the transmission out to the other diffs, which split power to the wheels. There are three general types of diffs, whether centered or front or back:
Open (just gears, sends power the the least resistant path)
Locked (a spindle connects the input directly to the output and all three spin proportionally)
Posi (multiple ways of actuating this, can be viscous clutch, electric or air powered actuation, or mecanical geared torsion style - regardless the point is to keep power at all wheels, some with variable speeds allowing for turns - others act like a spindle)
Most "awd" cars have a open gear in all three diffs. My jeep has a spindle in the front and center and an air locker in the rear (not the stock design). My old BMW 325ix has a viscous clutch in the center and in the back, and open in the front. My dad's audi has open gears all around and uses the brakes to actuate were the power is delivered. At the end of the day tho, its three differentials.
There is a non-buzzword practical difference; one system cannot be driven on dry pavement (part-time 4x4). One system can be driven on dry pavement (full-time AWD).
Open (just gears, sends power the the least resistant path)
Locked (a spindle connects the input directly to the output and all three spin proportionally)
Posi (multiple ways of actuating this, can be viscous clutch, electric or air powered actuation, or mecanical geared torsion style - regardless the point is to keep power at all wheels, some with variable speeds allowing for turns - others act like a spindle)
Most "awd" cars have a open gear in all three diffs. My jeep has a spindle in the front and center and an air locker in the rear (not the stock design). My old BMW 325ix has a viscous clutch in the center and in the back, and open in the front. My dad's audi has open gears all around and uses the brakes to actuate were the power is delivered. At the end of the day tho, its three differentials.