The differential is found on all modern cars and trucks, and also in many all-wheel-drive (full-time four-wheel-drive) vehicles. These all-wheel-drive vehicles need a differential between each set of drive wheels, and they need one between the front and the back wheels as well, because the front wheels travel a different distance through a turn than the rear wheels.
Part-time four-wheel-drive systems don't have a differential between the front and rear wheels; instead, they are locked together so that the front and rear wheels have to turn at the same average speed. This is why these vehicles are hard to turn on concrete when the four-wheel-drive system is engaged.
The Advantages & Disadvantages of All Wheel Drive
All Wheel Drive (or AWD) is a system in which all four wheels of a car operate simultaneously to improve traction and handling. While it is possible for a car to have continuous AWD capabilities, it is far more common for one pair of wheels to engage only when sensors detect that the other pair has begun to slip. There are both advantages and disadvantages to AWD systems