Here you go; a quick search with regards to your x6 found this on Wikipedia...
Dynamic Performance Control
The X6 marks BMW's first use of its new Dynamic Performance Control system, which works in unison with xDrive all-wheel drive, both being standard on the X6. DPC is a drivetrain and chassis control system that works to regulate traction and especially correct over- and understeer by actively spreading out drive forces across the rear axle. Torque is distributed not only between the front and rear wheels (xDrive) but also from side to side at the rear, for improved agility and added stability (through the DPC rear axle). This lateral distribution of torque is commonly known as torque vectoring.
The DPC differential features clutch packs on both output sides that are actuated by an electric motor. The clutch pack activates a planetary gearset which causes one wheel to be overdriven. A conventional control system will use the brakes to reduce the speed of the faster moving wheel (which is the one with less traction)and reduce engine power. This leads to increased brake wear and slower than optimal progress. The DPC system speeds up the slower moving wheel (the one with the most traction) in order to maintain stability when needed. For example; while turning, the outer wheel is overdriven to provide greater acceleration using the traction advantage through the dynamic loading of the outboard wheel in cornering. In an oversteer situation, the inner wheel is overdriven to regain traction balance.