Originally Posted by cuiter23
Steering boost and Active Steering are all components of the Hydraulic system implemented on modern vehicles including the e90.
No, actually. Active Steering (AS) is an independent, purely electric system. AS is a combination of electric motor and planetary differential spliced into the steering shaft. By itself, AS doesn't in any way involve anything hydraulic.
AS is an optional component in E90 cars. My car, for example, has no AS, just a traditional hydraulic boost applied to the steering rack.
Cars with AS use it for ratio changing, while boost is still provided by traditional hydraulic system. These two systems are applied to two completely different physical points: AS works in the steering shaft, while hydraulic boost is applied to the steering rack.