4.8is steering is Servotronic
Effortless agility when parking, light-footed responsiveness and stability at higher speeds: Servotronic adjusts the amount of steering assistance to suit the current speed, enhancing driver comfort by lowering the effort needed to turn the steering wheel.

The Servotronic control unit adjusts the amount of steering assistance to suit the speed of the vehicle. An electromagnetic valve accurately controls the amount of force applied by the steering hydraulics, enabling outstandingly precise steering that suits your current driving situation. Conventional power steering systems, by contrast, regulate the power steering in relation to the engine's RPM. The electromechanical steering system EPS uses an electric motor to achieve the same effect.
Thanks to Servotronic, driving along narrow streets or parking becomes easier as it requires minimum effort to turn the steering wheel. The power assist progressively decreases when the vehicle speeds up, ensuring greater stability, improved precision and smoother vehicle behaviour.

Here's the difference on steerings for 3.0i, 4.4i & 4.8is:

3.0i and 4.4i models – according to engine speed, providing a moderate reduction of steering effort at very low speeds and in parking (engine speed below 1500 rpm) while preserving ultra-precise road feel at normal to high driving speeds.

4.8is – according to vehicle speed (Servotronic), which reduces steering effort in parking and at very low speeds more than the engine-speedsensitive assist does.

And this is what Active Steering(not on E53) is in detail:
The new dimension in steering comfort: Active Steering offers precision, agility and comfort in every driving situation.

At the heart of the new Active Steering system is the planetary gear set integrated into the steering column. An electric motor in the joint adjusts the front wheels' steering angle in proportion to the Sedan's current speed.

When driving at lower speeds - such as in city traffic, when parking or on winding mountain roads, Active Steering increases the size of the steering angle. The front wheels respond immediately to small movements of the steering wheel, enabling the driver to manoeuvre through tight spaces without needing to make multiple turns of the steering wheel. Parking is easier and agility enhanced.

At medium speeds, steering is also easier. And to ensure smoothness at higher speeds, as of around 120 to 140 km/h (depending on the model) Active Steering becomes more indirect.

Active Steering therefore reduces the amount of change in the steering angle for every movement of the steering wheel. This gives the driver the advantage of more precise steering at higher speeds, and ensures great stability and more comfort.

If the vehicle is threatened with instability, such as by oversteering or braking on a changeable surface, DSC identifies the problem and can use Active Steering to help overcome it. For example, in order to reduce unsafe yaw, Active Steering can increase the angle of steering wheels faster than even the most expert driver.

Active Steering does not interrupt the direct connection between steering wheel and front wheels, so that even in the unlikely event of a complete failure of the electronic systems, the BMW remains completely controllable at all times. This is because at the first sign of any problems, an adaptation mechanism blocks the Active Steering immediately using a pivot so that the driver is permanenty in control of the situation.