If your car has hydraulic power steering you will see the reservoir for the hydraulic fluid. On my 2009 325i, the reservoir has a green cap, and its on the left hand side of engine. (some later models have a black cap)
The word 'servotronic' is confusing, because it was used for an advanced hydraulic power steering system since about 10 years ago or more. Quite recently BMW use the word to describe electric power steering systems on the latest models.