BMW model Naming and Nomenclature
Since the late sixties BMW started assigning what is known as an 'E' code to their car models.	The 'E' designation of a model stands for 'Entwiklung' or "Evolution'. Each new 'E' code represents a new model.
Since the early seventies, BMW also started separating their cars by series.	A series designation represents the cars size and type of use. Good examples are the popular 3 series cars.
The model designation on the tail of the car tells you the series and something about the engine.	The three digit model designation common on most models tells you the model series and the the engine displacement. Thus a '325' is a three series with a 2.5 liter motor. (some exceptions apply due to as best we can tell marketing reasons)
In addition to the numbers in a cars model badge, the letters tell about body style or model specific info.	The letters such as 'i' or 'is' or 'ix' in model badges indicate additional specific info about the model. We have more info on this here.