When dealing with BMW vehicles, it is often more convenient and apt to describe them by their chassis designation. Chassis designation is done via an E number. this guide covers 2 chassis versions of the 3 series, the E30 and the E36. There is 1 chassis covered in the 5 series, the E34. Check the charts to identify the chassis designation of your vehicle.
The reason it is more convenient to use the chassis designation in certain instances is that there is overlap of the 3 series vehicles in the early 1990's. For example, in a given year, there were two 325i's. They used different chassis' (E30 and E36) and different engines (M20 and M50), but the same name designations. To keep from confusing the 2 vehicles, use of the chassis designation pinpoints the car in question.