This simple DIY is an in-depth alternator replacement procedure on a bmw e36. It is a relatively simple and quick job, however it is very important to know as a failed alternator will cause a non-starting car and/or the car to cutoff while driving.
This particular vehicle is a 1995 BMW 318i, the alternator was more than likely original to the car and it has more than 140,000 miles on it. 
Typically alternator replacement is needed in two cases, the first is that the regulator inside the alternator has failed and it is sending to little or too much power to the battery. The second reason, is when the bushings fail inside the alternator and cause a horrible squeaking noise, especially at higher rpms.
This alternator was replaced for the second reason, you can hear in the video the whining that the alternator makes at high rpms. 
Alternator replacement on an e36 318i should take no more than one hour.
Several common components to check while replacing the alternator is the idler pulley, tensioner assembly, and serpentine belt.