Internal Voltage Regulator

[connerm]

Greetings,
For fun and excitement, I've been reading the threads which have to do with voltage regulators. My 95 e300d is approaching 195k and I'm always trying to stay one step ahead of the game replacing regular wear items before they fail, i.e. pads, rotors, belts, pulley, fan clutch, leaky trans cooler pipes, ignition tumbler, etc.
My limited understanding is that my 95 e300d alternator has an internal voltage regulator. How does an internal voltage regulator differ from an external one which can be replaced? I am assuming that the whole alternator gets replaced when it fails to charge. Thanks.