Theres a lot of word choice issues in this discussion. A generator, like on a old fashioned bike light, does not require a field winding it uses a magnet. Magnets can't be controlled as you'd guess so they're not to popular above a couple watts. Even cars don't use them, at least not for decades now.
Generators have more parts and are pretty finicky and delicate compared to alternators which are mechanically pretty simple beasts in comparison.
Alternators are electrically controllable and have a field winding.
Something like a diesel locomotive has a couple stages with a small 32 volt generator providing enough field current to run a small alternator which provides the field for the big alternator which connects to the drive motors. In the old days they used DC drive motors but for decades now they basically have multiple giant rolling VFDs and ac motors. VFDs are more reliable than mechanical commutators, which sounded crazy in the old days but its true.
Generators have more parts and are pretty finicky and delicate compared to alternators which are mechanically pretty simple beasts in comparison.
Alternators are electrically controllable and have a field winding.
Something like a diesel locomotive has a couple stages with a small 32 volt generator providing enough field current to run a small alternator which provides the field for the big alternator which connects to the drive motors. In the old days they used DC drive motors but for decades now they basically have multiple giant rolling VFDs and ac motors. VFDs are more reliable than mechanical commutators, which sounded crazy in the old days but its true.