The "old style" (roller bearing?) bearing has a "floating" (or independent) race that is pressed onto the crank. The "new style" (ball bearing) has a fixed race in the bearing. You need to remove the race from the crank nose if you want to go from the old style to the new style.
Also, I believe that the general consensus (from the old days) was that the "old style" roller bearing was preferred as it allows lateral float, whereas the ball bearing doesn't. However, I think that was preference based on historical precedence, and I'm not sure if there is any basis in fact that one bearing is better than the other. Although if there is evidence one way or the other, I would like to read it.
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Phil
(New bike pending...)
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