The original NNN system rembled NNN2 where the binding meets the boot,
but did not have the grove binding/boot interface. With the grooves,
there is now greater connection between binding and ski, which allows
for greater control and energy transfer. NNN and NN2 systems NNN-BC
(backcountry) resembles the old system, but is both wider and
presumbably heavier duty for true back country skiing. However, I
think most backcountry/telemark skiers continue to use three-pin. I
ski on skinny skis, so I'm not sure about advantages there. Each of
these systems is distinct and cannot be used with the other, and I
doubt you coud buy NNN now, it has gone the way of the Super Eight
camera.

A.