well, the main difference is the TONEWHEEL GENERATOR. Ever since Hammond stopped making B3's etc., everyone (including Hammond) has been trying to re-create the sound. If you have ever played a B3000, you know that it is a hard task. Now, Im not too familiar with the Roland organs, but I know its probably a Roland vk-77. now Im sure they just try to use a virtual tonewheel system, and you can probably tell that its virtual, or electronic. The tonewheel system is just what it says. Its a wheel inside of B3, C3, A100, RT3's that gives off Tones. In Roland, Korg, and all that, there are probably Sound cards with tones in them, so its a re-created sound, and not the original Hammond Tonewheel sound. the BEST "un-Hammond" organ is probably the DIVERSI organ by Voce. Check that out, and take that Roland back.