A disc chipper is a lot like the old heavy engines of the past, heavy fly wheels/engines that turn slower than modern engines. Once the fly wheel/chipper disc gets up to speed, it doesn't take much power to keep it going, so you have more power for chipping. Drums don't have near as much diameter so less momentum (diameter seems to be more important than just weight alone). To me, a disc chipper shears the wood, a drum chipper because of a radial arc cutting path - whittles away a log. I have looked at my drum throwing chips and it seems the chips really come out the discharge shoot at a radial also. The disc chipper it throws chips as strait and fast as an arrow. I have to say, a disc chipper is pretty finicky with needing to keep the blades sharp for top performance, a drum chipper will let you get by a little longer with not so sharp blades.