Roots and twin screw models have “positive displacement”, meaning that they move the same amount of air for each engine revolution, regardless of RPM. This also means that they can make boost immediately (even at low RPMs), and have a fairly linear power curve.

Centrifugal models have an exponential power curve, and must build up pressure to make boost. They make little usable boost at low RPMs, and are tuned to make full boost at redline.