The Roots blower or supercharger is best known for possessing a unique capability for instantly generating different discharge pressure over a wide speed range and equally famous for generating heart rattling gas pulsation and noise at the same time.Though Roots is the oldest and seemingly simplest super-charger by construction, some fundamental questions still remain unanswered even today, such as: What is the physical nature of Roots pulsation and the conditions that trigger its happening? Where and when is it generated? How do we estimate its magnitude and travel direction? And is there a different way to tackle Roots pulsation from insight gained from the above questions?This paper attempts to answer these questions by applying the classic shock tube theory to the transient process of Roots compression. The results reveal that the nature of Roots pulsation is characterized by an abrupt flow reversal (IFF) coupled simultaneously with a pair of non-linear compression wave (CW) and expansion wave (EW) at the source. Moreover, pulsation is directly resulted from the pressure rise it generates. Pulsation Rules are deduced to predict the location of initiation, maximum magnitude, travelling directions and speed from the design parameter and operating condition of the super-charger. Based on this insight, a pro-active control strategy called pulsation trap is devised, targeting the unique characteristics of CW-IFF-EW and tackling them right at the predicted source. Preliminary test data indicate 20 dB pulsation reductions under different load and speed conditions.