Betweenthemanual and automatic transmissionis a very importantdifference is that, manual transmissionthroughthelocktodifferent diametersof the gearto the output shaftto achievethechange gearratio, and theautomatic gearboxbut withadifferentarrangementofthesameset of gearsto produce differentgear ratio.Thatset of gearsiscalledaplanetary gear. Anautomatic transmission iscomposed of a wholetwo planetary gearcombination.