In this survey, the size effect on magnetization configurations and magnetization reversal of a Permalloy
magnetic nanodot were studied by using micromagnetic simulation. The coherent rotation is a dominant transition
process for the dots with smaller radius. It has been shown that as the radius of dot becomes larger, the transition mode
tends to be appeared in "S" state and finally leading to single and double vortex states. Thicker dots are found to
reverse their magnetization by nucleation and propagation of their vortex states, when the field is applied parallel to the
dot surface.