Flux-Reversal (FR) PM (FRPM) machines can be considered as stator-surface-mounted PM (SSPM) machines, where normally a pair of magnets with reversal magnetization polarities are mounted on the surface of each stator tooth. Hence, the SSPM machines and the conventional rotor surface-mounted PM (RSPM) machines are rather similar since both machines house the PMs in the air-gap, and the only difference is the location of magnets in stator side and rotor side, respectively. In this paper, a comparative study between SSPM and RSPM machines is conducted to investigate the difference including topology, operation principle, and performance. First of all, the topology of both machines is compared. Then, the operation principle in both machines is analysed based on the air-gap field modulation theory. Correspondingly, the characteristics of flux density harmonics either due to PMs or armature reaction.