Mitsubishi S(et) Bits

Is there any difference between the S type bits and the M type bits. I know they call S type "step" relays and M type "internal relays".

The S is indicated that it is a step relay.
It depends on what CPU you are using. In the FX range the S relays are true self reseting step relays. In the A and Q series they are normal internal realys

Thanks a bunch. I wondered if they were not actually resetting. I do have an A series.