A single cam operates both intake and exhaust valves through roller rocker arms. there are actually two lobes on the cam (although it is difficult to see), but since it is a single piece, so still considering it a single cam. Technically speaking it has a sideshaft, since the camshaft runs along the side of the engine. This was a common arrangement for early single cylinder engines, a multiple cylinder engine would require each cylinder to have its own sideshaft, so it’s easy to see why this mechanism disappeared.