ok---a single overhead cam means there is one cam mounted above the head driving the valves----if the car has two heads yes there are two cams----(like your car)--- dual overhead cam means there are two cams mounted above each head driving the valves--there are twice as many valves as a single overhead cam-----a car with an inline configuration can be either of theses as well but would only have one or two cams because there is only one head.....

on our cars 4.6l sohc---you have two cams one above each head---driving 16 valves-----
on the cobra motor you have a dohc-----you have four cams--two above each head--they have twice as many valves 32v-----thats why the cobra heads flow so much better--they have virtuallt twice the air flow capability of the sohc.....