Anaconda-

It looks like this has been clarified for you, but just to be sure I'll offer this:

The word "single" with regard to cylinder count and single (sohc) and camshafts are actually unrelated. I'm not sure but this may have something to do with your initial question.

All four stroke cycle engines have at least one camshaft somewhere (forget sleeve valve engines for this discussion). It may be in the block where it can operate valves that are also in the block (a.k.a. side valve or flathead) or if the valves are in the head, pushrods and rocker arms would be required to actuate the valves. When the cam is in the block in virtually all cases only one cam is needed even with a Vee type engine. Yes there are exceptions but they are unrelated to valve control.

The only other location for a cam is in the head, as in SOHC and DOHC. The single and double having to do only with the number of camshafts, not the cylinder count. So everything from a single cylinder to a v-12 can be of a SOHC design or a DOHC. The reason cams were moved to the cylnder heads is for more accurate valve control. So any engine regardless of the number of cylinders can benefit from an overhead camshaft design. Some of the considerations in the choice of a single overhead cam and a double overhead cam are cost, and mechanical complexity. Two cams cost more, but the valve actuation can be simpler. A SOHC design will usually require rocker arms for at least half of the valves. With the classic DOHC design the cam lobes act directly (through the shim bucket) on the valves, no rocker arm required.

Interestingly, going back to the flathead (valve in block) engines, they enjoy valve control that is every bit as accurate (maybe even a little more so since they can dispense with a cam chain) as an overhead cam engine since they also can act directly on the valve.