What's the difference between single and dual overhead cam engines?

Ever wondered what people are talking about when they say "dual overhead cam"? Don't worry, because we're here to explain it ...
Chicago Tribune

To GM, the future of engines is in overhead valves

General Motors sees a future for engines with overhead valves, a technology most automakers have abandoned in favor of overhead camshafts. GM will introduce a new family of overhead-valve (OHV) V-6s ...
Los Angeles Times

Valves vs. cams? For GM, it’s no contest

General Motors Corp. sees a future for engines with overhead valves, a technology most automakers have abandoned in favor of overhead camshafts. GM will introduce a family of overhead-valve V-6 ...