Excellent explanation, but I think it's missing a simple point yummybear may not know: "transistors" are the unit with which we build logic on processors. More transistors means more logic on the chip. More logic on the chip means you can do more. For a long time "do more" meant "execute a single stream of instructions faster", but that hit a wall because of the reasons vidarh explained. Now "do more" tends to mean "execute multiple streams of instructions".