The reason that we’re not increasing clock speed is not that the transistors have stopped getting smaller and faster. Even though transistors are continuing to get smaller and faster and consume less energy per transistor, the problem is running a billion transistors generates an awful lot of heat, and we can’t keep all these processors cool. Power has emerged as a primary driving factor, possibly the most important factor in modern processor design at all scales, from a mobile phone that you keep in your pocket all the way to the very largest supercomputers. The consequence is we can’t keep building processors in the way we always have by making a single processor faster and faster. When we do that, we end up with processors that we simply can’t keep cool. Instead, processor designers have turned to building smaller, more efficient processors in terms of power, and they then spend their extra resources to build a larger number of efficient processors rather than faster less-efficient processors.