Why We’re Building Parallel Systems

WHY WE’RE BUILDING PARALLEL SYSTEMS

Much of the tremendous increase in single processor performance has been driven by the ever-increasing density of transistors—the electronic switches—on integrated circuits. As the size of transistors decreases, their speed can be increased, and the overall speed of the integrated circuit can be increased. However, as the speed of transistors increases, their power consumption also increases. Most of this power is dissipated as heat, and when an integrated circuit gets too hot, it becomes unreli-able. In the first decade of the twenty-first century, air-cooled integrated circuits are reaching the limits of their ability to dissipate heat.

Therefore, it is becoming impossible to continue to increase the speed of inte-grated circuits. However, the increase in transistor density can continue—at least for a while. Also, given the potential of computing to improve our existence, there is an almost moral imperative to continue to increase computational power. Finally, if the integrated circuit industry doesn’t continue to bring out new and better products, it will effectively cease to exist.

How then, can we exploit the continuing increase in transistor density? The answer is parallelism. Rather than building ever-faster, more complex, monolithic processors, the industry has decided to put multiple, relatively simple, complete processors on a single chip. Such integrated circuits are called multicore proces-sors, and core has become synonymous with central processing unit, or CPU. In this setting a conventional processor with one CPU is often called a single-core system.