1. if a modern-day MacBook Air operated at the energy efficiency of computers from 1991, its fully charged battery would last all of 2.5 seconds. Similarly, the world’s fastest supercomputer, Japan’s 10.5-petaflop Fujitsu K, currently draws an impressive 12.7 megawatts. That is enough to power a middle-sized town. But in theory, a machine equaling the K’s calculating prowess would, inside of two decades, consume only as much electricity as a toaster oven