Historically, different answers to this question – that is, different visions of computing – have helped inspire and determine the computing systems humanity has ultimately built. Consider the early electronic computers. ENIAC, the world’s first general-purpose electronic computer, was commissioned to compute artillery firing tables for the United States Army. Other early computers were also used to solve numerical problems, such as simulating nuclear explosions, predicting the weather, and planning the motion of rockets. The machines operated in a batch mode, using crude input and output devices, and without any real-time interaction. It was a vision of computers as number-crunching machines, used to speed up calculations that would formerly have taken weeks, months, or more for a team of humans.