a quote from Steve Jobs, explaining that the breakthrough invention was the fractional horsepower motor:

"Let’s look at the brief history of computers. Best way to understand it’s probably an analogy. Take the electric motor. The electric motor was first invented in the late 1800s. And when it was first invented, it was only possible to build a very, very large one, which meant that it could only be cost-justified for very large applications. And therefore electric motors did not proliferate very fast at all.

But the next breakthrough was when somebody took one of these large electric motors and they ran a shaft through the middle of a factory and, through a series of belts and pulleys, brought…shared the horsepower of this one large electric motor on 15 or 20 medium-size workstations, thereby allowing one electric motor to be cost-justified on some medium-scale tasks. And electric motors proliferated even further then.

But the real breakthrough was the invention of the fractional-horsepower electric motor. We could then bring the horsepower directly to where it was needed and cost-justified it on a totally individual application. And I think there’s about 55 or so fractional-horsepower motors now in every household."