The Personal Computers Explained (according to Jobs):
The electric motor was invented in the 1800s, but it was not cost effective to build in a factory. Then someone took the electric motor and connected it to 15 smaller machines in a factory, thereby allowing a large motor to be cost justified in a medium level task. Then there was the invention of the fractional electric motor which has a 1/55 horsepower motor. Today that is in everyhousehold in 1983.
The Eniac was the first computer in 1947 (http://en.wikipedia.org/wiki/ENIAC) to track ballistic missiles. Then in the 1960s there was this idea of time-sharing of a super computer between people through a terminal so that 5 people could use the one computer at one time because the computer was so fast they all thought it was only working for themselves. This justifies super computers in universities. Fractional horse power computing was the innovation of Steve Jobs and Wozniak. The only reason Apple was successful is that they innovated 5 years before anyone else had by creating fractional horse power computing. They had closed off the terminal concept of computing where you would have to go to a university terminal that was connected to a large computer (called time sharing because each person would have 30 minutes with this powerful machine).
A computer is just doing a series of simple instructions but doing so very quickly. So then we build a higher levels of abstraction are translated down to simple instructions.