1.1 Introduction

There is no greater mistake than to call arithmetic an exact science. There are … hidden laws of number which it requires a mind like mine to perceive. For instance, if you add a sum from the bottom up, and then again from the top down, the result is always different.

Maria Price La Touche, 1824-1906

… I submit to the public a small machine by my invention, by means of which you alone may, without any effort, perform all the operations of arithmetic, and may be relieved of the work which has often times fatigued your spirit. …

Blaise Pascal, 1623-62


The history of computers has two starting points. In one sense, it began during World War II, when a team of scientists and engineers at the University of Pennsylvania, in Philadelphia, invented a general-purpose electronic digital calculator known as ENIAC, or Electronic Numerator, Integrator, Analyzer, and Computer. Consisting of 18,000 vacuum tubes, occupying most of a large room, and adding 5,000 ten-digit decimal numbers a second, ENIAC was a revolutionary development, light years ahead of any other calculator. But it was not a computer in the strict meaning of the term. It could not store a program – a list of instructions that tells a computer what to do – and its operation was controlled by the physical rearrangement of thousands of wires and switches. Whatever a computer is – and we shall go into that later in this book – it must be able to store a program; otherwise, it isn’t all that different from a calculator. Although ENIAC wasn’t a bona fide computer, it quickly led to the invention of one, and today’s computers are its direct descendants.

In another sense, however, the history of computers commenced with the invention of the abacus, probably in Babylonia (now Iraq) five thousand years ago. This humble tool was one of the first, and certainly one of the most effective, embodiments of a momentous idea – the notion of using a machine to help us perform intellectual work. However obvious this idea may seem today, its discovery initiated a long chain of technological developments that led, by way of countless wrong turns, dead ends, and technological breakthroughs, to the invention of ENIAC and the stored-program computer. The history of computers is the story not only of a certain kind of machine, but of the progress of a great idea from sliding beads on a frame to a machine that could retain a program. Our history, then, properly begins with that most humble of mathematical instruments, the abacus.