The first general-purpose electronic computer

The story

When “computer” meant a person

Until the middle of the 20th century the word “computer” did not mean a machine, but a person: someone who did calculations. In offices of science and war there were rooms full of human “computers”, often women, who with pencils, paper and simple calculating machines produced tables of numbers for guns, for stars, for aeroplane designs. During the Second World War the calculations multiplied: to hit a target accurately, American artillery needed tables showing how to tilt the gun depending on distance, wind and height. Each table took days of work, and hundreds were needed.

At the University of Pennsylvania, in Philadelphia, a physicist, John Mauchly, and a young electronic engineer, John Presper Eckert, had an idea: to build an electronic machine that would do those calculations in a few seconds. The American army, convinced, paid for the project, and in 1943 they began work, with a team of engineers and technicians.

A giant of electronic tubes

The machine was called ENIAC, from the initials of “Electronic Numerical Integrator and Computer”. It was finished at the end of 1945, and shown to the public on 14 February 1946. It was a monster: it filled a large hall of over a hundred square metres, weighed about 27–30 tonnes and used 150 kilowatts of electricity, more than a hundred homes. Inside it were almost eighteen thousand thermionic valves, glass tubes that worked as switches, together with thousands of other components and kilometres of wires. The valves got very hot, and every now and then one burned out: the technicians had to find it and replace it.

But it was very fast: it did about five thousand additions a second, a thousand times faster than the machines of the time. A trajectory calculation that took days by hand could be done by ENIAC in under a minute. At the presentation, the newspapers called it an “electronic brain”. The first real job it did, at the end of 1945, was a secret calculation for a nuclear weapons project.

The women programmers

ENIAC had no stored program: to make it do a job, its modules had to be connected to each other with cables, like in an old telephone exchange, and hundreds of switches had to be set. Every new problem took days of work. This work was done by six young women mathematicians, chosen from the human “computers” already working at the university: Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas and Ruth Lichterman. They had to learn by themselves, from the machine's diagrams, how it worked and how to give it instructions: they were the first programmers in history. At the presentation, however, their names were never mentioned, and only many years later was their role recognised.

It was not the only one

ENIAC was the first big “general” electronic computer, that is, able to solve many kinds of problem, but it was not the only one. In England, at Bletchley Park, during the war, technicians had built Colossus to decipher German secret messages, also electronic, but specialised. In Germany Konrad Zuse had built machines with electromechanical relays, and at Harvard the American Howard Aiken built the Mark I, big and slow. The English mathematician Alan Turing had imagined as early as 1936 a “universal machine”, able to carry out any calculation, an idea that is the basis of modern computers.

A decisive step was taken by John von Neumann, who in 1945 described a machine in which the program too, not just the data, was kept in memory: all you had to do was change the program, without rewiring the cables. The first computer of this kind ran in Manchester, in June 1948.