Weighing 30 tons and occupying an entire basement, the 1946 Eniac computer, dubbed the ‘giant brain’ by the press, was the plus-sized ancestor of today’s smartphones.

Eniac’s role in the history of computing is equally colossal, with the pioneering machine shaping the way computers were designed from that point forward.

Compared to the electromechanical machines that came before, the Eniac (Electronic Numerical Integrator and Computer) was 1,000 times faster, capable of adding 5,000 10-digit numbers a second. Designed to help the US Army calculate artillery trajectories, such was the confidence in Eniac that it was even used to verify the destructive power of early US thermonuclear bombs.

Yet, as with many of the earliest computers, the University of Pennsylvania machine had some fundamental limitations in how it operated.

While today’s computers work by installing apps, the Eniac took a different approach.

Unlike modern PCs, software wasn’t stored in the Eniac’s memory. Instead the Eniac was made up of a collection of machines that carried out a variety of different arithmetic calculations. Each of the machines that made up the Eniac could be manually wired together to perform complex operations, utilising more than 17,000 electronic valves between them.

While the Eniac could execute modern programming constructs such as loops, each time the computer was programmed it had to be laboriously rewired by teams of operators manually plugging cables into boards.

“The reason it was designed this way was because the electronic valves they used could do computation very quickly,” said Johannes Blobel, who has been working on a project to build a partial reconstruction of the Eniac at Heinz-Nixdorf MuseumsForum in Paderborn, Germany, one of the world’s largest computer museums.

“If you had to read in your program from a very slow device like a punch card reader, then that wouldn’t help at all, because that would be the bottleneck.”

But after witnessing the drawbacks of the Eniac’s constrained design, mathematician John Von Neumann, and the Eniac’s creators John Mauchly and J. Presper Eckert of the University of Pennsylvania, were struck by an idea.

What if the programs that ran on the computer could be stored in the same fast memory as the data? That concept became known as stored-program architecture and informs the design of computers to this day.

“That was basically the place where the idea of all of our modern day computer architectures came from,” said Blobel.

While Von Neumann is credited for outlining the architecture in the paper Draft Report on EDVAC, greater recognition is due both to the Eniac and its designers, whose work contributed to the ideas laid out in the seminal report, says Blobel.

“The report was never meant for publication and only stated Von Neumann’s name, and ever since this architecture has been known as Von Neumann, even though it was greatly influenced and maybe also developed by Eckert and Mauchly.”

Bringing the Eniac back to life

The work by the Heinz-Nixdorf MuseumsForum to preserve the memory of the Eniac was recognised last week, when the rebuild project won the Tony Sale Award, an annual prize run by the UK Computer Conservation Society and sponsored by Google.

Starting in 2014, the museum decided to rebuild one of the 40 panels that made up the Eniac, in this instance an accumulator that could be used to carry out addition, subtraction, multiplication and even more complex operations, such as calculating Fibonacci numbers.

Visitors to the exhibit can program the panel by turning the dial and plugging in cables, and see the output of their calculators on the neon lamp display.

The reconstructed Eniac has the look and feel of a simplified panel from the original machine, from the dials and the cables to the distinctive black ‘wrinkle’ paint that took weeks to source.

“It was a huge difficulty to find the good switches and good cable connectors. The hard task was to find someone who was able to do the special painting from that time,” said Dr Jochen Viehoff, director of the Heinz-Nixdorf MuseumsForum.

“It was my expectation that the look and feel of the machine, that when you touch the surface, this should be perfect.”

Such was their dedication to getting the aesthetics of the machine right, the pair ordered more than 10 different switches from different suppliers, as part of their quest to perfectly reproduce everything from the sound a switch made when flicked to the force needed to turn a dial.

However, while the panel’s appearance apes the original, it was necessary to simplify its operation by cutting the number of dials and cables.

“We decided to reduce the complexity of the machine down to a level that every visitor in the machine can get the look and feel of the machine, what it meant to program the machine,” said Viehoff, who added the machine can perform calculations on up to five-digit decimal numbers.

Inside the machine is distinctly more modern than the original Eniac, with the actual calculations carried out by an Arduino microcontroller, which receives its data for calculations from the panel’s dials and plugs.

Being entirely faithful to the original Eniac and using electronic valves wasn’t feasible for the museum, as it would have required a steady supply of replacement valves and having a repair crew on standby to keep the exhibit working the required six days a week.

Blobel hopes that giving visitors a chance to have a sense of what it felt like to use the Eniac, to experience the click of the dials and snap of the plugs, will help fix the importance of the pioneering computer in their mind.

“By trying out such a machine, even if you don’t remember all the details, if you hear the name Eniac, you’ll hopefully know what people are talking about.”