When people are 50 years old, they often think about slowing down, putting their feet up, and investigating hobbies that can be done indoors but require no heavy lifting.

Racking up half a century of existence demands at least a moment or two of reflection.

And if that goes for humans, it also goes for computers, or at least the commercial species, which reaches the 50-year milestone this week.

Much of the pioneering work that went towards making that all important first sale, was done towards one end - winning World War II.

War work

In Britain a team led by Alan Turing at the Bletchley Park code-breaking centre was making the Colossus, a machine that could crack encrypted messages far faster than any human could.

In the US John von Neumann and reserachers from the Moore School of Engineering at the University of Pennsylvania were building Eniac (Electronic Numerical Integrator and Computer) that was designed to work out firing tables for artillery batteries.

I think there's a world market for maybe five computers

Thomas Watson, IBM chairman, 1943

In Germany Konrad Zuse was developing the 'Z' series of computers in work funded by the Air Ministry.

His prototypes are now seen as the first modern computers because they could be reprogrammed to do different tasks. Earlier machines could carry out only one function or they had to be rewired every time they had to carry out a new task.

The Philadelphia story

In 1946 the two pioneering engineers who did most of the work on Eniac, J. Presper Eckert and John W. Mauchly, decided to commercialise the work they had done, and set about creating a company that could build and sell these fabulous machines.

The result of the work in their Philadelphia office was the Univac (UNIVersal Automatic Computer). But, like so many engineering projects before and since, its development was dogged by cost-overruns and delays.

The Manchester Mark I - forerunner of the Ferranti

So much so that Eckert and Mauchly were forced to sell their company to Remington Rand if they were to have a chance of making the Univac work.

The new owners provided the cash to finish development of Univac and the first one was sold to the United States Census Bureau and a formal dedication ceremony was held on 14 June, 1951 - hence the 50-year anniversary. In fact the machine had been working since late March.

Commercial success

Eckert and Mauchly were challenged to the title of selling the first commercial computer by the British team that developed the machines used to crack encrypted messages during the war.

Some of this group of scientists had gone on to work at the University of Manchester and it was here that they worked with Ferranti to develop the Mark I computer. The University was the first customer for this improved machine and others followed soon after.

Compared even to every day machines of the post-war period, the Ferranti Mark I and the Univac were huge. The computational heart of the Ferranti was held in two bays, each of which was almost five metres long, over two metres wide and over one metre wide.

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The Univac was even bigger. The central section of it was about as big as a one-car garage. It had a hollow core and doors that let people walk inside, and was reputedly so big that some engineers tasked with looking after the beast put their desk inside so they could enjoy the luxury of an air-conditioned office.

That cooling was needed because inside the eight-ton behemoth were 5,200 vacuum tubes driven by a 125 kilowatt power supply. All this for the equivalent of a memory of a mere 1,000 words.

Despite the size and power requirements and cost, about $1 million, the Univac was popular for its day. In the event 46 were produced and installed.

As well as being the first commercial computer, the Univac also started the computer industry on the relentless upgrade treadmill that still characterises it today.

The Univac itself was superseded in 1956 by IBM which released the 704 and 705 model computers that were significantly more powerful.

Today we are lucky if the machines we buy are state-of-the-art for five months let alone five years like Univac managed.