ENIAC, EDSAC and Colossus... and the Difference Engine

There are lots of claims to be the first computer, depending on your definition of "computer". Babbage's difference engine was clearly a computer of sorts, although not electronic. His analytical engine was even programmable. But it was finally completed in London in 2002, 153 years after it was designed.

ENIAC, which stood for Electronic Numerical Integrator And Computer, was clearly a computer. It was started in 1943 in secret for calculating ballistic trajectories as part of the war effort. When it was finally decommissioned, it contained nearly 18,000 vacuum tubes. It was programmable, but only by rewiring its patch panel.

At Bletchley Park outside London, a major electronic computer called Colossus was developed, primarily for code-breaking during the second world war. But due to secrecy, it was decades before anyone found out about it.

EDSAC

After the war, the Electronic Delay Storage Automatic Calculator (EDSAC), was built in Cambridge by a team led by Maurice Wilkes. It was the first stored-program digital computer. Running a different program did not require re-wiring the computer, merely loading a new program into memory. Everything was done using five-hole paper tape for input, and a teleprinter for output.

The memory technology was quite primitive. It consisted of tubes filled with mercury. At one end there was a transducer and at the other end, a microphone. Bits were transmitted through the mercury as sound waves, picked up by the microphone, and recirculated. One line could hold perhaps a thousand bits. When I was an undergraduate in 1965, EDSAC was long since decommissioned, but the proudest possession of many of the lecturers was to have one of the original delay lines in their office. Although modern dynamic random-access memory (DRAM) requires regular refreshing, it can be accessed randomly. EDSAC's delay line memory was more like a disk drive; you had to wait for the bit you wanted to come around. It was not until 1955 that the MIT Whirlwind became the first computer with magnetic core memory, and thus the first true random access memory was born.

Even debugging had to be discovered. As Wilkes once said:

The EDSAC was on the top floor of the building and the tape-punching and editing equipment one floor below. [...] It was on one of my journeys between the EDSAC room and the punching equipment that, hesitating at the angles of stairs, the realization came over me with full force that a good part of the remainder of my life was going to be spent in finding errors in my own programs.

By the time I was an undergraduate computer science major at Cambridge, Wilkes was the head of the department. But he was very active, and my courses on networking and on numerical analysis were given by him. He also had a good eye for the future, playing with microprocessors during the era when they couldn't do much (compared to a time-shared mainframe). I remember in one seminar, somebody challenged Wilkes that due to speed-of-light considerations, computers couldn't get much faster. (This was in an era when the CPU would be one huge box, and when the university added the second---count 'em, both---megabyte of memory to the IBM 370 that served the whole university, it was another large box on the other side of the room. Wilkes thought for a moment, then said, "I think it means that computers are going to get a lot smaller." And they have.

After the war

After the second world war, the US and the UK took very different attitudes to the electronic computing technology that had been developed in secret during the war. As Wikipedia puts it:

A few months after ENIAC's unveiling in the summer of 1946, as part of "an extraordinary effort to jump-start research in the field", the Pentagon invited "the top people in electronics and mathematics from the United States and Great Britain" to a series of forty-eight lectures given in Philadelphia, Pennsylvania; all together they were called The Theory and Techniques for Design of Digital Computers—more often named the Moore School Lectures. Half of these lectures were given by the inventors of ENIAC.

Meanwhile, in Britain, all of the computers created at Bletchley Park were broken to bits, the plans were destroyed, and everyone was sworn to secrecy for thirty years. It was only in the 1970s that the story of Bletchley park, the people who worked there (which included my Great Aunt---although she wasn't allowed to tell me) and the invention of Colossus, the first electronic digital computer, became public. Several of the heads of computer science departments turned out to have worked there, so the knowledge was not totally lost. Recently, however, a rebuilt of Colossus has taken place and you can now go and see it. The museum is about 100 yards from Bletchley Station, which is a short train journey from London Euston.

But for sure, after the Moore School Lectures, the different attitudes about proliferating computing technology after the war meant that Britain never again had a leadership position in computers, and everything has been driven from the USA.

Building Babbage's Difference Engine

In the late 1990s, to commemorate the 200th anniversary of Babbage's birth, the London Science Museum (next to South Kensington tube station, if you want to visit) began construction on a working version using modern manufacturing techniques but working from Babbage's original drawings. It was completed in 2002 and is on view in the computing gallery. Nathan Myhrvold (of Microsoft fame) commissioned a second one, which for many months was on display in the lobby of the Computer History Museum in Mountain View, but is now in the lobby of Nathan's Intellectual Ventures, which is either a patent troll or a major resource for inventors, depending on your point of view.

BTW: If you watched last week's What's for Breakfast? video where an announcement was promised for today, it got postponed. So today's post takes its place.