Recreating a computer from history

14 July 2015

Interview with

Dr Nigel Bennee, Physicist

How much of your day is spent on a computer, looking at your phone or doingDr Nigel Bennee and EDSAC something online. It's easy to forget that just 60 years ago none of this was possible, and by today's standards the simplest calculations took weeks of combined work from people. That is, until something called EDSAC came along. EDSAC stands for Electronic Delay Storage Automatic Calculator, and was built at Cambridge University shortly after the second world war to start crunching through these complex maths problems in a much less time and 1000 times more quickly. It was the first computer built for other people to solve problems on. Today, virtually nothing of EDSAC survives, but now a team are attempting to build a working replica, to eventually put on display in the National Museum of Computing at Bletchley park. Nigel Bennée is a retired physicist building a section in his garage in Cambridge! Graihagh Jackson went to meet man and machine to for a cup of tea and a trip through history.

Nigel - Immediately after the war, Maurice Wilkes, he'd worked on radar. In radar, they had managed to get a storage device where you could store the equivalent of 72 bytes in a 5 foot tube full of mercury.

Graihagh - I mean, that's not even a Word document, is it?

Nigel - It's barely a character. You might get a tiny little icon. So, the biggest constraint to making a computer was, where can we store it? EDSAC had the largest memory that existed. They had about half a ton of mercury.

Graihagh - Which equates to how many bytes?

Nigel - 2,300 bytes.

Graihagh - It still doesn't sound that much.

Nigel - And that was the entire machine to hold all the programme, and all the data that you were going to execute.

Graihagh - It wasn't just important in terms of memory. My understanding is that lots of scientists are running lots of mathematical equations and women were taking months to do them. So, it played a pretty fundamental role in science as well, once it was built.

Nigel - Absolutely. EDSAC claimed 3 Nobel Prizes and the ladies you refer to were known collectively as computers because they computed. They had turn a handle calculator where you put the numbers on the thing, turn the handle, very elegant, but very, very slow. To put it in context, EDSAC runs at about 1500 times faster than one of those ladies would do.

Graihagh - Can we go and see it because I know you've got your own workshop dedicated to replicating it?

Nigel - Yes, let's go and see it. What you can see here is about 25 per cent of the EDSAC replica. There's three 7-foot high steel racks painted in nasty yellow colour. That's because they're in a film. The Imitation Game. These 3 racks represent the actual calculator part of the computer. A lot of the rest of the machine is to do with memory.

Graihagh - What I would describe what I'm looking at is, what looks like a series of almost bookshelves. And on each shelf, there is hundreds of metal tubes, some painted bright red, almost like a lipstick and this is just all various instrumentation to do maths like the modern day calculator, what it might have on my phone.

Nigel - Absolutely.

Graihagh - Take me through what would've happened back in the 1950s. I'm a scientist. I'd like to do - not my 2 times table, but I'd like to do something a bit more sophisticated than that. How would it work if it was in its full glory here?

Nigel - So you were - I forgot the two guys' names. They both won Nobel Prizes, but they were trying to work out how nerve pulses propagated through nerves. Their theory involved a complicated balance or imbalance of chemicals going on and these can be represented by differential equations.

Graihagh - Okay, so I've got my equation now and you didn't have a lovely keyboard. How would you translate that into EDSAC?

Nigel - You would type a paper tape.

Graihagh - Sorry, paper tape?

Nigel - Let me show you some paper tape. This is the box here. It contains paper tape. That is programme 17 and the date is 1968.

Graihagh - It's almost like braille but instead of being a bump, you've hole punched it through.

Nigel - Yes. That goes into the computer and then you'll have another tape where you've typed data in that you need to analyse.

Graihagh - So, that goes into the machine. The machine does some magical maths I assume.

Nigel - Well, the maths actually isn't really so magical. The key thing about computers is they very rarely do anything complicated but they do complicated things by doing simple instructions, lots of them.

Graihagh - Given that lots of people are reconstructing EDSAC. I wonder what happened to it in the first place.

Nigel - It was very unceremoniously dismantled and sold off as scrap metal. Some people did actually take them away as bookshelves.

Graihagh - Someone at home has got EDSAC as their book shelf. Why are you going about completely reconstructing it?

Nigel - Before digital computers existed, there was no need to programme because no one had the concept. Once they existed as Maurice Wilkes said, "Now, we've got EDSAC. Now, we need to learn how to use it. i.e how to programme it." Well, that was the beginning of software so that makes it very important. The second motive for it is the education value. When school children come to the museum, beforehand, they will be able to write programmes for EDSAC and when they come to the museum, it will run their programme, print out a result, and they can take that home with them. They will be programming at the nuts and bolts level of computing. That's incredibly important.

Graihagh - I think especially since so many people are out of touch with - I mean, I certainly have no idea how my computer works yet I rely on it day in, day out.

Nigel - You don't need to. My view is that in the 21st century, computer literacy is as important as learning to read and write, and do arithmetic.

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