So we're at the National Museum of computing and what we're doing here is building a reconstruction of Cambridge
University's first computer which is called the electronic delays storage automatic calculator
It's the important computer because it was the first one that was actually built for people to use to solve problems
It helped three groups of scientists in Cambridge win their Nobel prizes
And it was the first machine for which there was a programming system of the kind that a a modern programmer would understand
There was a library of useful subroutines you wrote in a symbolic assembly code
before that people program machines by feeding things in through switches or just typing in the binary code of
Instructions the first machine was scrapped to make room for its successor
physically very large a few bits and pieces ended up in museums and that most of it was lost and
Indeed very few of the circuit diagrams and none of the mechanical design drawings were kept all that were retained were
photographs and high-level descriptions and so in doing the reconstruction
we've had two friends that clear analyzed those photographs and work back from those two the the
Circuits inside the machine all the people who worked on it had a background on
working in radar during the Second World War and one of the key things about
Radar is it?
Transmits pulses that bounce off an aircraft or a ship and reads them back and of course pulses of the basis of how a computer
works in terms of counting
So they're already from their radar work
understood how to make pulses how to amplify them how to count them how to compare numbers
Represented as sequences of pulses
so they were on the threshold of computing and they use their expertise to build the
EDSAC machine the challenge really has been to get back to the original design
Obviously the photographs are very helpful, but they were taken throughout the nearly ten years that the machine operated
And they improve the design a lot over that time
So knowing which photographs relate to the early machine is difficult in terms of making the circuits work
This is a machine that comes out of a more analogue view of electronics
Not such the clean ones Zero's that were used to in the transistor world and so it's a different way of thinking about electronic circuits
That's certainly given us some challenges
It's really helpful that in the volunteer team we have people who worked on some valve
computers at the start of their careers or they worked on valve base radar and radio
systems for the Air Force for example and so we're tapping into what they learnt as college students each of these units has got a
Set of fingers inside if you come on this side you can see
The project is now nearly 5 years old and the early stages were very much a feasibility study
Doing a lot of research finding out
What documentation was around and?
To see what we could still obtain in the ways of it these these valves and so forth it turns out
They are still really obtainable because they were used in things like military radar
There's a lot of surplus stuck around and there are companies who still that stuff, then the next challenge was to recruit a volunteer team
Particularly people who have the expertise to be able to recreate the designs of the circuits, and we're very fortunate
We've got four or five people with their expertise
The total volunteer team is now about 20 and the rest of the team are very much concerned with the the construction
Compared to the pioneers we have a great advantage we can use modern computers design EDSAC
So all this metal work is done using computer-aided design
And we send the computer drawings to a manufacturing company that happen to be in Cambridge
And they make all the parts to our drawings whereas their site this and all would have been handmade in the university workshops
Similarly with the circuits all the circuits. We have and
schematics of those on the computer we can use computer simulations
To check out the design of the circuits and in fact check out the logic of the whole machine
So we know we're building something that will eventually work. That wasn't a luxury that maurice wilkes and his team had in Cambridge in
1947 when they started many of the the basic
Ideas you needed to generate pulses and so forth have been established in the world of radar
the challenge was thinking about how to use those to build something that actually computes and
Scaling up to a system this large there
3000 vowels in EDSAC, which makes it a very large and very complex system and so thinking through a
Machine that was that large that had lots of different functional parts doing different jobs. That was really the challenge
it was a step up in complexity, but in terms of the basic circuit elements a
Radar engineer of the 1940s would recognize the the techniques we're using we talk about things like cathode followers
flip-flops
That's a word that still exists in modern electronics those would all been things that an engineer of that time would have been aware of
But we've done
So the big difference in EDSAC is a flip-flop takes seven of these vowels, and so if you think about a
Microchip in a modern computer. That's got thousands. Maybe millions of flip-flops in it on EDSAC
You can get about three flip-flops on one shelf of electronics, so there had to be much more economical in their design
So it's act was very much designed for numerical computation in the university to help physicists and mathematicians
Prior to EDSAC they had to rely on hand calculators there were a few manual
Mechanical calculators, they could use, but that limited the size of problem. They could work on just because it took so long to
Work on a large matrix of numbers. It's that was so much faster about
1,500 times faster, they could work on much bigger problems and
That changed the kind of science that could be done so one example was Radio Astronomy
What?
Edsac allowed martin royal to do was to put a lot of small radio telescopes in a field
collect data from those small telescopes
Which are easy to build but?
Then with the power of edsac had all that data together as if it was a radio telescope the size of a field another
area where edsac helps
Was what's called x-ray?
Crystallography which is working out the structure inside atoms and molecules head sacks input and output was very basic
It was five whole paper tape that was really the established medium for inputting any kind of data
There's what was used by the telegraph system and the telephone systems
So you fed your data in your programming is 5 hold paper tape and your answers came out on a online
teleprinter as a table of numbers and
Because machine time was so limited and so valuable you didn't waste time printing pretty headings or laying things out very neatly
You kept everything very tight and very simple because the memory of the machine was so small for a large
Calculation you might break it into three pieces the first piece would read the data into the main memory
Then you'd load a second program
That would do the calculation on the data in the main memory
And then you load a third program that will pump the results out of the memory and put them on the telly printer for you
And so they had to be quite cunning because I though it was a huge advance in its time
It was in many ways quite a limited machine the team who built it
realized that making it easy to program the machine was going to be one of the important factors influencing its usefulness and
So they very early on established a library of standard subroutines that packaged up calculations for useful mathematical
Functions that packaged up ways of organizing work in the machine and doing the input and output
So typically once you knew what your numerical problem was you pick the right library routines?
You wrote a bit of what these days
We call glue code to put those together
And then you had a working program and so none specialists or people from other areas like physics engineering mathematics
Came to use EDSAC from the earliest days they decided they weren't going to have
specialists edsac programmers to solve people's problems
Rather than they would teach people how to use the machine
Because that was a more scalable way of getting the computing done in terms of running edsac the user turns up with their paper tape
And we don't quite have it yet, but there'll be a start button there
you press the start button your paper tape reads in and
hopefully the teleprinter starts chattering the need obviously with a valve machine like this an
Experimental machine is for engineers to maintain it and so the mathematical laboratory has an engineering crew any working dough
I'm sure there'll be three or four available and you rely on them to check the machine at the start of the day
The the way the machines memory works it needed regular adjustment and so there be engineers a to help you with that
They they worked as it were a normal office dirty with
engineers in support and indeed later on there was an operator who ran programs for people just to get the
Faster flow and work through the machine, but if you were an approved user you could work the machine at night
Until it went wrong, and then you had to kind of walk away and leave it for the engineers to fix in the morning
I'm sure there was
Certainly if you taught some of the people use the machines in those early days there are all kinds of tales and little tricks
apparently in the early days the way you reset the memory was by wetting your finger and touching a
terminal to earth that part of the machine probably something modern health and safety wouldn't quite approve of
Some of these vowels are coming out of boxes that are labeled
1943 so they've not been used they were made in the nowadays to having Macintosh and Windows with everything
provided for us and layers of software in the early days
You were right near a bear mat arm system in the first Archimedes would run reliably well above 100 degrees C