EDSAC computer rebuild

Reconstructing the early electronic computers

Image credit: Getty Images

Reconstructions of early electronic computers are giving us new insights into how they worked and the software that ran on them.

Computer science is well-established as a field of academic study, but its initial development went almost unnoticed in the midst of the Cold War and social movements such as Flower Power and feminism. However, it’s done more to transform the way we live and work more than anything else. Albeit a defining feature of modern society, the electronic computer and the scarcity of actual apparatus from the early days has left gaps in our knowledge of how early hardware and software really worked. It also means that the full extent of the contributions made by computer pioneers to the rise of information technology remains incomplete.

Growth of interest in technology heritage has spurred a succession of early computer restorations and reconstructions, especially in the UK and Germany. This has been motivated in part by a desire to raise awareness of the IT industry’s lineage, and to honour past pioneers of computing whose work has been undervalued because so little evidence of their achievements survives.

“Reconstructions and rebuilds [of early computers] can add an alternative and fascinating level of understanding,” says Dr Jochen Viehoff, director at the Heinz-Nixdorf MuseumsForum in Germany. “A deep understanding of the basic computer functionality requires [an understanding of] the lowest level in terms of logic gates, transistors or – more historically – relays and valves. A hands-on approach to this level of electrons, signals and physics can improve the learning process significantly.”

The Heinz-Nixdorf MuseumsForum’s recent reconstruction of part of the US ENIAC (Electronic Numerical Integrator And Computer) system from 1946 uses original components combined with contemporary technology to represent a scaled-down recreation of two original ENIAC accumulator units. The interactive exhibit allows visitors to try their hand at ENIAC programming and better understand complexities faced by its original operators 70 years ago.

Early computer reconstructions “can help put today’s computer technology into a historical perspective/framework,” says Silicon Valley veteran Robert Garner, who oversaw the IBM 1401 Demo Lab restoration/exhibit at the Computer History Museum in California. Looking at how far computers have come in the last 50 years can help technologists forecast how far computers might advance in the next half a century, Garner adds.

Although many aspects of early computing – theory and practice – were recorded in books and journals, the possibility that future generations of technologists and engineers would be interested in their outdated computers, and the programs they ran, was not of overriding concern to experts back in the day. They were more preoccupied with developing better versions of their inventions, and seeing them change the world as computers moved out of the rarefied realms of military R&D and academia, and into business and applied sciences.

‘Giant brains’ of the 1940s and 1950s were usually one-offs or limited editions at best, and often devised and discarded by project groups with no formal archival procedures. When they reached the ends of their useful lives, they were decommissioned and dismantled. Some components would be recycled into successive versions, other parts might have been boxed-up and forgotten about while a few pieces were kept as souvenirs. Everything else was discarded.

Programs and system documents – code, chassis blueprints, circuit diagrams – were similarly thrown away or haphazardly stored.

Since it opened in 2007, the UK National Museum of Computing, working with the Computer Conservation Society, has facilitated several restoration and reconstruction projects: they include the Harwell Dekatron (WITCH), the ICT 1301 (Flossie), and, most famously, wartime codebreaker Colossus. This year sees the culmination of one of the Museum’s flagship conservation programmes, the EDSAC Replica Project, which has reconstructed one of the most important digital computers built and operated in the UK in the mid-20th century.

Due for completion later this year, the reconstruction of the EDSAC – Electronic Delay Storage Automatic Calculator – holds particular significance in the evolution of information technology because, in several respects, EDSAC started the scientific and business computing that has shaped human discovery and economic progress over the last six decades.

Built in the Cambridge University Mathematical Laboratory by a team led by the late Professor Sir Maurice Wilkes, EDSAC was the first practical general-purpose stored program electronic computer. One goal of the Replica Project is to build an authentic working reconstruction of the EDSAC machine and run programs on it as was done when the original was demonstrated. The project also aims to provide a tangible demonstration of the achievements of the team that devised and operated it between 1949 and 1958.

Wilkes’ team worked to a specific brief: to provide ‘mechanical’ aids that would enable mathematicians, engineers and scientists at the university to perform complex, time-consuming calculations for a variety of fields of research and study, and alleviate the necessity for research workers to perform arduous computations using mechanical desk calculators and mathematical tables. Wilkes’ vision was to create a common resource which could be used by a wide range of university researchers, instead of the few ‘high specialists’ who tended other early electronic computers. He wanted a computer that “was accessible and practical”.

EDSAC soon established its reputation as an invaluable computational resource for researchers at Cambridge University during the early-to-mid 1950s. Arguably, this ‘service model’ could be viewed as a primitive form of the computer time-sharing concept which, decades later, developed into what now forms the basis of cloud computing: versatile shared compute and storage resources.

“As director of the Mathematical Laboratory, Maurice Wilkes was responsible for providing ‘computing services’ to the University,” says Martin Campbell-Kelly, professor at the University of Warwick’s Department of Computer Science. “Before EDSAC, this meant mechanical calculators of different kinds, and advice on numerical methods for hand or calculator use to solve practical problems from science and engineering. The scale of problems that could be solved by hand or calculator was limited, so when Wilkes was introduced to the possibility of electronic computers he was keen to build one for Cambridge University to use. His goal was entirely practical – build a simple machine quickly, and see how people used it, in the expectation it would be replaced by improved designs in the light of experience.”

A core aspect of the contribution made by early computers to scientific advancement was the huge acceleration of basic calculations necessary for several fields of research. These days, such step-changing acceleration would be jargonised as a ‘paradigm shift’, but back in the 1950s it was hailed as a labour-saving marvel. Yet it wasn’t just that EDSAC processed big numbers faster and more accurately than humans. The opportunity that computers like EDSAC offered also influenced the way in which their end-users thought about their requirements and approach to work.

The change for academics was they could process much larger amounts of data than was possible by hand or mechanical methods and get the results more quickly, says Campbell-Kelly. “Also, EDSAC didn’t make errors – it either worked or didn’t,” he continues. “It was rare for programs to run and produce incomplete results, and if you were really concerned it was fast enough you could rerun the program a number of times to check for consistent answers.”

By using numerical techniques, academics were less restricted in the types of mathematics they could use to model physical phenomena, because numerical techniques can be applied to solve equations that don’t have analytical solutions. Campbell-Kelly adds: “Similarly, a computer could quickly search for optimal parameter settings, and so forth. In turn, this allowed for new approaches to science.”

The Replica Project is not the first attempt to resurrect EDSAC: the EDSAC simulator – software ‘evocation’ of the original with a user interface – has all controls and displays of the original machine, and the system includes a library of original programs, subroutines and debugging software.

“Where hardware cannot be recreated, a thorough software reconstruction can still teach valuable things about the machine in question, and it allows the software to be re-run from the time – [and thereby ensures that] the algorithms survive,” says artist and computing historian Dr David Link. “Software emulation has also sometimes been a very good first step towards a physical reconstruction, as in the case of Colossus. Re-running scientific software is important because it allows re-evaluating results of scientific experiments in the past.”

Although simulators can ‘run’ programs in a virtual environment, they cannot convey a fully authentic recreation of how it was to operate computers like EDSAC as physical entities, claims EDSAC project leader Andrew Herbert. Practicalities of handling paper tapes [the physical media on which programs are stored], checking them, and reading them in to the machinery, provide additional insights into how far we have come with regard to user interfaces. Herbert says: “Using the replica will recreate the hands-on experience of putting programs together on [punch hole] tape, operating the machine, keeping it running, doing fault diagnosis when it fails, and so forth. Unless set on ‘real-time mode’ the simulator runs faster than [the physical] EDSAC, so [when the replica is operational] its users will have to learn patience. They’ll be pushing real buttons, and looking at real CRT monitors, rather than driving a modern display.

“They will also get to experience how hot it was in the EDSAC room, especially in the summer: it consumes around 11kW of electric power, most of which is emitted as heat.”

EDSAC programs written to help Cambridge researchers could be thought of as ‘applications’, although they were usually to a specific requirement. As operations progressed over time, parts of programs could be re-used for different requirements. EDSAC was the first computer to have a library of subroutines and an assembler built into its program loading system.

“There may [still] be some yet-to-be-discovered test programs or programs for some of the later experimental facilities – such as magnetic tape – which will take both the simulator and the replica EDSAC by surprise,” Herbert suggests.

Another area where early computer recreations can add to our understanding is origins of software applications. According to Link, it is possible that program writers of the early 1950s developed (albeit in nascent form) some of the standard task-oriented applications now commonplace on our PC desktops – including applications that are often assumed to have been put together by computer companies of the 1960s and 1970s.

“The usage of early computers was certainly mostly science-oriented, although there were programs for the calculation of wages, for example, or life assurances,” Link says. “It depends on the type of application. You will not find a word-processor program on the Ferranti Mark 1 [for instance; however,] for all scientific disciplines like meteorology, engineering, x-ray crystallography, [and more], we find quite advanced software.”

Historian David Link’s art gallery installation ‘LoveLetters_1.0’, based on a replica of a 1951 Ferranti Mark 1 computer with reconstructed software that generated texts to express and arouse emotions, won the 2012 Tony Sale Award for computer conservation. LoveLetters_1.0 executes recovered software by computer scientist and programming pioneer Professor Christopher Strachey (1916-1975). In his research, Link discovered that some of Strachey’s Ferranti Mark 1 code had been sitting in archives, such as the Bodleian Library in Oxford, unexamined for 60 years, and was not documented to the extent that we can fully understand how it performed.

Link has argued that the history of computing will have to be revised if surviving early programs developed by pioneering software engineers for the Ferranti machines, and their close successors, can be made to run again on reconstructed hardware: “In other cases, we have some documentation about programs that have not survived. Most engineers involved, that might be able to cast light on the software’s purposes, have now sadly passed away.

“Some histories assume software for scientific and business applications was first developed by big commercial computer giants of the later mainframe era – but that is not entirely the case... My discoveries lend support to the suggestion that pioneering software engineers connected to Manchester University’s computing department [such as Strachey, for instance] were arguably the ‘first to market’ with customised programs. But we need more rebuilds so that we can validate these claims with standard scientific rigour.”

EDSAC’s wider significance in the establishment of the UK computer sector past and present is perhaps more concretely evidenced as a progenitor of business software applications via the LEO I computer, first used by caterer and food manufacturer J Lyons & Co in 1951. J Lyons executives had shown unique foresight with their realisation that electronic computers could do much to improve the administration of large and extensive business enterprises, such as their own.

Impressed by EDSAC, J Lyons invested some £3,000 – equivalent to around £75,000 in 2017 – in the EDSAC project (and seconded an electrical engineer to help speed-up development), with a view to using it as a prototype for its more commercially-oriented solution. Following EDSAC’s successful commission, J Lyons constructed its own purpose-made computer based on it – LEO (Lyons Electronic Office) I – which became the first computer designed specifically for company back-office applications.

According to IT pioneer and businesswoman Dame Stephanie Shirley: “Business computing is dead simple compared with the science and engineering calculations that computers had previously done – but there’s an enormous amount of it, and it is [also] time-critical.” LEO was “not only the very first business computer, but its designs also had a massive influence on later machines”, Shirley added, speaking at a LEO commemoration in 2016. “Basically, it seeded the British computer industry.”

Cambridge’s problem-solving workhorse

Calculating (...but not cool)

EDSAC was a reliable machine that did significant work through its nine-year operational lifespan. Like all computers of its era, it was based on 3,000+ thermionic valves which generated 12 kilowatts of heat, along with warmth from other components such as teleprinter and CRT screens. Its construction was led by project chief engineer Bill Renwick. Research student David Wheeler, meanwhile, was responsible for many features that made the machine practical for non-specialist users.

The machine ran its first program on 6 May 1949, after which EDSAC ran 35 hours a week on average. During daytime operations, engineers managed problems as they occurred. In the night-time operations, approved users could work on the computer, but if it malfunctioned they had to wait until morning before problems would be remediated.

EDSAC was modest in terms of today’s computing power. There were only 18 operation codes and initially just 512 words of memory, later extended to 1,024. Instructions were executed at a rate of approximately 650 per second. Input was by punched paper-tape, and output by teleprinter.

It’s been estimated that EDSAC introduced a 1,500x productivity increase to Cambridge University research projects that it worked on: researchers became able to solve problems that were previously considered impractical or impossible.

A substantial number of users had the scope of their research transformed and extended through increase in computer power that EDSAC provided. Among them were future winners of three Nobel Prizes – John Kendrew and Max Perutz (Chemistry, 1962) for the discovery of the structure of myoglobin; Andrew Huxley (Medicine, 1963) for quantitative analysis of excitation and conduction in nerves; and Martin Ryle (Physics, 1974), for the development of aperture synthesis in radio astronomy.

(Source: National Museum of Computing)

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