Volunteers build replica of Edsac .’s oldest general university computer

The National Museum of Computing in Bletchley, England, is building a replica of the first general-purpose computer that stood at the University of Cambridge in 1949. The Edsac was the first computer that didn’t serve a very specific purpose, as was common at the time. .

Rebuilding such a piece of electrical engineering from 1949 is no mean feat. The way the electronics are connected in particular causes many problems with the project, the BBC reports. Initially, the rebuilding volunteers used old photographs to find out how the computer’s schematics worked and how the 3,000 electron tubes communicated with each other. Work on the Edsac of Electronic Delay Storage Automatic Calculator is progressing steadily, and project leader Andrew Herbert hopes the computer will be up and running by spring 2016. The original computer was scrapped in the 1950s and sold in parts at auction. A part of the computer was discovered in February this year in the United States. The owner of the Chassis 1A part donated it to the project.

Chassis 1A – Source: National Museum of Computing

Edsac was the first computer that researchers could actually use as a scientific calculator. The team that built the machine wanted to make programming as simple as possible, Herbert told an Australian radio station in an interview. The machine had no transistors, let alone printed circuit boards or integrated circuits. It was an electronic machine using electron tubes and took up about two square meters of floor space. The whole was made up of about 140 boards with electronics. All together it weighs about 2000 kilograms and consumes 11 kilowatts.

The machine had a kind of memory, so-called delay line memory, which consists of tubes containing mercury. Information was stored in the mercury using sound waves. This technology is not used in the rebuilt computer because it is quite unstable and mercury is highly toxic. All that electronics accounted for a thousand words of memory, equivalent to about 3 kilobytes. The computer could handle 650 instructions per second. Compared to a student with a slide rule, the computing power of the computer was about 1500 times greater. This allowed Cambridge to perform some science that would not have been possible without a computer, such as X-ray crystal structure analysis to find out the structure of hemoglobin in blood. Astronomers used it to perform aperture synthesis. The latter is combining signals from different telescopes to simulate a larger telescope.