Welcome to the EDSAC

1949: A Mechanical Brain

On the top floor of a rather drab building in a narrow Cambridge back street is an apparatus which seems to consist chiefly of a vast number of valves set in grey painted racks. ... this weird array of wires and valves is a "mechanical brain." It has just been completed and it is the most advanced in the world. It is probably the major scientific marvel of 1949 and although until now we have lagged behind America in mechanical brains this one puts us streets ahead.

This is how it works. First Mr Wilkes fed a strip of paper punched with holes into a "ticker-tape" machine. As the paper ticked through ... miniature television screens showed a row of green blobs ... then almost instantaneously a teleprinter nearby began to print rows of figures. That was all. There were no dramatic sparks, no dramatic flashes ...

There are not enough "brains" to go around at the moment, but a dozen would probably be sufficient for the whole country ... The future? The "brain" may one day come down to our level and help with our income-tax and book-keeping calculations.

But this is speculation and there is no sign of it so far.

- The Star, June 1949

1999: The Information Age

In the 50 years since the first output of the EDSAC, the growth in computer power, complexity and usage has been nothing short of extraordinary. However the development work involved in designing and building the EDSAC here in Cambridge remains a remarkable feat of engineering and early programming. Features of the EDSAC set a precedent for computer design and function that is still in evidence in contemporary computer architecture, whilst programming concepts such as subroutines and code libraries are now taken for granted.

The original machine vanished along with the University Mathematical Laboratory, and the Computer Science department of the present day would appear to be a world away from the early days of computing. However it is a measure of the rapid development of computers, and a testament to the skill of the early pioneers, that those who worked on the original project are still associated with the department.

50 years on it seems fitting that we should re-examine work of the EDSAC project, and more specifically make it available to a far wider potential audience than the original. Simulating the EDSAC is not only of historical interest, but educational to anyone involved with Computer Science. The increasing levels of complexity and abstraction in modern computers make it difficult to appreciate the roots of design decisions, and the operation of a stored-program computer at the most basic level.