EDSAC
In the aftermath of the Second World War, as Europe tended its wounds, a project was taking shape in the laboratories of Cambridge University. Maurice Wilkes and his team were designing a machine that would forever mark the history of automatic computation: EDSAC.
This automatic calculator with delay line storage, built between 1947 and 1949, bore no resemblance to the computers we know today. Bulky, noisy, power-hungry, EDSAC embodied the first practical application of von Neumann’s theories on computer architecture, a conceptual framework that still governs our current machines.
In the post-war British context, where resources were sorely lacking, building such a device was quite an undertaking. Yet the project was part of a rich tradition, with the codebreaking work at Bletchley Park and Turing’s ACE at the National Physical Laboratory. EDSAC’s distinctive feature lay in its general-purpose nature which, unlike its predecessors dedicated to specific calculations, was designed to be adaptable to all types of mathematical problems.
Its memory constituted a fascinating technical feat. Imagine tubes filled with mercury where ultrasonic pulses propagate, representing through their presence or absence the famous 0s and 1s of binary language. This “delay line memory” stored 1024 words of 17 bits each. The team had also designed miniature versions of these lines for the arithmetic unit’s registers, a solution as ingenious as it was elegant despite its practical drawbacks.
The microprogrammed control unit, another major innovation, physically separated the decoding of instructions from their execution. This architecture, encoded on 17 bits with a single-address format, included conditional jumps, a hardwired multiplier, and shift operations. Numbers were represented with a sign bit and a fixed point, to handle either short integers or near-double precision numbers using two memory words.
In May 1949, EDSAC performed its first public demonstrations, thus becoming the first operational computer based on von Neumann architecture. With its modest 650 instructions per second and 2 kilobytes of memory (a million times less than our current phones), the machine found its place in Cambridge’s scientific research.
The 1950s saw EDSAC at the heart of scientific advances. Rosalind Franklin used it for her work on DNA structure, while researchers in astronomy, economics, or linguistics trained in its use. A genuine computing community was emerging around this pioneering machine.
On the software front, David Wheeler created the first assembler on EDSAC in 1951, replacing tedious binary codes with mnemonic instructions. A few years later, Alick Glennie’s Autocode language foreshadowed high-level languages like Fortran or Algol. Libraries of reusable subroutines appeared, initiating the structured programming methods of the future.
EDSAC inspired other British universities for their own machines, namely EDSAC 2 at Cambridge, MOSAIC at Manchester. Across the Atlantic, the University of Illinois developed ILLIAC, directly derived from plans generously shared by Wilkes and his team.
EDSAC’s decommissioning in 1958, after a decade of loyal service, marked the end of an era but not that of its legacy. Without knowing it, EDSAC users were already manipulating the fundamental concepts we use daily: stored-program in memory, sequential architecture, instruction set, and subroutines.