Colossus and the Rise of the Modern Computer

Secrecy about Colossus has bedevilled the history of computing. In the years following the Second World War, the Hungarian-born American logician and mathematician John von Neumann, through writings and charismatic public addresses, made the concept of the electronic digital computer widely known. Von Neumann knew nothing of Colossus, and he told the world that the American ENIAC—first operational at the end of 1945, two years after Colossus—was ‘the first electronic computing machine’. Others familiar with the ENIAC and unaware of Colossus peddled the same message. The myth soon became set in stone, and for the rest of the twentieth century book after book—not to mention magazines and newspaper articles—told readers that the ENIAC was the first electronic computer. In 1971, a leading computer science textbook gave this historical summary: ‘The early story has often been told, starting with Babbage and . . . up to the birth of electronic machines with ENIAC.’ The present chapter revisits the early story, setting Colossus in its proper place. In the original sense of the word, a computer was not a machine at all, but a human being—a mathematical assistant whose task was to calculate by rote, in accordance with a systematic method supplied by an overseer prior to the calculation. The computer, like a filing clerk, might have little detailed knowledge of the end to which his or her work was directed. Many thousands of human computers were employed in business, government, and research establishments, doing some of the sorts of calculating work that nowadays is performed by electronic computers (see photograph 42). The term ‘computing machine’ was used increasingly from the 1920s to refer to small calculating machines which mechanised elements of the human computer’s work. For a complex calculation, several dozen human computers might be required, each equipped with a desktop computing machine. By the 1940s, however, the scale of some calculations required by physicists and engineers had become so great that the work could not easily be done in a reasonable time by even a roomful of human computers with desktop computing machines. The need to develop high-speed large-scale computing machinery was pressing.