Grace Hopper, who became a "coder" (or programmer) in the 1940s, was one of the great pioneers of the computer age. In 1934 she had been the first woman in Yale's 233-year history to graduate with a doctorate in maths. After Pearl Harbor, she worked on "a new type of secret weapon that could change the outcome of the war". The Automatic Sequence Controlled Calculator was 8ft high, 51ft long and had 530 miles of wiring. As well as calculating rocket trajectories, this "electronic brain" was used by the Manhattan Project scientists to build the atomic bomb. But it was in the 50s that Hopper invented the key software technologies that paved the way for today's computer languages. It was her genius for programming and her formidable powers of persuasion that prompted government agencies and corporations to agree on a common business programming language: Cobol. Beyer's meticulously researched biography shows how Hopper was one of the first to realise that software was the key to unlocking the power of the computer.