This article proposes that the modern computer screen is derived more from the radar screen rather than, as might be expected, the television screen, which has important ramifications for how the computer has developed and been understood. These ramifications are being obscured by the current drive towards the ‘convergence’ of television and computing. This article traces the modern computer screen back to the development of nuclear early warning systems in the 1960s (based on the British radar networks of the Second World War) and to the work of ex-radar operator Douglas Engelbart and his Augmentation Research Center at Stanford Research Institute, both of which were instrumental in how we now understand and use computers as ‘real-time’ machines.