donj writes: IN 1995 Joseph Bower and Clayton Christensen, two researchers at the Harvard Business School, invented a new term: "disruptive technology". This is an innovation that fulfils the requirements of some, but not most, consumers better than the incumbent does. That gives it a toehold, which allows room for improvement and, eventually, dominance. The risk for incumbent firms is that of the proverbial boiling frog. They may not know when to switch from old to new until it is too late. The example Dr Bower and Dr Christensen used was a nerdy one: computer hard-drives. But unbeknown to them a more familiar one was in the making. The first digital cameras were coming on sale. These were more expensive than film cameras and had lower resolution. But they brought two advantages. A user could look at a picture immediately after he had taken it. And he could download it onto his computer and send it to his friends. Fourteen years on, you would struggle to buy a new camera that uses film. Some of the leading camera-makers, such as Panasonic, are firms that had little interest in photography when Dr Bower and Dr Christensen published. And an entire industry, the manufacturing and processing of film, is rapidly disappearing. Substitute "car" for "camera" and you have a story that should concern thoughtful bosses in the motor and oil industries.