Computers are the most versatile machines ever invented, and the same piece of hardware can be used for thousands of different purposes. They can create virtual worlds with extraordinary realism, play chess better than almost any human, and even isolate a person’s position to within a few metres anywhere on the planet. What makes this possible is something that cannot be seen, felt or touched, but without it the digital revolution would never have happened. Professor Bishop investigates the software that brings a machine to life, and turns it into a phone, a music player, a game, or any number of other devices – including ones not even imagined by the creator of the hardware.