We live in a digital age, within a digital economy, continuously engaged with digital media. Digital encoding lies at the heart of our contemporary mobile-obsessed, information-heavy, media-saturated world, but it is usually regarded – if it is thought of at all – as something inaccessible, virtual or ephemeral, hidden deep within the workings of our computers, tablets and smartphones. It is surprising that, despite the profusion of books on the history of computers and computing, little has been written about what makes them possible. So what exactly is 'the digital'? Where did it come from? What do we actually know about it? Robin Boast tackles these fundamental questions in The Machine in the Ghost  – and uncovers some very surprising answers.