Three years ago today, on January 27, 2010, Steve Jobs stood on a stage in San Francisco.

First he talked about how Apple invented the modern laptop in 1991 and revolutionized the smartphone with the iPhone in 2007.

Then he asked: "Is there room for a third category of device in the middle? Something that's between a laptop and a smartphone?"

After trashing an existing category of devices – the netbook – Jobs's tone of voice changed. It grew hushed and fervent.

And then he said: "We think we've got something that is. We'd like to show it to you today for the first time. And we call it…the iPad."

The world hasn't been the same since.