The Paris Review has an interview with Gibson in which he explains how her arrived upon the idea of cyberspace. I knew the famous story about seeing the Apple ad at the bus stop, but in this he puts the whole process together:
I was walking around Vancouver, aware of that need, and I remember walking past a video arcade, which was a new sort of business at that time, and seeing kids playing those old-fashioned console-style plywood video games. The games had a very primitive graphic representation of space and perspective. Some of them didn’t even have perspective but were yearning toward perspective and dimensionality. Even in this very primitive form, the kids who were playing them were so physically involved, it seemed to me that what they wanted was to be inside the games, within the notional space of the machine. The real world had disappeared for them—it had completely lost its importance. They were in that notional space, and the machine in front of them was the brave new world.
The only computers I’d ever seen in those days were things the size of the side of a barn. And then one day, I walked by a bus stop and there was an Apple poster. The poster was a photograph of a businessman’s jacketed, neatly cuffed arm holding a life-size representation of a real-life computer that was not much bigger than a laptop is today. Everyone is going to have one of these, I thought, and everyone is going to want to live inside them. And somehow I knew that the notional space behind all of the computer screens would be one single universe.
Unfortunately, in order to read the whole interview you have to buy the entire issue in print. Update: The whole interview is now available.