Microsoft's most eye-catching E3 2015 announcement was the addition of backwards compatibility to the Xbox One. It means some Xbox 360 games will be playable on the console.
When it made the announcement, Microsoft used BioWare's action role-playing game Mass Effect to demonstrate the technology.
"It was surprising," Sony Worldwide Studios boss Shuhei Yoshida told Eurogamer editor Oli Welsh when asked for his reaction.
"I didn't think it was possible. There must be lots of engineering effort. They talked about 100 games, but what kind of games will be included? Is it smaller games or big games? We don't know."