We learned this week that you'll be able play old Xbox 360 games on the Xbox One, a move that drew huge cheers from gamers at E3 2015.

Fans weren't the only ones surprised by Microsoft's concession to offering backward compatibility. Shuhei Yoshida, the president of Sony's Worldwide Studios — the guy in charge of securing games for the PlayStation console — was shocked by the announcement, too.

Backward compatibility has been a highly desired feature for both Sony's PlayStation 4 and Microsoft's Xbox One. There are less than 200 games available for each of those consoles, compared to the 1,000-plus games available for those consoles' predecessors. More games to play means happier gamers.

Yoshida told Eurogamer that he "didn't think [backward compatibility] was possible" and that Microsoft must have put "lots of engineering effort" into making it work.

Unlike previous generation consoles like the PS3 and Xbox 360, which used custom CPUs and GPUs, the guts of the PlayStation 4 and Xbox One have x86 PC-like architectures. The two are completely different animals. PC-like architectures let developers easily program on their PC development kits and bring them to the new consoles without needing to downgrade and optimize their software as much to run on punier hardware.

Adding Xbox 360 games support to Xbox One was definitely no easy feat for Microsoft. The company is using pure software emulation for the feature; in other words, the Xbox One will use software to replicate the Xbox 360's hardware.

As anyone who runs Windows through software emulation inside of Mac OS X can tell you, the function is very taxing on the CPU and GPU. More often than not, emulating hardware with software is never as glitch-free and smooth as running it natively.

While there will only be around 100 Xbox 360 games playable on the Xbox One at launch, Microsoft says it's working on adding many more to that list. It's just a matter of working with game publishers to get clearance.

So the question was on the tip of many tongues at E3: What would Sony's response be? The PS4 is more powerful than the Xbox One, so would Sony counter Microsoft's backward compatibility with the ability to play old PS3 games?

Yoshida says it's unlikely. "It's going to be super challenging to do so… but we have no plans."

Instead, Sony is taking a different approach: streaming. PlayStation Now streams a limited library of PS3 games to the PS4 for $20 (one month) or $45 (three months). Neither is cheap, especially if you already own a stockpile of PS3 games and don't want to shell out for the mere ability to play them.

Let the battle for the living room rage on.