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This is basic stuff folks. Microsoft didn't release the backward compatibility on day one for strategic reasons, not technical ones

Not true.

"Implement or emulate

There are effectively two ways to provide compatibility with previous consoles: through hardware implementation, or via software emulation of the old machine. In the former case, it involves actually including some of the chips from the old machine in the new machine. The Nintendo Wii, for example, was in many ways just a more powerful version of the older GameCube, so backwards compatibility was reasonably straightforward – indeed the Wii originally had GameCube controller sockets and two memory card slots. It was like a GameCube in disguise. The PlayStation 2, meanwhile, had the original PlayStation chipset built in, so it ran pretty much any PSone title – and when that chip wasn't being used for backwards compatibility it doubled as an input/output processor, which was pretty canny.

"What's different now is the increased complexity in hardware and software, and heat issues," says veteran coder and game designer Martin Hollis. "The best way to support your old console, in terms of broadest support of all old games, is to actually include the hardware of the old system inside the new one. CPU, GPU, sound chips, ideally the whole caboodle.

"This works well enough when you look at the price list for components, as the old chips have become cheap enough to include without bumping the cost of the new system. Sadly though, with the high frequency clock rates (GHz), designing your board to incorporate the entire old machine is not easy or cheap, and worse, it will emit just as much heat as the old system did on it's own. Heat is a big factor with modern system designs and you do not want to add 100 watts to your output, and another jet turbine style fan."

So as new hardware becomes more complex, the inclusion of older chips and processors becomes more expensive, and with margins so tight (manufacturers often make a loss on new machines anyway), it's an easy feature to jettison. Indeed, although both the original versions of the Wii and the PS3 included old feature-sets in the architecture, later versions ripped these out to cut down on costs and allow for price drops.

Virtual boy

So what about emulation? This involves running a program on the new console that effectively pretends to be the old machine so that it can play classic games. Nintendo, for example, offers its Virtual Console service for the Wii and 3DS which allows owners to download and play classic Super Nintendo, Game Boy and even Sega Mega Drive titles in their original form.

Once again, however, the problem with emulating more recent consoles is technological advance. "It was when the PS3 tried to emulate the PS2 that the increase in technology began to present problems," says developer Byron Atkinson-Jones, whose new game Blast 'Em has just been released. "Like the PS1, the PS2 had a single processor but the graphics system was a lot more complex, allowing for parallel processing, which meant it could run more than one bit of code at a time. You can emulate this on the more modern processors but you have to get the timing between the true hardware-based parallel processing and the software emulated version exactly right. And that timing would also have to take into account the differences between the territory versions, i.e. a game running on PAL or NTSC. Along with other factors that might be enough to break a game."

And timing is not the only issue – the increasing adaptability of the hardware itself is also causing problems. "It's complexity versus schedule," says Hollis. "If your emulated graphics processor is programmable (as PS3 and Xbox 360 are) that creates a huge explosion of possibilities to emulate and test – easily trillions of cases. We are talking large possibility spaces here. No way you are going to be able to emulate all the games, and do the job in a rush. If you had ten years, well maybe.

"The second piece of bad news is performance headroom. To emulate an old system's hardware in software you need a system which is significantly more powerful, I'd say ten times more powerful is a good rule of thumb. This current generation is simply not that much more powerful than the last, especially in terms of general purpose compute. Moore's law is basically over for CPUs, and has been for around five years. That means new machines do not have the power to emulate last generation in software."

Cloud saves the day?

So does this mean we'll never see old games on new consoles? Of course not. Nostalgia sells, after all. Next year we'll see the launch of the Gaikai service on PlayStation 4, which will allow gamers to live stream games over the internet from a central server. Sony has already promised to make key PlayStation 3 titles playable via this platform, which removes the need for the console itself to perform the emulation. Of course, this won't let you play your old PS3 discs on your PS4, but it will at least let you re-discover (and of course, re-pay for) old classics. Meanwhile, Xbox One could theoretically perform the same service via cloud computing, but the company has expressed doubts that current broadband speeds would be able to provide a playable experience.

PS4 and Xbox One: so why aren't they backwards compatible?

"What is Xbox One Backward Compatibility and how does it work?

Xbox One Backward Compatibility is an Xbox 360 emulator that runs on Xbox One and is used to play Xbox 360 games.

If it’s actually emulation, why are you calling it backward compatibility?

We call it backward compatibility because gamers can play select Xbox 360 games on the Xbox One. However, referring to this functionality as an emulator is more accurate from a technology perspective since the Xbox One is not technically reading and playing the 360 game off of a disc.

When will it be available?

The Xbox One Backward Compatibility Beta is available starting June 15 for Xbox preview members. The program will launch broadly for fall 2015.

Previously, you said back compat wasn’t possible on Xbox One. How is it possible now?

We didn’t know if we could do it, but we were inspired by our fans, and thanks to the dedication and determination of a group of brilliant engineers in our platform team who developed Xbox One Backward Compatibility, we made the impossible, possible."
Microsoft Built An Xbox 360 Emulator Into Xbox One To Bring Backward Compatibility