Emulation is key to Microsoft's Xbox backward compatibility story

Microsoft has built an new emulator for its Windows-powered Xbox One console to allow backwards compatibility.
Written by Mary Jo Foley, Senior Contributing Editor

One of Microsoft's biggest announcements at the E3 show (so far) is that the company will provide the ability to run Xbox 360 games on Xbox One -- theoretically making the Xbox One console more interesting to Xbox 360 holdouts who didn't want to abandon their existing game collections.

In some ways, Microsoft's backward-compatibility strategy isn't a total surprise. Microsoft execs signaled at Build 2014 that Microsoft was investigating how to build an Xbox 360 emulator that would allow gamers to do just that. (Official later stepped back from that statement.)

It looks like that emulator work panned out. Starting today, June 15, Xbox Preview members can start testing the first wave of Xbox 360 games on their Xbox Ones. Microsoft officials said that the backward emulation capability would be available for everyone this holiday season (meaning fall 2015).

I'm not a gamer, but I am interested in anything Windows-related that powers Microsoft and third-party hardware, including gaming consoles, work.

Unfortunately, Microsoft's Xbox.com site does little to explain how the backwards compatibility works.

The site notes that digital titles users already own are part of the "Back Compat game catalog" and will automatically show up in the "Ready to Install" section of Xbox One. For disc-based games that are part of the Back Compat game catalog, gamers can insert the disc and the console "will begin downloading the game to your hard drive." (After the game downloads, users still need to keep the game disc in the drive in order to play.)

There was a bit more information on that Xbox.com site about backwards compatibility, which now seems to have been removed. In a now-absent "Trending Questions" section, Microsoft acknowledge it was a new emulator that makes this work.

From the Q&A:

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.

I asked Microsoft officials for more information about the emulator and was provided with this statement by a spokesperson:

"What we did was essentially built a virtual Xbox 360 console entirely in software. So when you launch a game via Xbox One Backward Compatibility, you'll see that the game first starts up a virtual Xbox 360 console, then launches the title. The work is ongoing as each title requires individual packaging and validation work to enable that virtual console capability, but we're committed to continually rolling out new titles each month."

I've asked for more specifics about the emulator, but so far, officials aren't providing information beyond that statement.

This isn't the first time Microsoft has built an emulator to enable backward compatibility for Xbox. A decade or so ago, a team inside the company built an emulator enabling original Xbox games to work on Xbox 360.

The Xbox One operating system -- really three operating systems in one -- is based on the Windows 8 core. Microsoft plans to update the console with the Windows 10 core some time in the coming months, and possibly this year.

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