The new 'backward compatible' Xbox games on PC run on an OG Xbox emulator inside an Xbox 360 emulator, and people have already used it to run other Xbox 360 games

First reported by Tom's Hardware, it's come to light that, not only are the four "Backward Compatibility on PC" original Xbox games released last week running on a double layer of Xbox console emulation, but savvy independent developers have already used those emulators to run other Xbox games on PC.

Developer Nathan on X, "The Everything App," has a succinct topline explanation: "The new OG Xbox Backwards Compatibility layer released by Microsoft for the PC is actually an Xbox 360 emulator running XeFu (the OG Xbox emu for the 360)," he wrote, pointing to telltale indicators visible in a dump of XeFu (the Xeon Fusion Emulator) pulled from the Fuzion Frenzy PC re-release.

For an even more in-depth explanation, developer Milenko has an article on the subject, also on X. The big takeaway? It's a "Beautiful piece of engineering. Also: Emulators, all the way down."

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Rewind all the way back to 2005: The very first instance of Xbox backwards compatibility on the 360 was XeFu emulation, as outlined in this 2018 video from Modern Vintage Gamer. When you popped your old Halo 2 or KotOR disk into a 360 back in the day, they weren't running natively on the console. The 360 emulated the original Xbox to run those games.

This tech is the basis of Microsoft's later backwards compatibility efforts on Xbox Series consoles as well. So instead of building a new Xbox emulator from scratch to run these games on PC, the company ported its in-house Xbox 360 emulator to PC, then ran XeFu through that. Pretty neat.

Meanwhile, the devs of the XWine1 project, an Xbox One translation layer for PC, shared that it's possible to use the in-development XWine1 with the dumped official emulator to get other OG Xbox and 360 games running on PC, though with "varying degrees of success."

As for how this will affect game preservation and end-user emulation quality in the long term, that remains to be seen. The xemu OG Xbox and Xenia 360 emulators have been in development and available for use for some time, but better public understanding of Microsoft's internal emulation methods can only be a good thing.

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