Original Xbox games on PC use Microsoft’s old Xbox 360 XeFu system

Microsoft introduced Xbox Backward Compatibility on PC this week, starting with Blinx: The Time Sweeper, Conker: Live & Reloaded, Crimson Skies and Fuzion Frenzy. The games are available through the Xbox app and support up to 4x resolution scaling, VSync and additional graphics settings.

Developer Nathan, also known as TheLunarixus, has now inspected files from the PC release of Fuzion Frenzy. According to his findings, the package contains XEX2 and STFS markers associated with Xbox 360 software. It also includes kernel strings such as “XENON KERNEL EXITING.”

How the two-stage emulation works

The original Xbox from 2001 used an x86 processor. Microsoft then switched to an IBM PowerPC processor for the Xbox 360, making the two consoles technically different despite sharing the Xbox name.

Microsoft created an emulator called Xenon Fusion, shortened to XeFu, to run original Xbox games on the Xbox 360. Michael Brundage, an engineer who worked on the project, confirms that the emulator executable was named xefu.xex.

The Windows implementation reportedly runs an Xbox 360 environment first. That environment loads XeFu, which then runs the original Xbox game. In basic terms, the PC emulates the Xbox 360 software needed to operate Microsoft’s existing original Xbox emulator.

This means the original x86 game is handled by software designed for the PowerPC-based Xbox 360, which is itself running on a modern x86 PC. Despite the additional stage, Microsoft lists a GeForce GTX 950, Radeon RX 550 or Intel Arc A310 as the minimum GPU. The minimum CPU requirement is a Core i3-10300 or Ryzen 3 3100.

What about Xbox 360 games?

The discovery suggests Microsoft already has an Xbox 360 execution environment working on Windows. In theory, Xbox 360 games could use this environment directly without loading XeFu, since XeFu is only required for original Xbox software.

However, this does not confirm that Xbox 360 games are coming to PC. The current files only show Xbox 360 components being used to run original Xbox games. Microsoft has said that more classic games will arrive over time, but it has not announced PC support for the Xbox 360 library.

Meanwhile, Kirby0Louise dug into the files a little deeper and discovered that there are several references to original Xbox games.

Microsoft may win twice here, giving gamers a chance to revisit some of the most iconic games from the OG Xbox/360 era, and charging some gamers to buy them again. Worth adding that the company has not yet confirmed plans for the rumored disc-to-digital conversion project.

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