One of the most memorable of E3 reveals also happens to be one of the greatest technological achievements of the current-gen era. Two-and-a-half years ago, Phil Spencer took to the stage at Los Angeles’ Galen Centre to showcase the original Xbox 360 version of Mass Effect running on Xbox One hardware. Following an impressive early access period, the backwards compatibility program rolled out in full force, and hundreds of Xbox 360 titles are now available to play on Xbox One, with a clutch of enhanced 4K games now available for Xbox One X. So how was this all achieved? How does back-compat actually work?
Across the years, we’ve only picked up a few titbits on the process – essentially that the original Xbox 360 PowerPC executables are reverse-engineered into an intermediate, then recompiled into x86. There’s also been talk of some level of hardware compatibility integrated into the Xbox One processor to make the job easier, but beyond that, technical details on the process are thin on the ground – until now.
“Basically, we have a VGPU – or an Xbox 360 GPU that we’ve recompiled into x86 – and we run the entire 360 OS stack,” explains Bill Stillwell, Xbox Platform Lead. “We take each game, we recompile it so that it runs, but basically we’re running it still in a 360, and the team goes through the game with multiple passes.”
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