[jayrox]

this is incorrect. according to microsoft they are running emulation.

Behind the scenes, Microsoft has built a full Xbox 360 emulator for its Xbox One console. "Xbox One Backward Compatibility is an Xbox 360 emulator that runs on Xbox One and is used to play Xbox 360 games," says a Microsoft spokesperson in a statement to The Verge.

http://www.theverge.com/2015/6/15/8785955/microsoft-xbox-one...

the package they are sending when you insert the disc is a container that contains the xbox emulator, any media assets, the game and compatibility stuff that is needed.

[nitrogen]

You keep quoting that same Verge quote of a spokesman. Do you have a more technical or independent source? Spokespeople are rarely accurate on a technical level.

[izacus]

Do you have any source that they're actually recompiling everything?

For example running original Xbox games on Xbox 360 also required a download of a binary which was an emulation / compatibility wrapper around the binary on the DVD that shimmed out and hotpatched code so the games worked properly.

[nitrogen]

The download sizes reported by other commenters seem to suggest a bit more than simple shims.

[chc]

The download sizes do suggest you're downloading a whole game, or at least most of one. This does not, however, imply that the game is ported -- just that they pull the game from the server rather than the disc. This makes sense even if they're emulating, because most Xbox 360 games will have received a lot of updates compared to what's on the disc, and Microsoft have probably only tested the emulation against one specific version.

[jayrox]

its also certainly possible that part of the emulation requirements include xbox 360 patch levels, an emulated file system for updates and everything else to be together in a single container.