There is nothing strange about it. The original Xbox used a custom NVidia chipset for GPU, sound, peripherals, network etc. The only semi off-the-shelf part was the Intel&#x27;s CPU (the exact same CPU was not on the market but it seems like a different packaging of a regular Celeron). The system is very complex and all its documentation is very confidential, it was not given to the third parties and, by this time, I am afraid even NVidia does not have it readily available so you cannot hope somebody will break the NDA and release it. The same is true for the later generations: 360, PS3, PS4, X1 all have custom chipsets and SoC in the current gen. Having a known ISA from the point of view of writing an emulator is similar to having a known encoding when writing a translation program from an unknown language.