http://www.joystiq.com/2013/04/08/bl...-x86-amd-chip/

Microsoft will match Sony's example and use an X86 series processor from AMD in its next console, according toBloomberg's anonymous sources. The still-unannounced console is said to use a "Jaguar" CPU with integrated GPU, abandoning the IBM PowerPC tech used in the Xbox 360.
That means, like the PS4, the new Xbox will have difficulty emulating its predecessor, since it will be built on different architecture. The good news, however, is that with both of those consoles (allegedly) using similar architecture, and PCs also similarly laid out, multiplatform game development will be much easier.