Little is actually known about the Xbox 720, but many rumors are currently floating around about the hardware it's set to contain.
By sifting through dozens of Microsoft job listings, OXM.co.uk's Edwin Evans-Thirlwell managed to discover actual evidence for the next-generation Xbox and the hardware it'll carry. According to his discoveries, we now know that the Xbox 720 will use the x86 processing architecture, which is what the PC and the Xbox 720's counterpart at Sony, the PlayStation 4, uses. It's a huge change from the Xbox 360's PowerPC setup.
What this means is that the Xbox 720 is unlikely to offer any sort of backwards compatibility for existing Xbox 360 games due to the drastic change in processing architecture. It's possible that Microsoft will allow gamers to stream Xbox 360 games directly from the Xbox servers, but that's the extent of it.
In addition to the discoveries made by OXM.co.uk, Videogamer.com has discovered that a number of multiple current and former Microsoft employees have disclosed the details about their work on the next-gen platform through their online CVs.
In newly updated LinkedIn profiles, Microsoft employees Rishi Jain, a system validation engineer; Parag Garg, a former program manager; Avi Bar-Zeev, former principal architect; and Maxwell Churchill, Microsoft's ex-visual designer, each list their work on the next-gen Xbox, which they refer to as the "Xbox 2013" or "next-gen Xbox".
Given these multiple developments, it's safe to assume that Microsoft will be making an announcement about the Xbox 720 sometime before E3.