The Xbox One GPU: GCN-Based
While Microsoft and Sony both leverage AMD's Graphics Core Next architecture for their next-generation consoles, Microsoft's shader count is matched pretty well to the same Bonaire GPU found on the desktop Radeon HD 7790. Sony, on the other hand, appears to have a derivative of AMD's Pitcairn design found on the Radeon HD 7800s. Much has already been said comparing both devices and their capabilities. However, the fact that developers are running certain games at lower native resolutions on the Xbox One than the PS4 and then upscaling the output makes it pretty clear that Sony's GPU is more powerful.
But gaming consoles do not mirror the PC graphics card market. The fastest console doesn't always win, as Sega can attest to.
There are also some very significant differences between actual desktop GPUs and the hardware inside the Xbox One. For instance, Bonaire has 14 Compute Units. As we know, each CU has four Vector Units, and each VU contains 16 shaders. That adds up to 896 of AMD's Stream processors running at 1 GHz, in the case of Radeon HD 7790. We also know from digging deeper into the PS4 that Sony wanted eight of AMD's asynchronous compute engines in its GPU. AMD's mainstream GPUs have two. Clearly, they call these semi-custom designs for a reason.
The Xbox One's GPU sports 12 CUs, totaling 768 Stream processors, and a clock rate recently revised up to 853 MHz. Microsoft has also stated publicly that some of the GPU's resources will be reserved for the Kinect and operating environment, before we even get to differences in each console's memory bandwidth.
Microsoft equips the Xbox One's SoC with 8 GB of conventional DDR3-2133 memory in a quartet of channels. A 256-bit aggregate interface yields 68.3 GB/s of throughput, which is quite a ways behind the PS4’s 176 GB/s. But Microsoft has a trick up its sleeve. Taking a page from the Xbox 360 playbook, Microsoft embeds 32 MB in four 8 MB slices on 256-bit buses. At minimum, it's rated for 109 GB/s, though Microsoft also specifies a 204 GB/s peak.
Despite its comparatively less powerful GPU, AMD managed to build a very technically impressive SoC for the Xbox One. It measures a substantial 362mm2, which is pretty close to the Tahiti GPU on AMD's Radeon R9 280X measuring 352 mm2...and that's just a graphics processor. Yet, both are designed for next-gen gaming.