Microsoft have told developers they have improved the performance of the internal 32mb ESRAM greatly in console that are launching, so even XB1 with its DDR3, might now be faster then PS4's GDDR5
This chart showing the PS4 peaking at 176gb/s compared to the early XB1 devkits running at 102gb/s is no longer true, as now Microsoft claims they been able to boost the speed of the ESRAM in production consoles (the ones you going to buy this holiday season) and the top speed in theory is now 192gb/s, making the XB1 now faster with its cheaper/slower DDR3 then the PS4 with its direct (no embedded cache to help it out) and more costly GDDR5 but normally faster.
Of course this is all peak theoretical throughput, it all depends on how good the developer is to be able to code their main graphics loops that need the high-bandwidth graphics speed like shadowmaps, lightmaps, depth targets and render targets to fit all with 32mb of space, Killzone developers claim they need 800mb of space, so 32mb is nothing, but still this boost in internal top theoretical speed can be usage if you know all the specs. and tricks of the system, so I can see exclusive games like Halo or Titanfall working with this to make their games look outstanding on the XB1 compared to the PS4, whereas multi-console games, the developer will most likely just default their engine to usage the slowest of the two systems, now being the PS4, instead of re-coding custom graphics elements that can improve the game's overall look just for the XB1 release.
Well-placed development sources have told Digital Foundry that the ESRAM embedded memory within the Xbox One processor is considerably more capable than Microsoft envisaged during pre-production of the console, with data throughput levels up to 88 per cent higher in the final hardware.
Bandwidth is at a premium in the Xbox One owing to the slower DDR3 memory employed in the console, which does not compare favourably to the 8GB unified pool of GDDR5 in the PlayStation 4. The 32MB of "embedded static RAM" within the Xbox One processor aims to make up the difference, and was previously thought to sustain a peak theoretical throughput of 102GB/s - useful, but still some way behind the 176GB/s found in PlayStation 4's RAM set-up. Now that close-to-final silicon is available, Microsoft has revised its own figures upwards significantly, telling developers that 192GB/s is now theoretically possible.
So how could Microsoft's own internal tech teams have underestimated the capabilities of its own hardware by such a wide margin? Well, according to sources who have been briefed by Microsoft, the original bandwidth claim derives from a pretty basic calculation - 128 bytes per block multiplied by the GPU speed of 800MHz offers up the previous max throughput of 102.4GB/s. It's believed that this calculation remains true for separate read/write operations from and to the ESRAM. However, with near-final production silicon, Microsoft techs have found that the hardware is capable of reading and writing simultaneously. Apparently, there are spare processing cycle "holes" that can be utilised for additional operations. Theoretical peak performance is one thing, but in real-life scenarios it's believed that 133GB/s throughput has been achieved with alpha transparency blending operations (FP16 x4).
The news doesn't quite square with previous rumours suggesting that fabrication issues with the ESRAM component of the Xbox One processor had actually resulted in a downclock for the GPU, reducing its overall capabilities and widening the gulf between graphical components of the Xbox One and the PlayStation 4. While none of our sources are privy to any production woes Microsoft may or may not be experiencing with its processor, they are making actual Xbox One titles and have not been informed of any hit to performance brought on by production challenges. To the best of their knowledge, 800MHz remains the clock speed of the graphics component of the processor, and the main CPU is operating at the target 1.6GHz. In both respects, this represents parity with the PlayStation 4.
Of course again this late sudden change in retail production versions over earlier devkits, will most likely be too late to improve 'launch games', but developers working on titles releasing in 2014 like Titanfall, will now have time to get newer devkits from Microsoft, and fine-tune their engines to make full usage of the very fast ESRAM speeds, so as the next year rolls along we will more able to visually see which system is better, welcome to round 2 of XB1 vs. PS4, the next-gen battle for top graphics is on!
NEWS SOURCE #1: Xbox One memory better in production hardware (via) EuroGamer
NEWS SOURCE #2: Xbox One memory performance improved for production console (via) 360Crunch