Xbox One APU doesn’t measure up to PS4: analysis

Following the dissection of the AMD APU inside of the Playstation 4 by Chipworks, the company turned its attention to Microsoft’s Xbox One and stripped the chip down to its bare elements to photograph it.

In comparison to the Playstation 4, the Xbox One’s APU measures up at 363mm², while the PS4’s APU comes in at 348mm². The dies are pretty big. For comparison, the Core i7-4770K measures in at 177mm², AMD’s A10-6800K has a die size of 246mm², and the Radeon HD7870 sits at 212mm².

The die shots confirm that Microsoft practices a similar method of fault tolerance to Sony’s custom APU design. The Xbox One APU contains fourteen GPU shader modules, but disables two of them to improve chip yields and not throw away units that don’t have all fourteen shader modules functional.

The APU also has three SRAM caches – two sets of 16MB SRAM caches accessed by the GPU and a smaller set of SRAM that is used for Microsoft’s customised SHAPE sound processor, which shares some elements of AMD’s TrueAudio technology. SHAPE has its own processing hardware and giving it some SRAM of its own means it won’t be bottlenecked by bandwidth constraints.

Xbox One APU photographed by Chipworks

Looking at the chip itself, Microsoft chose to dedicate a large portion of the available die area to the SRAM used almost exclusively by the GPU. Microsoft’s plan for the One is far-reaching and concentrates on the console being an all-round performer rather than a dedicated games console with media features being secondary.

But the SRAM choice results in the chip being much larger than the APU found in the Playstation 4 ($110 to $100 respectively) and the more complex layout requires die yields to be near perfect in order to get enough chips that work to make manufacturing a single wafer worth the cost.

Microsoft disables two shader modules to allow for this, but this isn’t the case with faulty SRAM – if even one 1MB block is faulty or not up to specification, that chip needs to be thrown away.

Its also probable that Microsoft will see less of a price drop as manufacturing for the APUs become cheaper – a large portion of the budget goes to the SRAM modules and not only are they tricky to make, they’re also very expensive. As volume ramps up for Sony, on the other hand, their console could see price drops much sooner in its lifetime.

This is a change from how Microsoft set up the Xbox 360. On the older console, the eDRAM, which weighed in at 10MB, was a separate chip soldered onto the motherboard. Because it was made separately, yields were much better and Microsoft did not need to factor it into their manufacturing of the 360’s CPU and GPU.

As far as similarities between the chips go, both APUs have a 256-bit memory bus shared between all processing units, both have two quad-core AMD Jaguar processors built on the Steamroller architecture, and both have stock-standard Graphics Core Next shaders arranged in 64 shaders per module.

Xbox One and Playstation 4 APU side-by-side comparison

With the Xbox One only having accessible twelve shader modules and the PS4 boasting eighteen, how will Microsoft overcome the performance gulf that exists not only in graphics horsepower, but also in memory bandwidth? The company says that it will offload certain tasks into the Xbox Live cloud to free up system resources, and over time more parts of games that don’t have to be calculated in real time will be moved into the cloud.

One title that already utilises such a feature is Forza Motorsport 5, which takes the ghost car lap times that other players create (called a Drivatar) and uses that data to train the game’s AI, which is hosted on cloud servers for Xbox One consoles that are connected to the internet.

In the future, Microsoft also promises the ability to use pre-baked lighting models in complex game environments. The models will be sent to the console through the internet, which is something that could have benefited Ryse: Son of Rome. Ryse currently does all of its lighting simulations on the fly, which is one of the reasons why Crytek opted to drop to the 900p resolution and target a frame rate or around 30 fps.

However, that is only an option for future titles. For now, Sony’s extra graphical horsepower helps in reducing the performance hits that AI calculations and lighting models incur on the system and ensures that games played offline retain the same playability and user experience.

Source: Chipworks

More Xbox news:

SA Xbox Games with Gold December titles confirmed

Spend R17,000 on Forza 5 car DLC if you’re lazy

Xbox One error messages provide mirth, not much else

Vote with your money on micro-transaction DLC: Microsoft