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Microsoft sheds more light on the Xbox Velocity Architecture and its SFS component

Following the surprise reveal at The Game Awards last year, Microsoft has been pretty open about its next-gen console, providing a full spec sheet, details about the controller, the DirectX 12 Ultimate collection of APIs coming to Series X and PC, and what Series X optimized games can deliver. The firm also did a feature spotlight on Smart Delivery, which was a big focus of its May Inside Xbox episode. Now, it's the turn of the Xbox Velocity Architecture to be in the spotlight.

In a new post on Xbox Wire, penned by Director of Program Management at Xbox, Jason Ronald, the firm shared a bit more about its solution to the ever-increasing need to optimize asset streaming and access in games, a solution it calls Xbox Velocity Architecture. You can see a top level view of this in the trailer at the top of the post.

Essentially, Xbox Velocity Architecture (XVA) is really an umbrella term, and consists of four components: the custom NVMe SSD, hardware accelerated decompression, the DirectStorage API - present in DirectX 12 Ultimate -, and finally, Sampler Feedback Streaming or SFS.

Starting with the custom 1TB NVMe SSD, Microsoft states that this particular component delivers "40x the throughput of Xbox One" at its 2.4GB/s raw I/O throughput, figures that were shared previously. What wasn't shared previously is that the SSD is designed, much like the CPU and GPU, for "consistent, sustained performance", something that's also true of the Seagate Expandable Storage Cards that will be available to buy separately.

Moving on to hardware accelerated decompression, the Series X supports both the industry-standard general-purpose LZ decompressor, as well as Microsoft's proprietary, texture data-optimized BCPack solution, which can be used in parallel and thus reduce the overall size of the game package. Ronald also goes on to say:

Assuming a 2:1 compression ratio, Xbox Series X delivers an effective 4.8 GB/s in I/O performance to the title, approximately 100x the I/O performance in current generation consoles.

He further goes on to say that achieving this type of decompression performance via software alone would take up more than four Zen 2 CPU cores. It's important to mention that according to James Stanard - who is an engine architect and is involved in graphics optimization R&D at Microsoft -, the 4.8GB/s figure is "conservative", with ideal circumstances possibly leading to even better performance.

On the API front, the DirectStorage API was added to DirectX to enable devs to "establish multiple I/O queues", therefore reducing latency and "virtually eliminating load times or fast travel systems".

Last but not least, we come to Sampler Feedback Streaming. This gives devs more control over mipmaps, in other words, the array of game textures available for differing LODs (levels of detail). As you get closer to an object, you get a higher LOD, and without SFS, developers would have to "load an entire mip level in memory even in cases where they may only sample a very small portion of the overall texture", which is an inefficient use of available resources.

According to Jason Ronald, by adding specialized hardware to the Xbox One X, the team was able to see that the GPU frequently "accesses less than 1/3 of the texture data required to be loaded in memory", and as such, SFS was implemented on the Series X to mitigate this inefficiency. In summary:

This innovation results in approximately 2.5x the effective I/O throughput and memory usage above and beyond the raw hardware capabilities on average. SFS provides an effective multiplier on available system memory and I/O bandwidth, resulting in significantly more memory and I/O throughput available to make your game richer and more immersive.

As per Ronald, the Xbox Velocity Architecture makes it possible for the next-gen Xbox to deliver performance that's well beyond the listed hardware specs, with "instant, low level access to more than 100GB of game data stored on the SSD just in time for when the game requires it."

The tech behind this is no doubt impressive, and it's likely we'll see what it can do later this month, when Microsoft is set to show off a number of first-party games - among which 343 Industries' Halo Infinite - during the Xbox Games Showcase set for July 23.

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