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The secret sauce | Xbox Velocity Architecture



Microsoft is determined to not repeat their missteps of the past with their next-gen super console, Xbox Series X. Microsoft says in a blog post, that they set out to create a console with “no compromises,” that would ensure that “no component would constrain the creative ambition of the world’s best creators, empowering them to deliver truly transformative next gen gaming experiences not possible in prior console generations.”

The beating heart of Xbox Series X is AMD’s latest “RDNA 2 and Zen 2 Architectures,” that generates 12 Teraflops of GPU power and 4 times the CPU power of Xbox One X. Microsoft goes on to detail the rest of the specs, “Xbox Series X includes the highest memory bandwidth of any next generation console with 16GB of GDDR6 memory, including 10GB of GPU optimized memory at 560 GB/s to keep the processor fed with no bottlenecks.”

Storage needed to be radically rethought and revolutionized

Microsoft details how when they started to analyze the storage subsystem, “it became clear that we had reached the upper limits of traditional hard drive technology and to deliver on our design aspirations.” Feedback the Xbox team received back from game developers over the last few years was that “level designers are still often required to create narrow pathways, hallways, or elevators to work around the limitations of a traditional hard drive and I/O pipeline.”

Raise your hand if you are the average gamer and didn’t know that. The company goes on to explain how the constrained hardware influenced level development and often constrained “the ambition for truly transformative games.”

Xbox Velocity Architecture

The Velocity Architecture (XVA), according to Microsoft was “designed as the ultimate solution for game asset streaming in the next generation.”

If our custom designed processor is at the heart of the Xbox Series X, the Xbox Velocity Architecture is the soul.

Because the I/O subsystem was completely “rethought,” the new approach “directly directly influenced all aspects of the Xbox Series X design.” Microsoft then described the ” custom designed processor is at the heart of the Xbox Series X, the Xbox Velocity Architecture is the soul.”

The four major components of XVA

Microsoft then went on to describe the four components of XVA, Microsoft’s custom NVME SSD, hardware accelerated decompression blocks, a new DirectStorage API layer and finally their Sampler Feedback Streaming (SFS):

  • Custom NVME SSD: The foundation of the Xbox Velocity Architecture is our custom, 1TB NVME SSD, delivering 2.4 GB/s of raw I/O throughput, more than 40x the throughput of Xbox One. Traditional SSDs used in PCs often reduce performance as thermals increase or while performing drive maintenance. The custom NVME SSD in Xbox Series X is designed for consistent, sustained performance as opposed to peak performance. Developers have a guaranteed level of I/O performance at all times and they can reliably design and optimize their games removing the barriers and constraints they have to work around today. This same level of consistent, sustained performance also applies to the Seagate Expandable Storage Card ensuring you have the exact same gameplay experience regardless of where the game resides.
  • Hardware Accelerated Decompression: Game packages and assets are compressed to minimize download times and the amount of storage required for each individual game. With hardware accelerated support for both the industry standard LZ decompressor as well as a brand new, proprietary algorithm specifically designed for texture data named BCPack, Xbox Series X provides the best of both worlds for developers to achieve massive savings with no loss in quality or performance. As texture data comprises a significant portion of the total overall size of a game, having a purpose built algorithm optimized for texture data in addition to the general purpose LZ decompressor, both can be used in parallel to reduce the overall size of a game package. 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. To deliver similar levels of decompression performance in software would require more than 4 Zen 2 CPU cores.
  • New DirectStorage API: Standard File I/O APIs were developed more than 30 years ago and are virtually unchanged while storage technology has made significant advancements since then. As we analyzed game data access patterns as well as the latest hardware advancements with SSD technology, we knew we needed to advance the state of the art to put more control in the hands of developers. We added a brand new DirectStorage API to the DirectX family, providing developers with fine grain control of their I/O operations empowering them to establish multiple I/O queues, prioritization and minimizing I/O latency. These direct, low level access APIs ensure developers will be able to take full advantage of the raw I/O performance afforded by the hardware, resulting in virtually eliminating load times or fast travel systems that are just that . . . fast.
  • Sampler Feedback Streaming (SFS): Sampler Feedback Streaming is a brand-new innovation built on top of all the other advancements of the Xbox Velocity Architecture. Game textures are optimized at differing levels of detail and resolution, called mipmaps, and can be used during rendering based on how close or far away an object is from the player. As an object moves closer to the player, the resolution of the texture must increase to provide the crisp detail and visuals that gamers expect. However, these larger mipmaps require a significant amount of memory compared to the lower resolution mips that can be used if the object is further away in the scene. Today, developers must load an entire mip level in memory even in cases where they may only sample a very small portion of the overall texture. Through specialized hardware added to the Xbox One X, we were able to analyze texture memory usage by the GPU and we discovered that the GPU often accesses less than 1/3 of the texture data required to be loaded in memory. A single scene often includes thousands of different textures resulting in a significant loss in effective memory and I/O bandwidth utilization due to inefficient usage. With this insight, we were able to create and add new capabilities to the Xbox Series X GPU which enables it to only load the sub portions of a mip level into memory, on demand, just in time for when the GPU requires the data. 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.


All of this combined gives Xbox Series X, “significant increases in efficiency provided by Sampler Feedback Streaming, the Xbox Velocity Architecture enables the Xbox Series X to deliver effective performance well beyond the raw hardware specs, providing direct, instant, low level access to more than 100GB of game data stored on the SSD just in time for when the game requires it. These innovations will unlock new gameplay experiences and a level of depth and immersion unlike anything you have previously experienced in gaming.”

Are you buying Xbox Series X this year? Let us know in the comments below.



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