Xbox One Family System Hardware Overview
Advanced Technology Group
Updated June 12th 2017
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Basic hardware specifications
The Xbox One console is powered by custom hardware design that includes an 8-core, 64-bit CPU running at 1.75 GHz, an 853 MHz GPU, and a number of custom hardware blocks. The Xbox One S GPU runs at 914 MHz. The Xbox One X CPU runs at 2.3 GHz and the GPU runs at 1.172 GHz. See the retail system block diagrams for details of the overall system architecture. Both Xbox One and Xbox One S retail consoles and development kit hardware have 8 GB of unified memory. The Xbox One X retail consoles have 12 GB of unified memory, and the Xbox One X Development Kit has 24 GB of unified memory. There is no requirement for graphics resources to be located in dedicated video RAM.
CPU
The Xbox One family of consoles includes a CPU with a total of eight processor cores, where each core has one fully independent hardware thread with no shared execution resources. Each core is an advanced x64 processor running at 1.75 GHz (2.3 GHz on Xbox One X). The eight independent processor cores are organized into two modules of four cores each. The Xbox One CPU architecture includes state-of-the-art features such as out-of-order processing with speculative execution, store forwarding, register renaming, and advanced branch-prediction hardware. These features enable the CPU to hide a significant number of potential pipeline stalls.
Each hardware thread can retire two instructions per clock tick. At peak performance, the Xbox One CPUs can retire up to 28.0 billion instructions per second. Xbox One X, due to its higher clock rate, can retire up to 36.8 billion instructions per second. As a result of out-of-order execution and many other architectural improvements, the Xbox One CPU is expected to consistently achieve an IPC value in the range of 0.6 to 1.0, assuming optimal cache usage by the title.
System block diagrams
These diagrams illustrate overall system architecture for Xbox One, Xbox One S, and Xbox One X consoles.
Xbox One and Xbox One S system block diagram
Xbox One X system block diagram
As a state-of-the-art x64 processor, the CPU supports the standard x64 instruction-set architecture, including streaming SIMD extension (SSE) varieties up to and including SSE 4.2, and support for cryptographic instructions. The CPU also supports the AVX instruction set, including 256-bit wide SSE registers (YMM0-15) and three operand instructions providing non-destructive register syntax. The CPU decodes AVX instructions into two 128-bit wide SIMD micro-operations during instruction decode.
CPU caches
Each CPU core has its own 32 KB L1 instruction cache and 32 KB L1 data cache. Each module of four CPU cores has a 2 MB L2 cache, resulting in a total of 4 MB of L2 cache. The L2 cache is the first sharing point between CPU cores.
The CPU supports explicit cache prefetch instructions. However, both the L1 and L2 caches include special hardware for intelligent prefetching of data. The hardware prefetch units monitor data-access patterns and predict future data requests. The prefetch units predict both sequential and strided data access with positive or negative offsets. As a result, data will often be resident in the cache before the CPU explicitly requests it. The L2 cache system provides a slightly lower penalty for a remote L2 cache hit relative to a main memory fetch.
GPU
Xbox One and Xbox One S share the same GPU architecture, with the Xbox One S GPU clock running at a slightly higher rate. The Xbox One X GPU has an even higher clock rate and contains over three times more compute units, and double the amount of dedicated vertex and pixel hardware.
| Xbox One | Xbox One S | Xbox One X | |
|---|---|---|---|
| Compute Units | 12 | 12 | 40 |
| IA (Input Assembler) | 1 | 1 | 2 |
| VGT (Vertex Grouper) | 2 | 2 | 4 |
| RB (Render Backend) | 4 | 4 | 8 |
| DB (Depth Block) | 4 | 4 | 8 |
The increase in clock rate and extra components allow much higher peak rates on Xbox One X.
| Xbox One | Xbox One S | Xbox One X | |
|---|---|---|---|
| Clock Speed | 853MHz | 914MHz | 1.172GHz |
| Peak FLOPS | 1.3 TFLOPS | 1.4 TFLOPS | 6 TFLOPS |
| Pixel/sec | 13.6 Gpix | 14.5 Gpix | 37.5 Gpix |
| Vertex/sec | 1.7 Gvert | 1.8 Gvert | 4.7 Gvert |
| Triangle/sec | 1.7 Gtri | 1.8 Gtri | 4.7 Gtri |
| Texture Fetch/sec | 41 Gtex | 43.9 Gtex | 188 Gtex |
The Xbox One graphics architecture has a unique design implementing a superset of Direct3D 12. The GPU operates on virtual addresses for resources using its own 64-bit memory management unit (MMU). The graphics architecture incorporates a number of important features and extensions, including GPU-specific L1 and L2 caches, hardware virtualized texture memory, compression for color and depth buffers with or without MSAA, atomic operations, reads and writes coherent with the CPU caches, the ability to explicitly flush its own cache lines, and three fully independent display planes.
The Xbox One X GPU also supports additional features such as out-of-order rasterization and DCC compression.
Display planes, HDR, and 4K Rendering
Titles have access to two of the display planes. The system reserves the third display plane for system UI and notifications. Each display plane can have arbitrary position, resolution, format, refresh rate, and size relative to the screen. The display planes can be scaled independently in hardware to the final display output resolution. On Xbox One, the display planes are composited using source alpha, and alpha values can also be pre-multiplied. This is also supported on Xbox One S provided that HDR rendering is not being used. When HDR rendering is being used on Xbox One S, and at all times on Xbox One X, display-plane compositing is not supported. In this case, one plane is used for SDR and the other is used for HDR rendering.
Additionally, Xbox One S and Xbox One X can support a single 3840x2160 swap chain with these formats.
| Hardware | Scenario |
|---|---|
| Xbox One | 4K output is not supported |
| Xbox One S | 4K non-HDR output supported on single display plane |
| Xbox One X | 4K HDR output on single display plane |
Memory and bandwidth
Both the Xbox One retail console and development kits have 8 GB of DDR3 system memory. The peak system memory read/write bandwidth is 68 GB/sec. Xbox One X has significant changes in memory: 12 GB of GDDR5 memory and a peak bandwidth of 326 GB/sec. The entire family has the same unified memory architecture, which means that system memory is equally accessible to both the CPU and the GPU. Xbox One and Xbox One S consoles have 32 MB of fast embedded SRAM (ESRAM) with a peak bandwidth of 109 GB/sec. The GPU can directly access resources that reside in either system memory or ESRAM. Embedded RAM can therefore be used as flexible, high-speed scratch memory that can be both read from and written to by the GPU. From the GPU’s perspective, the bandwidths of system memory and ESRAM are parallel, providing combined peak bandwidth of 177 GB/sec.
Because the GPU operates on virtual addresses, there are no functional differences between ESRAM and system memory. Titles are free to choose where various GPU-accessible resources reside, including the frame and depth or stencil buffers. The only exception is the front buffer, which must reside in system memory. A unique benefit of this architecture is that it’s possible, by means of page-table mappings, for a frame buffer to be constructed that includes page-sized mixtures of both ESRAM and system memory.
Xbox One X contains several changes to the memory system. The DDR3 memory on Xbox One and Xbox One S has been replaced with GDDR5 memory. The 32 MB of ESRAM has been removed. The change to GDDR5 memory results in drastically higher memory performance and alleviates the need for ESRAM.
The following table compares the specifications for the memory architecture of the consoles.
| Xbox One | Xbox One S | Xbox One X | |
|---|---|---|---|
| Memory clock speed | 2133MHz | 2133MHz | 6800MHz |
| Bus width | 256 bit | 256 bit | 384 bit |
| Total DRAM | 8GB | 8GB | 12GB |
| ERA DRAM size | 5GB | 5GB | 9GB |
| Bytes/sec DRAM | 68 GB/sec | 68 GB/sec | 326 GB/sec |
| Bytes/sec ESRAM | 109 GB/sec | 117 GB/sec | N/A |
| HDD sustained read | 40 MB/sec | 40 MB/sec | 60 MB/sec |
Move Engines
The Xbox One family GPU contains dedicated hardware units called Move Engines for block memory transfer operations. There are four Move Engines in total. They perform copy operations to and from any combination of system memory or ESRAM. Each of the Move Engines can optionally apply texture swizzle or un-swizzle transformations to data as it is transferred. One of the Move Engines can perform an LZ77 encode, while another can perform either an LZ77 or JPEG decode.
Video codec
The Xbox One family includes dedicated hardware that can perform video encode and decode operations. The video codec hardware in Xbox One and Xbox One S supports 1080p encode and decode at 30 Hz. Titles can decode VC1, MPEG2, and H.264 using High profile. Titles can encode H.264 video using Baseline profile level 4.2. The video codec hardware in Xbox One X has been upgraded and supports 4K video at 60Hz.
Storage
All Xbox One family retail consoles include a hard disk drive (HDD) and an optical disc drive (ODD). The Xbox One family also includes embedded flash memory, which is reserved for system use to accelerate certain system operations.
Titles have access to data stored on the hard disk drive and to data stored remotely in the cloud by way of Xbox Live services. The Xbox One and Xbox One S hard disk can deliver sustained read speeds of up to 40 MB/sec over any two-second window. Xbox One X has a faster hard disk that can deliver sustained read speeds of up to 60 MB/sec over any two-second window. The system will reserve a portion of the HDD for its own use.
The Xbox One optical disc drive is a high-capacity drive providing up to 50 GB of physical storage. The ODD provides an average of 18 MB/sec throughput, with an anticipated 200 ms seek time including layer switch. Titles cannot directly access data on the ODD. Instead the ODD is used by the system for installation of full titles to the hard disk drive. Titles provide a file manifest defining the minimal files required to begin execution in priority order. This system enables the title to begin executing while file installation continues in the background.
Input/Output
Xbox One consoles are designed for high-bandwidth connectivity. The console has built-in Wi-Fi networking and a wired Gigabit Ethernet port. Attached devices, including Kinect, connect to USB 3.0 ports. Controllers connected to Xbox One are wireless only; there are no dedicated controller ports. Controllers can be attached to the USB ports, but this is only for battery charging and initial wireless synchronization. Video output is provided by High Definition Multimedia Interface (HDMI) 1.4a, which enables full 1080p stereo display output. Xbox One X has an upgraded HDMI interface: it’s been changed to HDMI 2.0b and supports full 4K HDR display output. Audio output support is provided by either HDMI or Sony/Phillips Digital Interconnect Format (S/PDIF).
Audio
Audio in the Xbox One family of consoles is provided by several dedicated hardware components. These components include an audio signal processing block, an audio codec processor, a multi-channel echo cancellation (MEC) processor, and a scheduling processor. The console can output discrete, 7.1-channel, linear pulse-code modulation (PCM) data.
The Scalable Hardware Audio Processing Engine (SHAPE) block provides hardware XMA decoding for up to 512 voices, hardware mixing buffers, parametric equalization, filtering, and compressor/limiter dynamic range control. Typical XMA2 compression ratios range from 6:1 to 14:1. The SHAPE block can store and process 512 audio frame instances of 128 samples at 48 KHz (2.67 ms). It can also use dedicated direct memory access (DMA) hardware to access data in system memory, allowing for intra-frame, CPU-based, and hardware-accelerated processing to be combined as the title demands.
The Audio Scalar Processor (ASP) is a codec block providing voice chat and audio codecs such as xWMA. Typical xWMA compression ratios range from 20:1 to 40:1.
The Audio Vector Processor (AVP) performs multi-channel echo cancellation (MEC) on the incoming Kinect audio stream for speech recognition and chat.
Kinect
The Kinect sensor for Xbox One represents a significant advancement in natural user input (NUI) technology. Unique, new, and improved features of the Xbox One Kinect sensor include: a wider field of view, a lighting-independent active IR stream, an improved depth sensor with increased resolution, accuracy, and precision, and an HD RGB sensor. Xbox One provides a dedicated USB 3.0 bus for Kinect by using a custom plug. However, the dedicated Kinect port has been removed from Xbox One S and Xbox One X. The user connects the Kinect through one of the existing USB ports.
The wider field of view means that a tilt motor is no longer required for Kinect to work effectively in various environments. A person who is six feet tall can stand two feet closer to the sensor with the same tracking fidelity.
The active IR stream provides a lighting-independent IR image at 30 Hz. The IR stream provides a grayscale image that is independent of ambient lighting, enabling more robust image processing. High-quality, low-noise depth data results in improved skeletal tracking and player identification.
The Kinect sensor also includes an RGB color sensor with 1080p resolution. The RGB sensor has a full-frame shutter that captures video at up to 30 Hz.
The Kinect sensor also incorporates an array microphone with multi-channel echo cancellation (MEC) that has full hardware acceleration.
Xbox One development kits
Xbox One title development occurs on a PC running 64-bit Windows 7 Service Pack 1, Windows 8.1, or Windows 10. The resulting executable image is deployed by development kit software and remotely debugged on the development computer.
The Xbox One X development kit contains several additions over the retail console:
- An additional 12GB of memory, for a total of 20GB available to the title.
- 4 additional compute units on the GPU, for a total of 44 compute units.
The development kit can represent an Xbox One or Xbox One S, although this representation is not 100% accurate. We recommend that you use the following matrix for testing.
| Daily Iteration | Final Optimization | |
|---|---|---|
| Xbox One | Xbox One X Dev Kit | Xbox One Dev Kit |
| Xbox One S | Xbox One X Dev Kit | Xbox One S Dev Kit |
| Xbox One X | Xbox One X Dev Kit | Xbox One X Dev Kit |
Visual Studio 2015 and Visual Studio 2017 provide the host development environment. The Xbox One compiler is the native compiler provided by Visual Studio. Because of this, all features of the C++ standard that are supported by Visual Studio are available for Xbox One development.
Summary
The Xbox One family of consoles is balanced and fine-tuned to provide powerful hardware that developers can effectively leverage by using familiar tools such as Visual C++ and PIX. The hardware architecture differences between the various consoles are slight. Overall these are only increases in performance through changes in clock speed, available GPU resources, and additional memory.