X
Xenon
(from what I've read, much of the following info on Xenon aka Xbox2 is
accurate, though some changes will have occured by the time the final
machine ships)
Xenon Hardware Overview
By Pete Isensee, Development Lead, Xbox Advanced Technology Group
This documentation is an early release of the final documentation, which may
be changed substantially prior to final commercial release, and is
confidential and proprietary information of MS Corporation. It is disclosed
pursuant to a nondisclosure agreement between the recipient and MS.
"Xenon" is the code name for the successor to the Xbox® game console from
MS. Xenon is expected to launch in 2005. This white paper is designed to
provide a brief overview of the primary hardware features of the console
from a game developer's standpoint.
Caveats
In some cases, sizes, speeds, and other details of the Xenon console have
not been finalized. Values not yet finalized are identified with a "+" sign,
indicating that the numbers may be larger than indicated here. At the time
of this writing, the final console is many months from entering production.
Based on our experience with Xbox, it's likely that some of this information
will change slightly for the final console.
For additional information on various hardware components, see the other
relevant white papers.
Hardware Goals
Xenon was designed with the following goals in mind:
..Focus on innovation in silicon, particularly features that game developers
need. Although all Xenon hardware components are technologically advanced,
the hardware engineering effort has concentrated on digital performance in
the CPU and GPU.
..Maximize general purpose processing performance rather than fixed-function
hardware. This focus on general purpose processing puts the power into the
Xenon software libraries and tools. Rather than being hamstrung by
particular hardware designs, software libraries can support the latest and
most efficient techniques.
..Eliminate the performance issues of the past. On Xbox, the primary
bottlenecks were memory and CPU bandwidth. Xenon does not have these
limitations.
Basic Hardware Specifications
Xenon is powered by a 3.5+ GHz IBM PowerPC processor and a 500+ MHz ATI
graphics processor. Xenon has 256+ MB of unified memory. Xenon runs a custom
operating system based on MS® Windows NT®, similar to the Xbox operating
system. The graphics interface is a superset of MS® Direct3D® version 9.0.
CPU
The Xenon CPU is a custom processor based on PowerPC technology. The CPU
includes three independent processors (cores) on a single die. Each core
runs at 3.5+ GHz. The Xenon CPU can issue two instructions per clock cycle
per core. At peak performance, Xenon can issue 21 billion instructions per
second.
The Xenon CPU was designed by IBM in close consultation with the Xbox team,
leading to a number of revolutionary additions, including a dot product
instruction for extremely fast vector math and custom security features
built directly into the silicon to prevent piracy and hacking.
Each core has two symmetric hardware threads (SMT), for a total of six
hardware threads available to games. Not only does the Xenon CPU include the
standard set of PowerPC integer and floating-point registers (one set per
hardware thread), the Xenon CPU also includes 128 vector (VMX) registers per
hardware thread. This astounding number of registers can drastically improve
the speed of common mathematical operations.
Each of the three cores includes a 32-KB L1 instruction cache and a 32-KB L1
data cache. The three cores share a 1-MB L2 cache. The L2 cache can be
locked down in segments to improve performance. The L2 cache also has the
very unusual feature of being directly readable from the GPU, which allows
the GPU to consume geometry and texture data from L2 and main memory
simultaneously.
Xenon CPU instructions are exposed to games through compiler intrinsics,
allowing developers to access the power of the chip using C language
notation.
GPU
The Xenon GPU is a custom 500+ MHz graphics processor from ATI. The shader
core has 48 Arithmetic Logic Units (ALUs) that can execute 64 simultaneous
threads on groups of 64 vertices or pixels. ALUs are automatically and
dynamically assigned to either pixel or vertex processing depending on load.
The ALUs can each perform one vector and one scalar operation per clock
cycle, for a total of 96 shader operations per clock cycle. Texture loads
can be done in parallel to ALU operations. At peak performance, the GPU can
issue 48 billion shader operations per second.
The GPU has a peak pixel fill rate of 4+ gigapixels/sec (16 gigasamples/sec
with 4× antialiasing). The peak vertex rate is 500+ million vertices/sec.
The peak triangle rate is 500+ million triangles/sec. The interesting point
about all of these values is that they're not just theoretical-they are
attainable with nontrivial shaders.
Xenon is designed for high-definition output. Included directly on the GPU
die is 10+ MB of fast embedded dynamic RAM (EDRAM). A 720p frame buffer fits
very nicely here. Larger frame buffers are also possible because of
hardware-accelerated partitioning and predicated rendering that has little
cost other than additional vertex processing. Along with the extremely fast
EDRAM, the GPU also includes hardware instructions for alpha blending,
z-test, and antialiasing.
The Xenon graphics architecture is a unique design that implements a
superset of Direct3D version 9.0. It includes a number of important
extensions, including additional compressed texture formats and a flexible
tessellation engine. Xenon not only supports high-level shading language
(HLSL) model 3.0 for vertex and pixel shaders but also includes advanced
shader features well beyond model 3.0. For instance, shaders use 32-bit IEEE
floating-point math throughout. Vertex shaders can fetch from textures, and
pixel shaders can fetch from vertex streams. Xenon shaders also have the
unique ability to directly access main memory, allowing techniques that have
never before been possible.
As with Xbox, Xenon will support precompiled push buffers ("command buffers"
in Xenon terminology), but to a much greater extent than the Xbox console
does. The Xbox team is exposing and documenting the command buffer format so
that games are able to harness the GPU much more effectively.
In addition to an extremely powerful GPU, Xenon also includes a very
high-quality resize filter. This filter allows consumers to choose whatever
output mode they desire. Xenon automatically scales the game's output buffer
to the consumer-chosen resolution.
Memory and Bandwidth
Xenon has 256+ MB of unified memory, equally accessible to both the GPU and
CPU. The main memory controller resides on the GPU (the same as in the Xbox
architecture). It has 22.4+ GB/sec aggregate bandwidth to RAM, distributed
between reads and writes. Aggregate means that the bandwidth may be used for
all reading or all writing or any combination of the two. Translated into
game performance, the GPU can consume a 512×512×32-bpp texture in only 47
microseconds.
The front side bus (FSB) bandwidth peak is 10.8 GB/sec for reads and 10.8
GB/sec for writes, over 20 times faster than for Xbox. Note that the 22.4+
GB/sec main memory bandwidth is shared between the CPU and GPU. If, for
example, the CPU is using 2 GB/sec for reading and 1 GB/sec for writing on
the FSB, the GPU has 19.4+ GB/sec available for accessing RAM.
Eight pixels (where each pixel is color plus z = 8 bytes) can be sent to the
EDRAM every GPU clock cycle, for an EDRAM write bandwidth of 32 GB/sec. Each
of these pixels can be expanded through multisampling to 4 samples, for up
to 32 multisampled pixel samples per clock cycle. With alpha blending,
z-test, and z-write enabled, this is equivalent to having 256 GB/sec of
effective bandwidth! The important thing is that frame buffer bandwidth will
never slow down the Xenon GPU.
Audio
The Xenon CPU is a superb processor for audio, particularly with its massive
mathematical horsepower and vector register set. The Xenon CPU can process
and encode hundreds of audio channels with sophisticated per-voice and
global effects, all while using a fraction of the power of a single CPU
core.
The Xenon system south bridge also contains a key hardware component for
audio-XMA decompression. XMA is the native Xenon compressed audio format,
based on the WMA Pro architecture. XMA provides sound quality higher than
ADPCM at even better compression ratios, typically 6:1-12:1. The south
bridge contains a full silicon implementation of the XMA decompression
algorithm, including support for multichannel XMA sources. XMA is processed
by the south bridge into standard PCM format in RAM. All other sound
processing (sample rate conversion, filtering, effects, mixing, and
multispeaker encoding) happens on the Xenon CPU.
The lowest-level Xenon audio software layer is XAudio, a new API designed
for optimal digital signal processing. The Xbox Audio Creation Tool (XACT)
API from Xbox is also supported, along with new features such as conditional
events, improved parameter control, and a more flexible 3D audio model.
Input/Output
As with Xbox, Xenon is designed to be a multiplayer console. It has built-in
networking support including an Ethernet 10/100-BaseT port. It supports up
to four controllers. From an audio/video standpoint, Xenon will support all
the same formats as Xbox, including multiple high-definition formats up
through 1080i, plus VGA output.
In order to provide greater flexibility and support a wider variety of
attached devices, the Xenon console includes standard USB 2.0 ports. This
feature allows the console to potentially host storage devices, cameras,
microphones, and other devices.
Storage
The Xenon console is designed around a larger world view of storage than
Xbox was. Games will have access to a variety of storage devices, including
connected devices (memory units, USB storage) and remote devices (networked
PCs, Xbox LiveT). At the time of this writing, the decision to include a
built-in hard disk in every Xenon console has not been made. If a hard disk
is not included in every console, it will certainly be available as an
integrated add-on component.
Xenon supports up to two attached memory units (MUs). MUs are connected
directly to the console, not to controllers as on Xbox. The initial size of
the MUs is 64 MB, although larger MUs may be available in the future. MU
throughput is expected to be around 8 MB/sec for reads and 1 MB/sec for
writes.
The Xenon game disc drive is a 12× DVD, with an expected outer edge
throughput of 16+ MB/sec. Latency is expected to be in the neighborhood of
100 ms. The media format will be similar to Xbox, with approximately 6 GB of
usable space on the disk. As on Xbox, media will be stored on a single side
in two 3 GB layers.
Industrial Design
The Xenon industrial design process is well under way, but the final look of
the box has not been determined. The Xenon console will be smaller than the
Xbox console.
The standard Xenon controller will have a look and feel similar to the Xbox
controller. The primary changes are the removal of the Black and White
buttons and the addition of shoulder buttons. The triggers, thumbsticks,
D-pad, and primary buttons are essentially unchanged. The controller will
support vibration.
Xenon Development Kit
The Xenon development environment follows the same model as for Xbox. Game
development occurs on the PC. The resulting executable image is loaded by
the Xenon development kit and remotely debugged on the PC. MS® Visual
Studio® version 7.1 continues as the development environment for Xenon.
The Xenon compiler is based on a custom PowerPC back end and the latest MS®
Visual C++® front end. The back end uses technology developed at MS for
Windows NT on PowerPC. The Xenon software group includes a dedicated team of
compiler engineers updating the compiler to support Xenon-specific CPU
extensions. This team is also heavily focused on optimization work.
The Xenon development kit will include accurate DVD emulation technology to
allow developers to very precisely gauge the effects of the retail console
disc drive.
Miscellaneous Xenon Hardware Notes
Some additional notes:
..Xenon is a big-endian system. Both the CPU and GPU process memory in
big-endian mode. Games ported from little-endian systems such as the Xbox or
PC need to account for this in their game asset pipeline.
..Tapping into the power of the CPU is a daunting task. Writing multithreaded
game engines is not trivial. Xenon system software is designed to take
advantage of this processing power wherever possible. The Xbox Advanced
Technology Group (ATG) is also exploring a variety of techniques for
offloading graphics work to the CPU.
..People often ask if Xenon can be backward compatible with Xbox. Although
the architecture of the two consoles is quite different, Xenon has the
processing power to emulate Xbox. Whether Xenon will be backward compatible
involves a variety of factors, not the least of which is the massive
development and testing effort required to allow Xbox games run on Xenon.
accurate, though some changes will have occured by the time the final
machine ships)
Xenon Hardware Overview
By Pete Isensee, Development Lead, Xbox Advanced Technology Group
This documentation is an early release of the final documentation, which may
be changed substantially prior to final commercial release, and is
confidential and proprietary information of MS Corporation. It is disclosed
pursuant to a nondisclosure agreement between the recipient and MS.
"Xenon" is the code name for the successor to the Xbox® game console from
MS. Xenon is expected to launch in 2005. This white paper is designed to
provide a brief overview of the primary hardware features of the console
from a game developer's standpoint.
Caveats
In some cases, sizes, speeds, and other details of the Xenon console have
not been finalized. Values not yet finalized are identified with a "+" sign,
indicating that the numbers may be larger than indicated here. At the time
of this writing, the final console is many months from entering production.
Based on our experience with Xbox, it's likely that some of this information
will change slightly for the final console.
For additional information on various hardware components, see the other
relevant white papers.
Hardware Goals
Xenon was designed with the following goals in mind:
..Focus on innovation in silicon, particularly features that game developers
need. Although all Xenon hardware components are technologically advanced,
the hardware engineering effort has concentrated on digital performance in
the CPU and GPU.
..Maximize general purpose processing performance rather than fixed-function
hardware. This focus on general purpose processing puts the power into the
Xenon software libraries and tools. Rather than being hamstrung by
particular hardware designs, software libraries can support the latest and
most efficient techniques.
..Eliminate the performance issues of the past. On Xbox, the primary
bottlenecks were memory and CPU bandwidth. Xenon does not have these
limitations.
Basic Hardware Specifications
Xenon is powered by a 3.5+ GHz IBM PowerPC processor and a 500+ MHz ATI
graphics processor. Xenon has 256+ MB of unified memory. Xenon runs a custom
operating system based on MS® Windows NT®, similar to the Xbox operating
system. The graphics interface is a superset of MS® Direct3D® version 9.0.
CPU
The Xenon CPU is a custom processor based on PowerPC technology. The CPU
includes three independent processors (cores) on a single die. Each core
runs at 3.5+ GHz. The Xenon CPU can issue two instructions per clock cycle
per core. At peak performance, Xenon can issue 21 billion instructions per
second.
The Xenon CPU was designed by IBM in close consultation with the Xbox team,
leading to a number of revolutionary additions, including a dot product
instruction for extremely fast vector math and custom security features
built directly into the silicon to prevent piracy and hacking.
Each core has two symmetric hardware threads (SMT), for a total of six
hardware threads available to games. Not only does the Xenon CPU include the
standard set of PowerPC integer and floating-point registers (one set per
hardware thread), the Xenon CPU also includes 128 vector (VMX) registers per
hardware thread. This astounding number of registers can drastically improve
the speed of common mathematical operations.
Each of the three cores includes a 32-KB L1 instruction cache and a 32-KB L1
data cache. The three cores share a 1-MB L2 cache. The L2 cache can be
locked down in segments to improve performance. The L2 cache also has the
very unusual feature of being directly readable from the GPU, which allows
the GPU to consume geometry and texture data from L2 and main memory
simultaneously.
Xenon CPU instructions are exposed to games through compiler intrinsics,
allowing developers to access the power of the chip using C language
notation.
GPU
The Xenon GPU is a custom 500+ MHz graphics processor from ATI. The shader
core has 48 Arithmetic Logic Units (ALUs) that can execute 64 simultaneous
threads on groups of 64 vertices or pixels. ALUs are automatically and
dynamically assigned to either pixel or vertex processing depending on load.
The ALUs can each perform one vector and one scalar operation per clock
cycle, for a total of 96 shader operations per clock cycle. Texture loads
can be done in parallel to ALU operations. At peak performance, the GPU can
issue 48 billion shader operations per second.
The GPU has a peak pixel fill rate of 4+ gigapixels/sec (16 gigasamples/sec
with 4× antialiasing). The peak vertex rate is 500+ million vertices/sec.
The peak triangle rate is 500+ million triangles/sec. The interesting point
about all of these values is that they're not just theoretical-they are
attainable with nontrivial shaders.
Xenon is designed for high-definition output. Included directly on the GPU
die is 10+ MB of fast embedded dynamic RAM (EDRAM). A 720p frame buffer fits
very nicely here. Larger frame buffers are also possible because of
hardware-accelerated partitioning and predicated rendering that has little
cost other than additional vertex processing. Along with the extremely fast
EDRAM, the GPU also includes hardware instructions for alpha blending,
z-test, and antialiasing.
The Xenon graphics architecture is a unique design that implements a
superset of Direct3D version 9.0. It includes a number of important
extensions, including additional compressed texture formats and a flexible
tessellation engine. Xenon not only supports high-level shading language
(HLSL) model 3.0 for vertex and pixel shaders but also includes advanced
shader features well beyond model 3.0. For instance, shaders use 32-bit IEEE
floating-point math throughout. Vertex shaders can fetch from textures, and
pixel shaders can fetch from vertex streams. Xenon shaders also have the
unique ability to directly access main memory, allowing techniques that have
never before been possible.
As with Xbox, Xenon will support precompiled push buffers ("command buffers"
in Xenon terminology), but to a much greater extent than the Xbox console
does. The Xbox team is exposing and documenting the command buffer format so
that games are able to harness the GPU much more effectively.
In addition to an extremely powerful GPU, Xenon also includes a very
high-quality resize filter. This filter allows consumers to choose whatever
output mode they desire. Xenon automatically scales the game's output buffer
to the consumer-chosen resolution.
Memory and Bandwidth
Xenon has 256+ MB of unified memory, equally accessible to both the GPU and
CPU. The main memory controller resides on the GPU (the same as in the Xbox
architecture). It has 22.4+ GB/sec aggregate bandwidth to RAM, distributed
between reads and writes. Aggregate means that the bandwidth may be used for
all reading or all writing or any combination of the two. Translated into
game performance, the GPU can consume a 512×512×32-bpp texture in only 47
microseconds.
The front side bus (FSB) bandwidth peak is 10.8 GB/sec for reads and 10.8
GB/sec for writes, over 20 times faster than for Xbox. Note that the 22.4+
GB/sec main memory bandwidth is shared between the CPU and GPU. If, for
example, the CPU is using 2 GB/sec for reading and 1 GB/sec for writing on
the FSB, the GPU has 19.4+ GB/sec available for accessing RAM.
Eight pixels (where each pixel is color plus z = 8 bytes) can be sent to the
EDRAM every GPU clock cycle, for an EDRAM write bandwidth of 32 GB/sec. Each
of these pixels can be expanded through multisampling to 4 samples, for up
to 32 multisampled pixel samples per clock cycle. With alpha blending,
z-test, and z-write enabled, this is equivalent to having 256 GB/sec of
effective bandwidth! The important thing is that frame buffer bandwidth will
never slow down the Xenon GPU.
Audio
The Xenon CPU is a superb processor for audio, particularly with its massive
mathematical horsepower and vector register set. The Xenon CPU can process
and encode hundreds of audio channels with sophisticated per-voice and
global effects, all while using a fraction of the power of a single CPU
core.
The Xenon system south bridge also contains a key hardware component for
audio-XMA decompression. XMA is the native Xenon compressed audio format,
based on the WMA Pro architecture. XMA provides sound quality higher than
ADPCM at even better compression ratios, typically 6:1-12:1. The south
bridge contains a full silicon implementation of the XMA decompression
algorithm, including support for multichannel XMA sources. XMA is processed
by the south bridge into standard PCM format in RAM. All other sound
processing (sample rate conversion, filtering, effects, mixing, and
multispeaker encoding) happens on the Xenon CPU.
The lowest-level Xenon audio software layer is XAudio, a new API designed
for optimal digital signal processing. The Xbox Audio Creation Tool (XACT)
API from Xbox is also supported, along with new features such as conditional
events, improved parameter control, and a more flexible 3D audio model.
Input/Output
As with Xbox, Xenon is designed to be a multiplayer console. It has built-in
networking support including an Ethernet 10/100-BaseT port. It supports up
to four controllers. From an audio/video standpoint, Xenon will support all
the same formats as Xbox, including multiple high-definition formats up
through 1080i, plus VGA output.
In order to provide greater flexibility and support a wider variety of
attached devices, the Xenon console includes standard USB 2.0 ports. This
feature allows the console to potentially host storage devices, cameras,
microphones, and other devices.
Storage
The Xenon console is designed around a larger world view of storage than
Xbox was. Games will have access to a variety of storage devices, including
connected devices (memory units, USB storage) and remote devices (networked
PCs, Xbox LiveT). At the time of this writing, the decision to include a
built-in hard disk in every Xenon console has not been made. If a hard disk
is not included in every console, it will certainly be available as an
integrated add-on component.
Xenon supports up to two attached memory units (MUs). MUs are connected
directly to the console, not to controllers as on Xbox. The initial size of
the MUs is 64 MB, although larger MUs may be available in the future. MU
throughput is expected to be around 8 MB/sec for reads and 1 MB/sec for
writes.
The Xenon game disc drive is a 12× DVD, with an expected outer edge
throughput of 16+ MB/sec. Latency is expected to be in the neighborhood of
100 ms. The media format will be similar to Xbox, with approximately 6 GB of
usable space on the disk. As on Xbox, media will be stored on a single side
in two 3 GB layers.
Industrial Design
The Xenon industrial design process is well under way, but the final look of
the box has not been determined. The Xenon console will be smaller than the
Xbox console.
The standard Xenon controller will have a look and feel similar to the Xbox
controller. The primary changes are the removal of the Black and White
buttons and the addition of shoulder buttons. The triggers, thumbsticks,
D-pad, and primary buttons are essentially unchanged. The controller will
support vibration.
Xenon Development Kit
The Xenon development environment follows the same model as for Xbox. Game
development occurs on the PC. The resulting executable image is loaded by
the Xenon development kit and remotely debugged on the PC. MS® Visual
Studio® version 7.1 continues as the development environment for Xenon.
The Xenon compiler is based on a custom PowerPC back end and the latest MS®
Visual C++® front end. The back end uses technology developed at MS for
Windows NT on PowerPC. The Xenon software group includes a dedicated team of
compiler engineers updating the compiler to support Xenon-specific CPU
extensions. This team is also heavily focused on optimization work.
The Xenon development kit will include accurate DVD emulation technology to
allow developers to very precisely gauge the effects of the retail console
disc drive.
Miscellaneous Xenon Hardware Notes
Some additional notes:
..Xenon is a big-endian system. Both the CPU and GPU process memory in
big-endian mode. Games ported from little-endian systems such as the Xbox or
PC need to account for this in their game asset pipeline.
..Tapping into the power of the CPU is a daunting task. Writing multithreaded
game engines is not trivial. Xenon system software is designed to take
advantage of this processing power wherever possible. The Xbox Advanced
Technology Group (ATG) is also exploring a variety of techniques for
offloading graphics work to the CPU.
..People often ask if Xenon can be backward compatible with Xbox. Although
the architecture of the two consoles is quite different, Xenon has the
processing power to emulate Xbox. Whether Xenon will be backward compatible
involves a variety of factors, not the least of which is the massive
development and testing effort required to allow Xbox games run on Xenon.