Most Detailed 'Leaked' Xbox 2 Spec Emerges - Must Read!

Another week, another spec sheet - this time with added salt.

Posted by Staff
Most Detailed 'Leaked' Xbox 2 Spec Emerges - Must Read!
We received this morning perhaps the most detailed essay to date purporting to be a leaked internal Xbox 2 memo from Microsoft.

The spec claims to be by Pete Isensee, Development Lead, Xbox Advanced Technology Group.

Here is the entire document reproduced in full:

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.

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.

  • Maximise 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.

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.

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.

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.

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.

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 Live). 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
  • 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.

So, another week, another Xbox 2 spec 'leak'. It begs the question, where are all the Revolution and PlayStation 3 spec leaks...

Expect updates as soon as they are revealed, right here on SPOnG.


Viclo 23 Jun 2004 17:55
I think Microsoft will change things up a bit from what's here. Who knows...maybe MS even "leaked" it on purpose and dummed the specs down a bit so that they can better take on the competition at a later date. Either that or someone just leaked the damn thing. In either case...I'm pretty impressed. Let's see what Nintendo and Sony shell out.
mrnull 23 Jun 2004 17:57
Is this for real? The writing certainly looks soulless enough to be authentic. I wish I remembered more from my PC Hardware classes...

Anyway, assuming it is true: MS better include a damn harddrive! The XBox is a great buy now for $150, mainly because the HD and Broadband Adapter are included. You can't say that for the PS2.

Back when N64 games started to require that extra memory stick (can't remember what it was called,) I and my friends felt alienated. If at all possible the industry needs to stay away from add-ons; the PS2 HD for example. If you have a device that will be constantly used by game developers, put it in the console! I always feel tricked when I have to go out and buy new gear + the game.
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Joji 23 Jun 2004 18:29
All the stuff is very confusing, had a headache just goin through it all. Specs sound very nice and I'm sure they will be. The thing is theres only so far graphics and sound can be tinkered with so when i read stuff like the from any company it's confusing if not made short and sweet. This was leaked so it wasn't meant for us to understand, unless you are a serious tech monkey.

I'm surprised that MS don't encourage folk to hack/crack their Xboxs. It's clearly not something everyone would do, but you have to admire peoples enginuity and persistence to get what they want. I think the same will happen to Xbox2, cause people just love to wind up MS. What they do with their console is their business once bought, and MS don't have to like.

I'm sure Xbox2 will be nice, but instead of focusing on the CPU and GPU, they should be focusing on getting the design right this time.

jedisb 23 Jun 2004 21:27
mrnull wrote:

>Is this for real? The writing certainly looks
>soulless enough to be authentic. I wish I
>remembered more from my PC Hardware classes...

I think it is fake. And my reasoning has nothing to do with the specs, etc. In the supposed document the MS guy, Pete Isenee, uses the letter 's' in spellling maximise (second bullet point under "Hardware Goals". That is not the way that word is spelled in the United Sates. It is spelled 'maximize'. The British use 's' where we use 'z'.

I found the guy's personal web site here:

On that page he spells optimize with a 'z' and not a 's'. It looks to me that this was faked by someone in Britain.

config 24 Jun 2004 13:48
The Register has picked up on this and added ...

> Interestingly, it also mentions the GPU's ability
> to snoop the CPU's L2 cache, apparently a
> feature little-known outside the developer
> community until now

Why would this feature be even a little known outside of development circles? I'm fairly geek, and like to keep and eye on developer, erm, developments. You know what? I don't give a rats ass about this feature.

In fact, by tomorrow I'll have forgotten all about something to do with L2 buttons and GDP or cash or something.
FryingLizard 24 Jun 2004 17:56
The thing with the GPU having access to the L2 cache is actually a really splendid idea. This way it can get fed from two separate physical busses at the same time (main memory bus and l2 cache bus).

Better yet the L2 cache (as it is a decent-ish sized 1mb and much faster than main memory) is the ideal place to be doing this sort of short-term buffering of geometry data - frequently when assembling complex polygon lists (e.g. featuring a lot of multipass or whatever) you really need to be able to keep a decent number of vertices lying around in fast memory, for clipping, caching, whatever.

As you're doing all your math with the main CPUs (which sounds like a really fun amount of horsepower BTW), and they have the L2 cache anyway, why bother doing the slow round-trip out to be written to DRAM and later read back to the GPU?

It's a great idea but I wonder how much of a PITA it will be to share the cache this way as a GPU pipeline and a general CPU cache.

It would seem tempting (and is supported) to lock half of it down and use it as a geometry pipe to the GPU, but then you're going to impact general purpose CPU performance bigtime, Esp. with so many CPU hardware threads running code from all over the place as the same time - remember that all CPUs share the same L2 cache!

I suspect people will wish the L2 cache was much bigger than 1Mb, but hey.. ;-)

Nice spec. Embedded DRAM in the GPU is your friend and the hardware resources being dynamically allocated between pixel and vertex shaders looks like a winner too. Yay.
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