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Xbox in the test: Microsoft dares to revolt against Sony

Xbox in the test: Microsoft dares to revolt against Sony

XGPU

As is well known, the XGPU comes from Nvidia and it is she who is decisive for whether the box is really the next one Generation of the game console n embodies. The code name NV2A makes it clear that the XGPU is not too far removed from GeForce 3 (NV20) and GeForce 4 (NV25) . As with the processor, the architecture of the graphics chip has been adapted to the special needs of the console. While it is clocked lower than the GF3 Ti500 at 233MHz (PS2 - 147MHz), it has all GF3 cards in that, like the GF4, it comes with two vertex shaders instead of one. Four rendering pipelines and the pixel shader unit are now a matter of course. If you now look at the components that are crucial for performance, you might ask yourself how a PIII 733 with 64MB RAM and a revamped GeForce3 should represent the platform of the future. Why should a game like Halo, which triggered the thought of upgrading in many, run on these somewhat outdated components? What is the advantage of the Xbox over a PC? In terms of performance, almostnothing at all, is the sobering answer. But, it is a console, a closed system.

For the next three to five years, the software developers of Xbox games can rely one hundred percent on the fact that every single potential buyer has the same performance reserves in their system has, and for the most part in the XGPU. These are reserves that every owner of a PC with GeForce4 can surpass, except that they will probably lie idle in the PC for some time. For the Xbox, on the other hand, regardless of compatibility, it is possible to program in such a way that possible bottlenecks in processor and memory architecture are avoided and all the strengths of the GPU are used.

Xbox from the front
Xbox from behind

On the hardware side, these strengths are above all the already mentioned two vertex shaders and the programmable pixel shader. Both must be used to relieve the CPU of a large part of its work. Just like the Texture & Lighting unit, they also mean that the majority of the data is concentrated on the 6.4GB/s wide connection between the GPU and memory. In order not to overload this bandwidth, there are a few other features of the XGPU. In particular, the skilful use of the Z-buffer, which determines the “depth” at which a point is located in the image, allows you to save a lot of bandwidth. For example, unnecessary access to hidden textures can be avoided and up to 75% of the texture bandwidth can be saved. Of course, the use of the buffer itself also requires bandwidth for this. However, this can in turn be reduced by almost two thirds thanks to the automatic Z compression of the XGPUwill. The fact remains that with a resolution of 640x480, full-scene antialiasing (FSAA) is mandatory. If the box with 4xFSAA reaches its limits, in extreme cases there is still the option of switching down from 32-bit Z-buffering to 16-bit W-buffering.

Xbox from above

At least as important as the hardware features is the DirectX 8 support of the XGPU, the use of which is considerably simplified by using a modified Windows 2000 operating system. This is also nothing that a PC with GeForce3 cannot offer, only very few PC games have been using DX8 effectively so far, while the Xbox game developers, for example, can plan the texture compression capabilities of DirectX 8 and squeeze them out to the last.

So you can say that the components of the Xbox, the CPU, the UMA and the XGPU, which are decisive for the performance, are all not dimensioned in such a way that they could easily outperform the performance of any PC. Rather, the closed system concept, by allowing careful programmers to take full advantage of the Xbox's strengths and bypassing its weaknesses, is responsible for the fact that, in the end, games on this novel console could keep up with PC games for several years to come which the PS2 should very soon leave far behind.

On the next page: Further components

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