Are there any differences between the RV515 chip for the PC and the GPU that will be used for the Xbox 360?

Yes, there are huge differences. The Xbox 360 GPU is designed for the Xbox 360 only, and it is not comparable to any existing or soon the be launched PC products.

Could you briefly describe the differences between the Xenon chipset and NVIDIA’s RSX chipset which is planned for Sony’s Playstation 3?

Sorry, but all I know about the Playstation 3 GPU so far is limited to the official information and a lot of rumors, and I would not like to make this kind of comparison based mainly on rumors. I am afraid that we will have to wait with these comparisons until we know the specs of both products.

How is efficiency affected by a single unified pipeline for pixel and vertex (Xbox 360)?

The Xbox 360 GPU is the only GPU with a unified shader architecture. Unified Shaders offer more flexibility, essentially providing more pixel or more vertex shading power when needed. This does of course have an effect on efficiency as you don’t have vertex shader units running idle while the pixel shaders are all under heavy load. And of course, it has the advantage that shader programs that need to calculate vertex and pixel operations do not have to go from one shader unit to another, so the performance of features such as Displacement Mapping improve tremendously with a unified shader architecture.

Microsoft’s Xbox 360 will be equipped with an eDRAM Die unit, connected to the GPU. What is the functionality of this unit?

The GPU has access to 10MB of eDRAM dedicated to graphics. These 10MB are not simply for storage, but also take over some of the graphics processing tasks required for Anti-Aliasing, Z, Alpha or Stencil. So essentially, we are talking about intelligent eDRAM, rather than just a big chunk of memory for storage of data.

According to sources, Microsoft will work with NVIDIA in order to emulate Xbox's Intel CPU on the 360's multiple IBM PowerPC cores, and will also emulate the NVIDIA chip to some extent on the ATI graphics chip in the 360. What are your comments on the backwards compatibility issues of the Xbox 360 in connection with the earlier Xbox game titles?

This is a question that I would not like to get into. While I am sure that we work with Microsoft on this, it is mainly a Microsoft project for which I can’t supply comments as I don’t have the full picture. Microsoft or a game developer would be the better spokesperson on this.