As any PC gamer will tell you, the only thing more important than the CPU is the graphics chipset – here Microsoft switched allegiance from nVidia (used in the original Xbox) to arch-rival ATI. The ATI GPU – codenamed Xenos – is a very interesting chip. In essence you’ve got a GPU manufactured using a 90nm process running at 500MHz – but it’s not quite that simple. Although many people out there (myself included) expected the GPU in the X360 to be an almost identical part to a PC graphics card, it really isn’t. The GPU is supported by a second die containing 10MB of embedded DRAM – this is where that lovely anti-aliasing is processed.
There is 512MB of GDDR3 memory to play with, running at 700MHz, but this is shared between the system and the GPU. What’s interesting here is that the memory controller is actually embedded in the GPU so there is no separate northbridge – much like an Athlon 64 system, where the memory controller is integrated into the CPU. Continuing the integrated trend, Xenos also implements a unified shader model. Whereas PC graphics chips will have a number of vertex shaders and a number of pixel shaders, Xenos just has shaders. These shaders can be either pixel shaders or vertex shaders – this is a dynamic process and should avoid vertex shader or pixel shader bottlenecks that can occur with PC hardware. I guess this ties in well with ATI’s drive for efficient execution over the number of pipelines – something that the company was pushing hard at the X1000 launch in October.
Unlike the PS3 which will be sporting a Blu-ray optical drive, Microsoft has stuck with a standard DVD drive for the X360. I would imagine that this decision was driven by timing – if Microsoft had wanted to implement an “next generation” optical device, there is no way that the X360 would be in the shops right now. I can’t say that I’m that worried about having a DVD drive in the box, since a DVD-9 should provide more than enough storage for the majority of games – unless the developer wants to throw hours of HD cut scenes into the mix. Of course the other argument for having a Blu-ray or HD-DVD drive in a console is that you’ll be able to watch HD movies on it, but to be honest I would rather have a separate player for movies anyway.