Terren reporting from E3I have received some details from Terren about the architecture of the Xbox 360, and more specifically, its graphics subsystem.
Firstly, while the GPU and its 10 MB of embedded DRAM are manufactured seperately, they are present on the same physical package. The embedded DRAM clocks in at 2 GHz, and provides 256 GB/s of bandwidth. It is being dubbed "intelligent memory", for it contains 192 parallel pixel processors, allowing the memory to do independant processing of its own, and not compromising the performance of the GPU. Some of this processing includes 4x anti-aliasing at 720p, dynamic shadows, stencil buffer shadows, and occlusion culling.
Since the majority of heat produced is by the GPU/memory I/O, embedded DRAM allows the GPU to be cooled by a passive heatsink, along with the system fans already present in the Xbox 360. The "regular" 512 MB of GDDR3 system/graphics memory operates at 700 MHz.
Microsoft says that through the use of the XNA tools, it takes approximately one week to port PC applications to the Xbox 360, which ought to be a boon to developers.
Here are some pictures of the ATI/Microsoft press conference slides:
