Graphics EngineLooks good on paper.
XBA™ is the result of those efforts. XBA™ is a tightly coupled graphics engine that encompasses high speed embedded memory (EDRAM) with a 512 bit memory interface that is 4X wider than the industry's current crop of 128 bit interface. This memory is used to the fullest by an 8-texel pipeline for the 3D processor market. These two components go hand in hand. Without the huge bandwidth of the embedded memory the 8-texel engine would stall and not be efficient or practical.
In XBA the memory bus can be 512-bits wide because the memory is embedded on the same die with the rendering core. So how much memory bandwidth is required if the 3D-graphics chip renders 600 million pixels, 1.2 Gigatexels/sec using a dual texturing pipeline? Naturally, we won't be satisfied with 16-bit color, which is simply unacceptable when compared with 32-bit true color. We also want a 32-bit floating point depth buffer to eliminate any artifacts common with a 16-bit depth buffer.
For each rendered pixel (on average) we read the depth value and write the color and depth value back to the frame buffer. This means that for each pixel we must access 12 bytes of memory. 600M by 12 is 7.2 GB/s. But this is not all, we also have to count the bandwidth required by the video refresh unit, at 1024x768x85 Hz that's 64 MB/s. We also need to read textures and that's 500 MB/s to 2 Gigabytes/sec. In total, close to the 10 GB/s memory bandwidth and that's just for 600M pixels/ 1.2 Gigatexels! As the performance targets increase the memory bandwidth requirements scale accordingly.