E3 2005 - Day 2: More Details Emerge on Console GPUs

This year's E3 has been, overall, a pretty big letdown. The show itself hasn't been very interesting simply because it's mostly current-gen titles and hardware. For the E3 just before the launch of Microsoft's Xbox 360, we were a bit disappointed not to see any working hardware at the show outside of the ATI booth.

With a relatively light schedule thanks to the small size of the show, we were able to spend quite a bit of time digging deeper on the two highlights of this year's E3 - ATI's Xbox 360 GPU, and NVIDIA's RSX, the GPU powering the PlayStation 3.

Given that both of the aforementioned GPU designs are very closely tied to their console manufacturers, information flow control was dictated by the console makers, not the GPU makers. And unfortunately, neither Microsoft or Sony were interested in giving away more information than their ridiculously light press releases.

Never being satisfied with the norm, we've done some digging and this article is what we've managed to put together. Before we get started, we should mention a few things:

1) Despite our best efforts, information will still be light because of the strict NDAs imposed by Microsoft and Sony on the GPU makers.

2) Information on NVIDIA's RSX will be even lighter because it is the more PC-like of the two solutions and as such, a lot of its technology overlaps with the upcoming G70 GPU, an item we currently can't talk about in great detail.

With those items out of the way, let's get started, first with what has already been announced.

The Xbox 360 GPU, manufactured by ATI, is the least PC-like of the two GPUs for a number of reasons, the most obvious being its 10MB of embedded DRAM. Microsoft announced that the 10MB of embedded DRAM has 256GB/s of bandwidth availble to it; keep this figure in mind, as its meaning isn't as clear cut as it may sound.

The GPU operates at 500MHz and has a 256-bit memory interface to 512MB of 700MHz GDDR3 system memory (that is also shared with the CPU).

Another very prominent feature of the GPU is that it implements ATI's first Unified Shader Architecture, meaning that there are no longer any discrete pixel and vertex shader units, they are instead combined into a set of universal execution units that can operate on either pixel shader or vertex shader instructions. ATI is characterizing the width of the Xbox 360 GPU as being 48 shader pipelines; we should caution you that these 48 pipelines aren't directly comparable to current 16-pipeline GPUs, but rest assured that the 360 GPU should be able to shade and texture more pixels per clock than ATI's fastest present-day GPU.

Now let's move on to NVIDIA's RSX; the RSX is very similar to a PC GPU in that it features a 256-bit connection to 256MB of local GDDR3 memory (operating at 700MHz). Much like NVIDIA's Turbo Cache products, the RSX can also render to any location in system memory, giving it access to the full 256MB of system memory on the PS3 as well.

The RSX is connected to the PlayStation 3's Cell CPU by a 35GB/s FlexIO interface and it also supports FP32 throughout the pipeline.

The RSX will be built on a 90nm process and features over 300 million transistors running at 550MHz.

Between the two GPUs there's barely any information contained within Microsoft's and Sony's press launches, so let's see if we can fill in some blanks.