Lots More Compute, a Leetle More Texturing

NVIDIA's GT200 GPU has a significant increase in computational power thanks to its 240 streaming processors, up from 128 in the previous G80 design. As a result, NVIDIA's GT200 GPU showcases a tremendous increase in transistor count over its previous generation architecture (1.4 billion up from 686 million in G80).

The increase in compute power of GT200 is not mirrored however in the increase in texture processing power. On the previous page we outlined how the Texture/Processing Clusters went from two Shader Multiprocessors to three, and how there are now a total of ten TPCs in the chip up from 8 in the GeForce 8800 GTX.

In the original G80 core, used in the GeForce 8800 GTX NVIDIA's texture block looked like this:

In each block you had 4 texture address units and 8 texture filtering units.

With the move to G92, used in the GeForce 8800 GT, 8800 GTS 512 and 9800 GTX, NVIDIA doubled the number of texture address units and achieved a 1:1 ratio of address/filtering units:

With GT200 in the GeForce GTX 280/260, NVIDIA kept the address-to-filtering ratio at 1:1 but increased the ratio of SPs to texture processors:

In the previous designs you'd have 8 address and 8 filtering units per TPC (or 16 streaming processors), in the GT200 you have the same 8 address and 8 filtering units but for a larger TPC with 24 SPs.

Here's how the specs stand up across the generations:

 NVIDIA Architecture Comparison G80 G92 GT200
Streaming Processors per TPC 16 16 24
Texture Address Units per TPC 4 8 8
Texture Filtering Units per TPC 8 8 8
Total SPs 128 128 240
Total Texture Address Units 32 64 80
Total Texture Filtering Units 64 64 80

 

For a 87.5% increase in compute, there's a mere 25% increase in texture processing power. This ratio echoes what NVIDIA has been preaching for years: that games are running more complex shaders and are not as bound by texture processing as they were in years prior. If this wasn't true then we'd see a closer to 25% increase in performance of GT200 over G80 at the same clock rather than something much greater.

It also means that GT200's performance advantage over G80 or G92 based architectures (e.g. GeForce 9800 GTX) will be determined much by how computationally bound the games we're testing are.

The ratio of increase compute/texture power in the GT200 has been evident in NVIDIA architectures for years now, dating back to the ill-fated GeForce FX. NVIDIA sacrificed memory bandwidth on the GeForce FX, equipping it with a narrow 128-bit memory bus (compared to ATI's 256-bit interface on the Radeon 9700 Pro) and instead focused on building a much more powerful compute engine. Unfortunately, the bet was the wrong one to make at the time and the GeForce FX was hardly competitive (for more reasons than just a lack of memory bandwidth), but today we're dealing in a very different world. Complex shader programs run on each pixel on the screen and there's a definite need for more compute power in today's GPUs.

An Increase in Rasterization Throughput

In addition to the 25% increase in texture processing capabilities of the GT200, NVIDIA added two more ROP partitions to the GPU. While the GeForce 8800 GTX had six ROP partitions, each capable of outputting a maximum of 4 pixels per clock, the GT200 adds two more partitions.

With eight ROP partitions the GT200 can now output a maximum of 32 pixels per clock, up from 24 pixels per clock in the GeForce 8800 GTX and 9800 GTX.

The pixel blend rate on G80/G92 was half-speed, meaning that while you could output 24 pixels per clock, you could only blend 12 pixels per clock. Thanks to the 65nm shrink and redesign, GT200 can now output and blend pixels at full speed - that's 32 pixels per clock for each.

The end result is a non-linear performance improvement in everything from anti-aliasing and fire effects to shadows on GT200. It's an evolutionary change, but that really does sum up many of the enhancements of GT200 over G80/G92.

Building NVIDIA's GT200 Derek Gets Technical: 15th Century Loom Technology Makes a Comeback
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  • junkmonk - Monday, June 16, 2008 - link

    I can has vertex data? LMFAO, hahha that was a good laugh. Reply
  • PrinceGaz - Monday, June 16, 2008 - link

    When I looked at that, I assumed it must be a non-native English speaker who put that in the block. I'm still not entirely sure what it was trying to convey other than that the core will need to be fed with lots of vertices to keep it busy. Reply
  • Spoelie - Tuesday, June 17, 2008 - link

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  • chizow - Monday, June 16, 2008 - link

    Its going to take some time to digest it all, but you two have done it again with a massive but highly readable write-up of a new complex microchip. You guys are still the best at what you do, but a few points I wanted to make:

    1) THANK YOU for the clock-for-clock comparo with G80. I haven't fully digested the results, but I disagree with your high-low increase thresholds being dependent on solely TMU and SP. You don't mention GT200 has 33% more ROP as well which I think was the most important addition to GT200.

    2) The SP pipeline discussion was very interesting, I read through 3/4 of it and glanced over the last few paragraphs and it didn't seem like you really concluded the discussion by drawing on the relevance of NV's pipeline design. Is that why NV's SPs are so much better than ATI's, and why they perform so well compared to deep piped traditional CPUs? What I gathered was that NV's pipeline isn't nearly as rigid or static as traditional pipelines, meaning they're more efficient and less dependent on other data in the pipe.

    3) I could've lived without the DX10.1 discussion and more hints at some DX10.1 AC/TWIMTBP conspiracy. You hinted at the main reason NV wouldn't include DX10.1 on this generation (ROI) then discount it in the same breath and make the leap to conspiracy theory. There's no doubt NV is throwing around market share/marketing muscle to make 10.1 irrelevant but does that come as any surprise if their best interest is maximizing ROI and their current gen parts already outperform the competition without DX10.1?

    4) CPU bottlenecking seems to be a major issue in this high-end of GPUs with the X2/SLI solutions and now GT200 single-GPUs. I noticed this in a few of the other reviews where FPS results were flattening out at even 16x12 and 19x12 resolutions with 4GHz C2D/Qs. You'll even see it in a few of your benches at those higher (16/19x12) resolutions in QW:ET and even COD4 and those were with 4x AA. I'm sure the results would be very close to flat without AA.

    That's all I can think of for now, but again another great job. I'll be reading/referencing it for the next few days I'm sure. Thanks again!
    Reply
  • OccamsAftershave - Monday, June 16, 2008 - link

    "If NVIDIA put the time in (or enlisted help) to make CUDA an ANSI or ISO standard extention to a programming language, we would could really start to get excited."

    Open standards are coming. For example, see Apple's OpenCL, coming in their next OS release.
    http://news.yahoo.com/s/nf/20080612/bs_nf/60250">http://news.yahoo.com/s/nf/20080612/bs_nf/60250
    Reply
  • ltcommanderdata - Monday, June 16, 2008 - link

    At least AMD seems to be moving toward standardizing their GPGPU support.

    http://www.amd.com/us-en/Corporate/VirtualPressRoo...">http://www.amd.com/us-en/Corporate/VirtualPressRoo...

    AMD has officially joined Apple's OpenCL initiative under the Khronos Compute Working Group.

    Truthfully, with nVidia's statements about working with Apple on CUDA in the days leading up to WWDC, nVidia is probably on board with OpenCL too. It's just that their marketing people probably want to stick with their own CUDA branding for now, especially for the GT200 launch.

    Oh, and with AMD's launch of the FireStream 9250, I don't suppose we could see benchmarks of it against the new Tesla?
    Reply
  • paydirt - Monday, June 16, 2008 - link

    tons of people reading this article and thinking "well, performance per cost, it's underwhelming (as a gaming graphics card)." What people are missing is that GPUs are quickly becoming the new supercomputers. Reply
  • ScythedBlade - Monday, June 16, 2008 - link

    Lol ... anyone else catch that? Reply
  • Griswold - Monday, June 16, 2008 - link

    Too expensive, too power hungry and according to other reviews, too loud for too little gain.

    The GT200 could become Nvidias R600.

    Bring it on AMD, this is your big chance!
    Reply
  • mczak - Monday, June 16, 2008 - link

    G92 does not have 6 rop partitions - only 4 (this is also wrong in the diagram). Only G80 had 6.
    And please correct that history rewriting - that the FX failed against radeon 9700 had NOTHING to do with the "powerful compute core" vs. the high bandwidth (ok the high bandwidth did help), in fact quite the opposite - it was slow because the "powerful compute core" was wimpy compared to the r300 core. It definitely had a lot more flexibility but the compute throughput simply was more or less nonexistent, unless you used it with pre-ps20 shaders (where it could use its fx12 texture combiners).
    Reply

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