NVIDIA's GeForce 7800 GTX Hits The Ground Running
by Derek Wilson on June 22, 2005 9:00 AM EST- Posted in
- GPUs
The Pipeline Overview
First, let us take a second to run through NVIDIA's architecture in general. DirectX or OpenGL commands and HLSL and GLSL shaders are translated and compiled for the architectures. Commands and data are sent to the hardware where we go from numbers, instructions and artwork to a rendered frame.The first major stop along the way is the vertex engine where geometry is processed. Vertices can be manipulated using math and texture data, and the output of the vertex pipelines is passed on down the line to the fragment (or pixel) engine. Here, every pixel on the screen is processed based on input from the vertex engine. After the pixels have been processed for all the geometry, the final scene must be assembled based on color and z data generated for each pixel. Anti-aliasing and blending are done into the framebuffer for final render output in what NVIDIA calls the render output pipeline (ROP). Now that we have a general overview, let's take a look at the G70 itself.
The G70 GPU is quite a large IC. Weighing in at 302 million transistors, we would certainly hope that NVIDIA packed enough power in the chip to match its size. The 110nm TSMC process will certainly help with die size, but that is quite a few transistors. The actual die area is only slightly greater than NV4x. In fact, NVIDIA is able to fit the same number of ICs on a single wafer.
A glance at a block diagram of the hardware gives us a first look at the methods by which NVIDIA increased performance this time around.
The first thing to notice is that we now have 8 (up from 6) vertex pipelines. We still aren't vertex processing limited (except in the workstation market), but this 33% upgrade in vertex power will help to keep the extra pixel pipelines fed as well as handle any added vertex load developers try to throw at games in the near future. There are plenty of beautiful things that can be done with vertex shaders that we aren't seeing come about in games yet like parallax and relief mapping as well as extended use of geometry instancing and vertex texturing.
Moving on to pixel pipelines, we see a 50% increase in the number of pipelines packed under the hood. Each of the 24 pixel pipes is also more powerful than those of NV4x. We will cover just why that is a little later on. For now though, it is interesting to note that we do not see an increase in the 16 ROPs. These pipelines take the output of the fragment crossbar (which aggregates all of the pixel shader output) and finalizes the rendering process. It is here where MSAA is performed, as well as the color and z/stencil operations. Not matching the number of ROPs to the number of pixel pipelines indicates that NVIDIA feels its fill rate and ability to handle current and near future resolutions is not an issue that needs to be addressed in this incarnation of the GeForce. As NVIDIA's UltraShadow II technology is driven by the hardware's ability to handle twice as many z operations per clock when a z only pass is performed, this also means that we won't see improved performance in this area.
If NVIDIA is correct in their guess (and we see no reason they should be wrong), we will see increasing amounts of processing being done per pixel in future titles. This means that each pixel will spend more time in the pixel pipeline. In order to keep the ROPs busy in light of a decreased output flow from a single pixel pipe, the ratio of pixel pipes to ROPs can be increased. This is in accord with the situation we've already described.
ROPs will need to be driven higher as common resolutions increase. This can also be mitigated by increases in frequency. We will also need more ROPs as the number pixel pipelines are able to saturate the fragment crossbar in spite of the increased time a pixel spends being shaded.
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Alx - Wednesday, June 22, 2005 - link
Face it, this launch isn't gonna hurt anyone except people with minds too small to accept that there is simply one more option than there was before. If you liked pc gaming yesterday, then there is no reason why this launch should make you stop liking it today. Unless you're a retarded buttbaby who can't handle choices. In that case please get a console and stop coming to this site.mlittl3 - Wednesday, June 22, 2005 - link
#82, WesleyWell that sucks that ya'll have lost your web editor for awhile. Especially when there is so much cool hardware coming out around now. In our research lab, we pass around our publications and conference posters to others in the group so that a fresh pair of eyes see them before they go live or to the journal editor. But of course, everyone else at AT is also busy so oh well.
Good work guys and I look forward to the "new CPU speed bump" article (or FX-57 for those not under NDAs).
Mark
PS. If ya'll have an opening for another web editor, you should hire #84 (ironchefmorimoto). I hear he can cook really well.
AtaStrumf - Wednesday, June 22, 2005 - link
Nicely corrected Derek, I think there are just a few typos left, like this one (**):Page 20
Power Consumption
We measured power consumption between the power supply and the wall. This multiplies essentially amplifies any differences in power draw because the powersupply is not 100% efficient. Ideally we would measure power draw of the card, but it is very difficult **determine** to determine the power draw from both the PCIe bus and the 12V molex connector.
AND a few double "Performances" in the title (Performance Performance) starting with page 10.
Nice card nVidia!!! I hope ATi isn't too far behind though. Crossfire --> cheap SLi ;-) I need a nice midrange product out by September when it'll be time to upgrade to a nice E6 stepping S939 A64 and something to take the place of my sweet old GF2 MX (I'm not kidding, I sold my 6600GT AGP, and now I'm waiting for the right time to move to PCIe).
IronChefMoto - Wednesday, June 22, 2005 - link
Amen -- you guys work hard on your articles. Keep up the great work. And don't f*cking bother the web editor. We...er...they don't get enough vacation as it is.IronChefMorimoto
(another web editor who needs a break)
Wesley Fink - Wednesday, June 22, 2005 - link
Derek was too modest to mention this in his comments, but I think you should know all the facts. Our Web Editor is on vacation and we are all doing our own HTML and editing for the next 10 days. In our usual process, the article goes from an Editor to the Web Editor who codes the article, checks the grammar, and checks for obvious content errors. Those steps are not in the loop right now.The next thing is NDA's and launches. We are always under the gun for launches, and lead times seem to get shorter and shorter. Derek was floating questions and graphs last night at 3 to 4 AM with an NDA of 9AM. Doing 21 pages of meaningful commentary in a short time frame, then having to code it in HTML (when someone else normally handles that task), is not as easy as it might appear.
I do know Derek as a very conscientious Editor and I would ask that you please give him, and the rest of us, a little slack this next week and a half. If you see errors please email the Editor of the article instead of making it the end of the world in these comments. I assure you we will fix what is wrong. That approach, given the short staff, would be a help to all of us. We all want to bring you the information and quality reviews you want and expect from AnandTech.
IronChefMoto - Wednesday, June 22, 2005 - link
#79 -- But why wouldn't it be a high quality article, mlittl3? I thought you told me that AT was infallible? Hmmm? ;-)Houdani - Wednesday, June 22, 2005 - link
Thanks for the refresh, Derek. I went back and took a peek at the revised graphs. I have a couple of comments on this article before you move on to the next project.>> When the Splinter Cell page was refreshed, the graph for 20x15x4 apparently disappeared.
>> When you removed the SLI's from the Guild War page, it looks like the 7800GTX changed from 50.5 to 55.1 (which is the score previously given to the 6800 Ultra SLI).
>> Several of the pages have scores for no AA benches listed first, while other pages have scores for the 4xAA listed first. While the titles for the graphs are correct, it's a little easier to read when you stay consistent in the ordering. This is a pretty minor nit-pick, though.
>> Thanks for updating the transparency images to include mouseover switches ... quite handy.
fishbits - Wednesday, June 22, 2005 - link
"They priced themselves into an extremely small market, and effectively made their 6800 series the second tier performance cards without really dropping the price on them. I'm not going to get one, but I do wonder how this will affect the company's bottom line."The 6800s were "priced into an extremely small market." How'd that line turn out? I don't imagine they've released this product with the intention of losing money overall. Why do you think retailers bought them? Because they know the cards won't sell and they're happy to take the loss? It's already been proven that people will pay for you to develop and sell a $300, wait $400, wait $500 video card. It's already been proven that people will pay a $100+ premium for cards that are incrementally better, not just a generation better. Sounds like this target is a natural, especially knowing it'll eventually fall into everyone else's purchasing ability.
Being able to say you have the bar-none best card out there by leaps and bounds is certainly worth something. Look at all the fanboys that are out there. Every week or month you're able to stay on top of the benches means you get more people who'll swear by your products no matter what for years to come. Everyone you can entice into buying your card who sees it as a good product will buy your brand in the future as a preference, all other options being equal. I could be wrong, but suspect Nvidia's going to make money off this just fine.
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"I am proud that our readership demands a quality above and beyond the norm, and I hope that that never changes. Everything in our power will be done to assure that events like this will not happen again."
See... that's why I'm a big fan of the site.
mlittl3 - Wednesday, June 22, 2005 - link
#78, I bet you didn't even read the article. How do you know it demonstrated editoral integrity?IronChefMoto - Wednesday, June 22, 2005 - link
#23 (mlittl3) still can't pronounce "Penske" and "terran" right, regardless of the great editorial integrity demonstrated by the AT team today. Thanks!