NVIDIA's GeForce 7800 GTX Hits The Ground Running
by Derek Wilson on June 22, 2005 9:00 AM EST- Posted in
- GPUs
Inside The Pipes
The pixel pipe is made up of two vector units and a texture unit that all operate together to facilitate effective shader program execution. There are a couple mini-ALUs in each shader pipeline that allow operations such as a free fp16 normalize and other specialized features that relate to and assist the two main ALUs.
Even though this block diagram looks slightly different from ones shown during the 6800 launch, NVIDIA has informed us that these mini-ALUs were also present in NV4x hardware. There was much talk when the 6800 launched about the distinct functionality each of the main shader ALUs had. In NV4x, only one ALU had the ability to perform a single clock MADD (multiply-add). Similarly, only one ALU assisted in texture address operations for the texture unit. Simply having these two distinct ALUs (regardless of their functionality difference) is what was able to push the NV4x so much faster than the NV3x architecture.
In their ongoing research into commonly used shaders (and likely much of their work with shader replacement), NVIDIA discovered that a very high percentage of shader instructions were MADDs. Multiply-add is extremely common in 3D mathematics as linear algebra, matrix manipulation, and vector calculus are a huge part of graphics. G70 implements MADD on both main Shader ALUs. Taking into account the 50% increase in shader pipelines and each pipe's ability to compute twice as many MADD operations per clock, the G70 has the theoretical ability to triple MADD performance over the NV4x architecture (on a clock for clock basis).
Of course, we pressed the development team to tell us if both Shader ALUs featured identical functionality. The answer is that they do not. Other than knowing that only one ALU is responsible for assisting the texture hardware, we were unable to extract a detailed answer about how similar the ALUs are. Suffice it to say that they still don't share all features, but that NVIDIA certainly feels that the current setup will allow G70 to extract twice the shader performance for a single fragment over NV4x (depending on the shader of course). We have also learned that the penalty for branching in the pixel shaders is much less than in previous hardware. This may or may not mean that the pipelines are less dependent on following the exact same instruction path, but we really don't have the ability to determine what is going on at that level.
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VIAN - Wednesday, June 22, 2005 - link
"NVIDIA sees texture bandwidth as outweighing color and z bandwidth in the not too distant future." That was a quote from the article after saying that Nvidia was focusing less on Memory Bandwidth.Do these two statements not match or is there something I'm not aware of.
obeseotron - Wednesday, June 22, 2005 - link
These benchmarks are pretty clearly rushed out and wrong, or at least improperly attributed to the wrong hardware. SLI 6800 show up faster than SLI 7800's in many benchmarks, in some cases much more than doubling single 6800 scores. I understand NDAs suck with the limited amount of time to produce a review, but I'd rather it have not been posted until the afternoon than ignore the benchmarks section.IronChefMoto - Wednesday, June 22, 2005 - link
#28 -- Mlittl3 can't pronounce Penske or terran properly, and he's giving out grammar advice? Sad. ;)SDA - Wednesday, June 22, 2005 - link
QUESTIONOkay, allcaps=obnoxious. But I do have a question. How was system power consumption measured? That is, was the draw of the computer at the wall measured, or was the draw on the PSU measured? In other words, did you measure how much power the PSU drew from the wall or how much power the components drew from the PSU?
Aikouka - Wednesday, June 22, 2005 - link
Wow, I'm simply amazed. I said to someone as soon as I saw this "Wow, now I feel bad that I just bought a 6800GT ... but at least they won't be available for 1 or 2 months." Then I look and see that retailers already have them! I was shocked to say the least.RyDogg1 - Wednesday, June 22, 2005 - link
But my question was "who," was buying them. I'm a hardware goon as much as the next guy, but everyone knows that in 6-12 months, the next gen is out and price is lower on these. I mean the benches are presenting comparisons with cards that according to the article are close to a year old. Obviously some sucker lays down the cash because the "premium," price is way too high for a common consumer.Maybe this one of the factors that will lead to the Xbox360/PS3 becoming the new gaming standard as opposed to the Video Card market pushing the envelope.
geekfool - Wednesday, June 22, 2005 - link
What no Crossfire benchies? I guess they didn't wany Nvidia to loose on their big launch day.Lonyo - Wednesday, June 22, 2005 - link
The initial 6800U's cost lots because of price gouging.They were in very limited supply, so people hiked up the prices.
The MSRP of these cards is $600, and they are available.
MSRP of the 6800U's was $500, the sellers then inflated prices.
Lifted - Wednesday, June 22, 2005 - link
#24: In the Wolfenstein graph they obviously reversed the 7800 GTX SLI with the Radeon.They only reveresed a couple of labels here and there, chill out. It's still VERY OBVIOUS which card is which just by looking at the performance!
WAKE UP SLEEPY HEADS.
mlittl3 - Wednesday, June 22, 2005 - link
Derek,I know this article must have been rushed out but it needs EXTREME proofreading. As many have said in the other comments above, the results need to be carefully gone over to get the right numbers in the right place.
There is no way that the ATI card can go from just under 75 fps at 1600x1200 to over 100 fps at 2048x1535 in Enemy Territory.
Also, the Final Words heading is part of the paragraph text instead of a bold heading above it.
There are other grammatical errors too but those aren't as important as the erroneous data. Plus, a little analysis of each of the benchmark results for each game would be nice but not necessary.
Please go over each graph and make sure the numbers are right.