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.

No More Memory Bandwidth No More Shader Replacement


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  • multiblitz - Sunday, June 26, 2005 - link

    It would be great of you could do a comparison between the 6800 and the 7800 in video /DVD-playback-quality similar to the comparison betwenn the X800 and the 6800 you did last year. Reply
  • at80eighty - Saturday, June 25, 2005 - link

    OMG! I've never seen so many bitching whiners come outta the woodworks like this!!

    You A-holes oughta remember that this site has been kept free


    The editors owe YOU nothing. At all.

    AT team - accidents happen. Keep up the great work!

    /#121 : well said. Amazing how these turds dont realise that the knife cuts both ways...
  • mrdeez - Friday, June 24, 2005 - link

    You can stfu too...j/k..point taken .

    I guess the real issue for me is that this card is a beast but ill never have it in my sli rig......i want all settings maxed at playable resolutions thats just me.........and i will not go back to crt thats was lame dude
  • Momental - Friday, June 24, 2005 - link

    #122 The problem with your solution regarding "all of us just getting two 6880U's" works perfectly for those with an SLI-capable board, yes? Some of us, like myself, anticpated the next generation of GPU's like the 7800 series and opted to simply upgrade to one of those when the dust settled and prices slid back a bit.

    Additionally, telling someone to "STFU" isn't necessary. We can't hold a conversation if we're all silent. Knowhuddamean, jellybean? Hand gestures don't work well over the internet, but here's one for you..........
  • SDA - Friday, June 24, 2005 - link

    LCD gamers shouldn't be bothering with new graphics cards, they should get new monitors.

    kidding, I have nothing against LCDs. The real advantage of showing the card run at 2048x1536 is that it lets you see how well the card scales to more stressful scenarios. A card that suddenly gets swamped at higher resolutions will probably not fare well in future games that need more memory bandwidth.

    On a side note, you can get a CRT that will run 2048x1536 @ a reasonable refresh for about $200 shipped (any Sony G520 variant, such as the Dell P1130). The only things that would actually be small in games are the 2D objects that have set pixel sizes, everything else looks beautiful.
  • mrdeez - Friday, June 24, 2005 - link

    lol ty for your insight....anyway like i said this card is not for lcd gamers as most have a 12x10 or what purpose does this card have??answer me this batman and you have the group that should buy this card -otherwise, the rest of us should just get 2 6800u....this card is geared more for workstation graphics not gaming.....unless you game on a hi def crt and even then max res would be 1920 by 1080i..or something like that.....
  • SDA - Friday, June 24, 2005 - link

    #116, if people in the comments thread are allowed to give their opinions, why shouldn't #114 give his too? Surely even an illiterate like you should realize that arguing that everyone is entitled to his or her own argument means that the person you're arguing with is too.

    #119, some people have different requirements than others. Some just want no visible blur, others want the best contrast ratio and color reproduction they can get.
  • bob661 - Thursday, June 23, 2005 - link

    Oh yeah. The monitor goes up to 16x12.
  • bob661 - Thursday, June 23, 2005 - link

    I play BF2 on a Viewsonic VP201b (20.1") at work and it's very good. No streaking or ghosting. Video card is a 6800GT. I play at 1280x960.
  • Icehawk - Thursday, June 23, 2005 - link

    Well, I for one think 1280x1024 is pretty valid as that is what a 19" LCD can do. I'd just want to see a maxed out 12x10 chart to see how it does - I know a 6800 can't do it for every game with full AA and AF. Otherwise I agree - a 12x10 with no options isn't going to show much with current games.

    See, I'm considering swapping my two 21" CRTs for two 19" LCDs - and they won't do more than 12x10. I'd love to do two 20-21" LCDs but the cost is too high and fast panels aren't to be found. 19" is the sweet spot right now IMO - perhaps I'm wrong?

    Thanks AT for a nice article - accidents happen.

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