Intel did a very good job of drumming up support for PCI Express over the past two years.  Look around and note that all of the motherboard manufacturers have quite a few PCI Express based motherboard designs.  Then look at the latest GPU launches from ATI and NVIDIA, all of the exciting products appear to be launched first (or primarily) as PCI Express designs.  While everyone industry-wide has done a great job of supporting PCI Express, there's one little problem - no one seems to be interested in buying PCI Express solutions just yet. 

The OEM markets have no problems shipping PCI Express motherboards and graphics cards in their systems, after all they want to sell the idea of buying an entirely new PC in order to get access to brand new technologies like PCI Express.  However in the channel and upgrade markets, PCI Express solutions aren't selling well at all.  Most enthusiast users appear to be sticking with their AGP platforms and while they would consider a GPU upgrade, they are not willing to upgrade their motherboard (and sometimes CPU and memory) just to get a faster graphics card. 

There was a huge debate early on about whose PCI Express design would prove to be the best for performance.  ATI chose to produce separate PCI Express and AGP enabled GPUs, offering a native solution for both interfaces; meanwhile, NVIDIA chose to keep manufacturing their AGP GPUs and use a bridge chip to interface with PCI Express.  While ATI argued that NVIDIA's solution offered less performance, NVIDIA said that ATI's approach was far too costly.  The problem with ATI's approach was that their production was inherently split between AGP and PCI Express chips, and predicting market demands for an appropriate ratio between the chips is quite difficult.  If you overproduce PCI Express chips, then there will be a shortage of AGP cards, and vice versa.  ATI's initial approach to only producing native PCI Express or AGP designs is part of the reason why their latest mainstream GPUs (e.g. X700) are still only available as PCI Express designs.

Even though NVIDIA has gone to manufacturing native PCI Express GPUs (e.g. GeForce 6600GT), they already have a working chip to bridge back down to an AGP interface, which is what makes today's launch possible.  Thanks to the use of NVIDIA's PCI Express-to-AGP bridge chip, NVIDIA is able to not only launch but also begin selling an AGP version of their GeForce 6600GT today.  We are told by NVIDIA that cards should be available for sale today continuing a very recent trend of announcing availability alongside a product launch, which we greatly applaud. 


NVIDIA's PCI Express to AGP bridge

ATI is working on a PCI Express-to-AGP bridge of their own, but it will not be ready until later this year - meaning that ATI will not have an AGP version of their PCI Express X700 until early next year.

The GeForce 6600GT AGP runs at the same core clock speed as the PCI Express version (500MHz) but has a slightly lower memory clock (900MHz vs. 1GHz on the PCI Express version).  By lowering the memory clock NVIDIA helps to offset the additional cost of the PCI Express-to-AGP bridge.  The performance impact of the reduction in memory clock as well as the on-board bridge is between 0 - 5%.  For example, in Doom 3 at 1024 x 768 (High Quality) the PCI Express version of the GeForce 6600GT is 3.5% faster than the AGP version.  There is a performance difference, but it does not appear to be huge. The AGP version of the 6600GT obviously lacks SLI support given that you can only have a single AGP slot on a motherboard.

The latest AGP specification calls for a maximum of around 45W of power to be delivered via the AGP slot itself, while a PCI Express x16 slot can supply up to 75W.  Because of the reduction in power that can be delivered via the slot interface, the GeForce 6600GT AGP requires the use of a 4-pin molex connector on the board itself to deliver extra power to the GPU.  You may remember that the PCI Express version of the 6600GT does not require a separate power connector. 


This 4-pin molex connector is only present on the AGP version of the 6600GT

As of now, NVIDIA is only releasing the 6600GT in an AGP flavor; the regular non-GT 6600 will remain PCI Express only. the 6600GT AGP will retail for between $200 and $250. If you are interested in learning more about the architecture of the 6600GT, feel free to read our review of the PCI Express version for greater detail.

The Cards
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  • Pythias - Wednesday, November 17, 2004 - link

    >>The impact of the bridge, as I mentioned in the review, is negligible. The bridge + slower memory results in a 0 - 5% performance difference between the PCI Express and AGP versions of the 6600GT (the 5% figure being because of the additional memory bandwidth courtesy of the 500/1000 clock vs. 500/900).

    Just so you guys know, I went out and picked up a vanilla 6800 for inclusion in my upcoming Half Life 2 GPU comparison. Know that your voice has been heard :)

    Take care,
    Anand<<<

    Anand, you kick teh bootay.
    Reply
  • Poser - Tuesday, November 16, 2004 - link

    #42 He's not benching them with the fastest processor he can get his hands on just to show off what cool hardware he's got, you know. If you match up a fast video card with a slower processor, you can get benchmark scores that are CPU limited, instead of GPU limited like you want to see. You can see a little bit of what CPU limiting looks like when you look at the low resolution benchmarks with older games, and even with Unreal Tournament 2004 in this review. Every card ends up with essentially the same score, because it's no longer the video card that's the bottleneck -- it's the rest of the system, chiefly the CPU.

    If you knew all that already, my apologies for the mini-lecture =). I agree that it's nice to occassionally see benchmarks with a range of processors so that you can spot "yours" and see what sort of performance boost you'd get by upgrading, but it hardly seems practical to do that for every video card review and if you've got to pick ONE processor to test everything on, then the fastest available is a good choice.
    Reply
  • thebluesgnr - Tuesday, November 16, 2004 - link

    #41,
    the PT894 Pro chipset should be sampling right now.

    Reply
  • bhtooefr - Tuesday, November 16, 2004 - link

    draazeejs: Anand compared it against other cards that are the same price. So, a 2 year old card that is now that same price IS a fair comparison. Reply
  • Niatross - Tuesday, November 16, 2004 - link

    I know you've heard this comment a million times before. I don't have a FX 55 I've got an Athlon 2500 mobile. These benchs mean absolutly nothing to me Reply
  • Tanclearas - Tuesday, November 16, 2004 - link

    "Most enthusiast users appear to be sticking with their AGP platforms and while they would consider a GPU upgrade, they are not willing to upgrade their motherboard (and sometimes CPU and memory) just to get a faster graphics card."

    Don't you think this has something to do with the fact that you still can't purchase AMD PCIe boards? Not to mention that it looks like the only (realistic) SLI solution that will be available in the next several months will be for Athlon 64.
    Reply
  • Pete - Tuesday, November 16, 2004 - link

    #28, as ATi won't be releasing the X700XT in AGP form for quite some time, and as they're actually going to (continue to) use the 9800P as competition at the $200 price point, your accusation is wholly without merit. If you want to see X700XT vs. 6600GT numbers, just read Anand's X700XT review. As it stands, the 6600GT is unchallenged in the field of new AGP cards at $200.

    But it's way overpriced for the $250 NewEgg is charging for it, dual DVI or not. For $250, you're better off with the BFG 6800OC at Outpost.com (which may even come with Far Cry, making it an even better deal).
    Reply
  • coldpower27 - Tuesday, November 16, 2004 - link

    The review at firingsquad also seems to paint the same pciture, the conclusion there is similar in wording to the conclusion here to me. It seems the 6600 GT AGP is most definitely a good video card for the mass market :P Reply
  • ChronoReverse - Tuesday, November 16, 2004 - link

    To #28

    A quote from HardOCP

    "One thing is for sure, the GeForce 6600GT and the Radeon X700XT are very competitive products when it comes to overall gaming performance. If we had to edge out a card that offers up the better value we would have to lean towards the GeForce 6600GT at this point in time. In our two days of X700XT experience we saw it get held out of the top spot in terms of both framerate and image quality by the GeForce 6600GT. Keep in mind that the GeForce 6600 series also packs the performance potential of Shader Model 3.0 once games start using it."

    Any nVidia bias you attribute to Anandtech is unfounded.
    Reply
  • vailr - Tuesday, November 16, 2004 - link

    Some AVSForum.com (/Home Theater Computers) postings had said that the 6600 video processor was fine; that only the 6800 (the AGP version specifically) had certain hardware problems, which "cannot be cured by a driver update". Or, that maybe some future Windows Media Player update would be needed, to enable hardware assisted .wmv files.
    So, general confusion, as to what the real facts are.
    "nVidia admits 6800 has faulty on chip decoder":
    http://www.avsforum.com/avs-vb/showthread.php?s=&a...
    Reply

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