The arrival of PCI Express to the graphics scene has caused quite a stir to the enthusiast community. Here we have a new technology that is destined to replace the long established AGP and PCI. What exactly is PCI Express and what’s so promising about it? Today we’re reviewing the GeForce 6800GT, one of the first PCI-Express video cards.
Well I can bore you with so much techno stuff as to this new PCI Express architecture or I can just sum it up for you. PCI Express equals High bandwidth per pin, Low overhead and Low latency. The old PCI bus worked at 133Mbps with read and write sharing the same bandwidth while a PCI Express X1 provides 250Mbps read and write on a dedicated bandwidth per slot. As for the graphics department, the old AGP bus currently maxes out at 2.1Gbps (8xAGP) while the PCI-E X16 counterpart provides up to 4Gbps of bandwidth. Almost doubling that of the 8xAGP. Not only that, the bandwidth of a PCI Express link may be linearly scaled by adding signal pairs to form multiple lanes. The physical layer supports x1, x2, x4, x8, x12, x16 and x32 lane widths. What this means for graphics card manufacturers is the reality of producing even more powerful cards that can handle more data and smoother graphics. For a more in-depth understanding of the PCI-Express architecture, there’s a mountain of information here.
Intel was the first motherboard manufacturer to integrate PCI Express into their chipsets. The release of their i915/i925x chipsets marked the beginning of this new era in computing. Of course, the major players in the graphics arena wasn’t far behind developing video cards that would make use of this new technology. nVIDIA was particularly very excited about this feature due to a “secret” technology that they themselves developed out of this new bus architecture. Well by now we all know what it is, it’s nVIDIA’s SLI (Scalable Link Interface). This multi-GPU technology takes advantage of the increased bandwidth of the PCI Express bus architecture, and features intelligent hardware and software solutions that allow multiple GPUs to efficiently work together to deliver earth-shattering performance. Neat huh?
Today’s review though is not about nVIDIA’s SLI as there is no retail board that we know of that supports dual PCI-E X16 slots at the moment. We will however give you a feel of the performance that you can expect from one of nVIDIA’s PCI Express cards. That way you can have an idea of the good things to come once SLI is readily available. On our testbed today is nVIDIA’s NV45 chip better known as the GeForce 6800GT 256Mb PCI-E Reference Card. Come and join us as we explore the world of PCI Express.
The nVIDIA GeForce 6800GT
The NV45 is the first PCI Express card that nVIDIA showed off last June of this year at Computex. As we know, the first crop of nVIDIA PCI Express cards feature an external HSI (High Speed Interconnect) chip acting as a bridge between the PCI Express bus and the gpu. We won’t go into the details regarding the advantages and disadvantages of using such approach as argued by both sides. What we will do is find out the actual performance this card can deliver to the end user.
Clocked at 350MHz core and 1000MHz memory, the NVIDIA 6800GT is just a clocked down version of the flagship GeForce 6800 Ultra/Extreme. There is really no other difference architecture wise except that it’s a PCI-E card rather than AGP. It too has the same 16 pixel pipelines that is lacking from the “crippled” GeForce 6800 which only has 12 pixel pipelines. It also uses 256MB of GDDR3 across a 256-bit bus which is what the Ultra/Extreme version has. Overclock this card and you’ll end up with an 6800 Ultra/Extreme PCI Express card in your hands. Below is a table comparing the GeForce 6800GT PCI-E to the current crop of graphics cards.
NVIDIA 6800GT Design
The GeForce 6800GT PCI-E Reference card is exactly the same length as the Reference 6800 Ultra version. The difference in size is quite evident as the 6800 Ultra boasts a much bigger HSF that occupies 2 slots in an AGP based system. Being a PCI Express card, the connector is of course different to the AGP part.
The cooling solution used is one might call average for the core and above average for the memory. The core is actively cooled by a low profile aluminum heatsink and a centrifugal impeller that blows air directly to the core and memory’s ramsinks. This heatsink is held in place to the gpu by an X-type aluminum bracket located at the back of the card. Thermal compound can be found between the heatsink and the gpu while thermal pad was used as interface between the memory chips and the RAM sinks.
The GeForce 6800GT PCI-E Reference card uses 256mb of Samsung GDDR3 FBGA chips, part no. K4J55323QF-GC20. Rated at 2.0ns, its maximum theoretical speed is 1000MHz DDR. That means that these modules are already running at their maximum. This leaves no headroom for overclocking. We’ll see whether the above average ramsinks will help push the memory beyond its rated speed. As for the GPU, here we can see the engineering sample NV45 chip being used. Notice the HSI (High Speed Interconnect) just below the core. This is the much talked about “AGP-to-PEG bridge” that transforms nVIDIA’s GPUs into PCI Express GPUs.
Like its AGP counterpart, the 6800 GT PCI Express needs extra power via an external power connector. The difference though is that it doesn’t use the familiar molex power connector we are accustomed to. Instead, it uses a new 6-pin power connector straight from the power supply (scarcely available to newer models) or via an adapter for use with older PSUs. The adapter gets it power from 2 molex connections. In other words, this 6-pin power connector is equivalent to the 2 x molex connectors found in 6800Ultra AGP cards. I am pretty sure that retail 6800GT PCI-E cards would come with this adapter so as to avoid the unnecessary upgrading of power supplies just to run this card. Note that a heatsink is also placed on top of the resistors for power stability.
The 6800 GT card is equipped with dual DVI connectors for digital flat panel displays and no VGA connector for analog CRT. I suppose you can use an adapter if you plan of using CRT monitor for this card. Again, I’m sure retail units will come with one or even two included in the package.
SLI (Scalable Link Interface) anyone? At the moment, there are only 3 nVIDIA PCI Express cards that can support this technology. The GeForce 6800GT PCI-E is one of them. The other two are the GeForce 6800 Ultra PCI-E and 6600GT PCI-E card. With this technology, you can combine two GeForce 6800GT PCI-E cards or the like to take full advantage of the increased bandwidth of the PCI Express bus architecture- that’s up to 8Gb/s of raw graphics performance. This multi GPU approach will definitely change the way we play games. It might be expensive but of course, the ultimate performance freak with money to burn wouldn’t mind. Saying that though, two 6600GTs in SLI won’t be that expensive. Of course we have to wait for motherboards that will feature dual PCI-E X16 slots before the end user can take advantage of this technology. I tell you though, it won’t be a long wait. This is something that I’m sure a lot of people are looking forward to.
Overclocking the GeForce 6800GT
People buying this card is obviously expecting to hit “Ultra” speeds via overclocking. Getting it to run at that speed would definitely make the purchase a bargain. As we said the only difference between a GT and the Ultra is their corresponding clocks. If one can get the 6800GT to run stable at Ultra speeds, then the performance would be the same but the price would a hell lot cheaper. However based on the information we have with regards to the memory’s theoretical speed, this card is already running at its max memory wise. But of course, we won’t know till we try. So the question is, how far did this reference 6800GT PCI-E go? Using coolbits, the maximum rock solid overclock we got the card to work without crashing and artifacts is 415MHz on the core and 1120 on the memory. That’s more than the 6800Ultra speeds. That’s almost a 15% overclock on the core and 12% on the memory. Quite impressive considering the little headroom we have on the memory.
Testing and Performance
Testing was done by benchmarking the nVIDIA reference 6800GT PCI-E card using some of the most famous and latest games. This card was tested using an i915P board and DDR2 setup. The 6800GT PCI-E’s performance was then compared to its 6800GT AGP counterpart and to the current top AGP cards as well. These cards include the GeForce 6800Ultra and the Radeon X800XT. We’ll also include the test results generated by the overclocked 6800GT PCI-E card.
All tests were done using the latest official drivers from ATI and NVIDIA at the time of testing. Stock tests were done using “No AA No AF” settings for all cards. IQ tests were done with Anti-Aliasing set at 4x and Anisotropic Filtering at 16x via each card’s control panel. All cards were tested using their default speeds.
Conclusion of the GeForce 6800 GT
nVIDIA’s Reference GeForce 6800GT PCI Express card has showed some excellent numbers on our tests. Its performance would definitely not disappoint even the most serious of gamers. It is able to play all of the latest games without any problems and with ease even with Image Quality set on high. IQ tests still managed to give very impressive numbers.
When compared to its NVIDIA 6800GT AGP counterpart, it showed little or no difference at all even though they are running on different chipsets. At the moment, the performance advantage of having a PCI-E card matched with DDR2 is not yet realized. Although we can see the PCI-E card ahead at times against the AGP 6800GT, most of the times they both give the same results. Future games though would obviously take advantage of the huge bandwidth that these systems can deliver.
Although the 6800 GT is not aimed at the 6800Ultra and X800XT markets, we can see that it gives both cards a run for their money. There are even times that we can see the 6800GT edging out the X800XT in some games. What more against its ATI counterpart, the X800Pro? From the looks of it, the 6800GT is obviously the more appealing choice between the two in terms of performance. Having almost the same price tag, the choice get’s even easier.
Overclocked, the GeForce 6800 GT performance just tops almost all the competition. This is why this card has a big future ahead of itself. The ability to run over 6800Ultra speeds will be the number one attraction for the 6800GTs be it in PCI-E or AGP form. Pricewise, this card is currently about US$100-200 cheaper than both ATI and nVIDIA flagship cards. Now that’s a lot of money in terms of future upgrade options. This alone would be the biggest selling point of this card.
As for the PCI-Express technology, even though we have seen very little difference when compared to AGP parts, I would definitely recommended PCI-E now to serious gamers who are on the upgrade path anyway. I don’t see any reason why you have to buy old technology when you have a newer technology in front of you that promises so much more. I have to say though that if you’re only planning of upgrading the graphics card and not the whole system, then you’re better of with an AGP. One thing that can be said about the getting a 6800GT PCI-E is that it will futureproof your investment. And with SLI just peeping at the corner, it is more than enough reason for you to get this card. That is if SLI is playing in your mind. I know mine is.
With all that said, the 6800 GT PCI-E is not for everyone. Mainstream and casual gamers need not apply. This card is for the serious and the extreme gamer out there. Bottomline, gaming experience with this card is currently one of the best dollar for dollar.