Asus N7800GT DUAL Review – 7800 SLI on a Single Card

Included Extras, Motherboard Compatibility and Test Setup

Like most graphics card vendors, Asus has been struggling with the idea of including extras in the box with their cards.  What do users want and what will make a user choose their card over a competitor’s?  Well, the Asus N7800GT DUAL won’t really have the problem but Asus still has a decent mix inside the box.

The most exciting information (though not included in MY box, damnit!) was that Asus is going to start bundling Call of Duty 2 in with the N7800GT DUAL starting on 10/25, when the game is released to the world.  A $50 game that most enthusiasts will probably end up picking up makes the price of the card a bit more appealing, no matter the cost.

Other than that, Asus has included their normal mixture of parts including two DVI-to-VGA adaptors, a power adaptor, a video output dongle that supports HDTV, and an Asus SLI paddle for Asus’ own Intel-based SLI boards needed to support this video card.  The software mix includes SnowBlind and some other applications for watching and creating DVDs and digital content. 

Motherboard Compatibility

This is something of an issue with this card, and has been since Gigabyte released their first dual-GPU video card a while back.  In fact, Gigabyte went as far as to bundle that 3D1 video card with their own motherboard as it was the only supported combination at first. 

The Asus N7800GT DUAL officially supports six motherboards at this time: Asus P5ND2-SLI and Deluxe, Asus A8N-SLI, Deluxe and Premium and the Gigabyte K8NXP-SLI. 

The reasons behind the compatibility issues are still not perfectly clear to me, though I do know it has to do with the motherboard manufacturers implementation of the SLI paddle switch responsible for setting either x16 or x8 PCIe lanes to a PCI Express slot. 

Your best bet might be to wait until someone tests your particular motherboard with the card to see if it functions, or to continually check out Asus’ website for updates, though I wouldn’t place my hopes on super-timely updates. 

Update (10/13/05 @ 1:10pm EST):

Here is the latest list of supported motherboards from Asus as of today:

• Asus P5ND2-SLI
• Asus P5ND2-SLI Deluxe
• Asus P5N32-SLI (needs new BIOS)
• Asus A8N-SLI
• Asus A8N-SLI Deluxe
• Asus A8N-SLI Premium
• Asus A8N32-SLI Deluxe
• DFI nF4 SLI-DR
• Gigabyte GA-K8NXP-SLI

The reason behind the seemingly random compatibility issue is in fact the implementation of the PCI Express paddle card that most SLI motherboard utilize to switch between x8 and x16 lanes of PCI Express.  Asus is saying not that this video card should work on most AMD-based SLI motherboards from other vendors, but that the Intel-based SLI chipset uses a different method to support SLI so most C19 motherboards will not support it.  It depends greatly on the implementation of the vendors switch card. 

Update (10/13/05 @ 1:20pm EST):

Even more detailed information on the issue at hand. 

This is a standard PCI Express graphics card connection diagram.  All x16 cards are setup so that lane 0 of the PCI Express bus (going from 0 to 15) starts at the left hand side of the and continues across to the right up to the 15th lane.  For SLI to function on a motherboard, the paddle card between the two PCI Express slots has to take a physical x16 connection and split it up between two slots, giving each 8 lanes of PCI Express bandwidth. 

On the CK804-based A8N-SLI motherboard, when in single card mode, all 16 lanes are going to the primary (north) slot on the motherboard.  When the card is changed to SLI mode, the lanes are divided up into x8 lanes for the north slot in the form of connections 0-7 and x8 lanes to the south slot with connections 8-15.  However, the C19-based P5ND2 motherboard from Asus divides those 16 lanes up different, giving connections 0, 2, 4, 6, 8, 10, 12 and 14 to the north slot and 1, 3, 5, 7, 9, 11, 13, and 15 to the south slot. 

What does that mean in relation to the Asus N7800GT DUAL?

This is a diagram of the PCIe connections on the N7800GT DUAL card.  The lines going up from the left half of the connection go to GPU1 and the traces heading off in the right direction go to GPU2.  PCIe connections 0-7 go to the first GPU and connections 8-15 go the second GPU.  Since we know that the AMD-based A8N-SLI divides the PCIe lanes up identically with the switch board, the video card has no problems working with that configuraiton.  However, the Intel-based P5ND2-SLI alternates between connection lanes to the north and south bridge, and therefor the N7800GT DUAL can not make the connections properly. 

Asus has included a new paddle board that corrects the issue on their P5ND2-SLI series of motherboards but they claim that the card is not compatible with competitors motherboards. 

Now, if we can get the details of how each SLI motherboard implemented their SLI paddle card we can know for sure whether or not it is going to function with this Asus graphics card.

Testing Methodology

Graphics card testing has become the most hotly debated issue in the hardware enthusiast community recently.  Because of that, testing graphics cards has become a much more complicated process than it once was.  Where before you might have been able to rely on the output of a few synthetic, automatic benchmarks to make your video card purchase, that is just no longer the case.  Video cards now cost up to $500 and we want to make sure that we are giving the reader as much information as we can to aid you in your purchasing decision.  We know we can’t run every game or find every bug and error, but we try to do what we can to aid you, our reader, and the community as a whole.

With that in mind, all the benchmarks that you will see in this review are from games that we bought off the shelves just like you.  Of these games, there are two different styles of benchmarks that need to be described.

The first is the “timedemo-style” of benchmark.  Many of you may be familiar with this style from games like Quake III; a “demo” is recorded in the game and a set number of frames are saved in a file for playback.  When playing back the demo, the game engine then renders the frames as quickly as possible, which is why you will often see the “timedemo-style” of benchmarks playing back the game much more quickly than you would ever play the game.  In our benchmarks, the FarCry tests were done in this matter: we recorded four custom demos and then played them back on each card at each different resolution and quality setting.  Why does this matter?  Because in these tests where timedemos are used, the line graphs that show the frame rate at each second, each card may not end at the same time precisly because one card is able to play it back faster than the other — less time passes and thus the FRAPs application gets slightly fewer frame rates to plot.  However, the peaks and valleys and overall performance of each card is still maintained and we can make a judged comparison of the frame rates and performance.

The second type of benchmark you’ll see in this article are manual run throughs of a portion of a game.  This is where we sit at the game with a mouse in one hand, a keyboard under the other, and play the game to get a benchmark score.  This benchmark method makes the graphs and data easy to read, but adds another level of difficulty to the reviewer — making the manual run throughs repeatable and accurate.  I think we’ve accomplished this by choosing a section of each game that provides us with a clear cut path. We take three readings of each card and setting, average the scores, and present those to you.  While this means the benchmarks are not exact to the most minute detail, they are damn close and practicing with this method for many days has made it clear to me that while this method is time consuming, it is definitely a viable option for games without timedemo support.

The second graph is a bar graph that tells you the average framerate, the maximum framerate, and the minimum framerate.  The minimum and average are important numbers here as we want the minimum to be high enough to not affect our gaming experience.  While it will be the decision of each individual gamer what is the lowest they will allow, comparing the Min FPS to the line graph and seeing how often this minimum occurs, should give you a good idea of what your gaming experience will be like with this game, and that video card on that resolution.

Our tests are completely based around the second type of benchmark method mentioned above — the manual run through.

Test System Setup

Each set includes a line graph and a bar graph.  The line graph still shows the performance over the span of time of the benchmark and the bar graph shows the data in a min/max/avg format that many readers like to see and are more comfortable with. 

Software tested:

• Doom 3 v1.3
• Far Cry v1.3
• Half-Life 2 Engine 7 (two maps)
• EverQuest 2
• Battlefield 2
• Guild Wars
• FEAR SP Demo
• 3DMark05

Drivers

I have already been asked whether or not this card requires special drivers from Asus in order to work correctly.  The answer is no, as we used the standard 77.77 reference drivers from NVIDIA’s website for this review.  In Windows, the N7800GT DUAL actually shows up as two separate devices, each a 7800 GT card.  The NVIDIA drivers install as normal and you can enable and disable SLI just as you would normally.  All the driver features are available and usable.