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XFXNvidia's SLI (Scalable Link Interface) has been around for sometime now but up until recently SLI meant linking just two graphics cards together. Not anymore. The white coats at NVidia have been hard at work creating a flagship gaming platform enabling not two but FOUR GPU's in the form of the mighty 9800GX2 x 2. These dual-GPU cards are advertised as the pinnacle of graphics processing technology. What's that you say? Quad SLI aint new! Well OK, Quad SLI started out in life in the form of the 7950GX2 released in mid 2006 but ultimately it fell flat on its face due to scalability problems and Nvidia fell short of delivering better support due to the diminished uptake in the new technology. While the 7950GX2 worked on its own (SLI in a dual PCB - single card solution), Quad SLI performance was ultimately dismal. While I don't agree with the way Nvidia abandoned those stuck with the cards I can understand why they did it as with a new operating system and DirectX10 on the horizon, Nvidia had bigger fish to fry.

3870x2 vs 9800GX2 - CrossfireX vs SLILuckily, the green side of the GPU market have forgiven Nvidia for their past behaviour and have been rewarded with some stunning GPU releases, namely the 8800 GTX. It's been a long time since we had such a fantastic, long lasting, king of performance. Not since the ATI 9700 days has there been a single card dominating the performance sector and despite their best efforts, ATI just could not compete on the same level as Nvidia. You would be forgiven then for believing Nvidia were resting on their laurels as it had been over a year before we saw a 'new' king of the hill. So what pushed Nvidia out of hibernation? CrossFireX. ATI's answer to grabbing back the performance crown. ATI GPU's simply did not have the raw power to dethrone the mighty G80, so instead ATI took a different approach and simply stuck 2 GPU's on the same card in the form of the 3870x2. Now the 3870 is no slouch so linking two of them together on the SAME PCB, with the further possibility of using 4 of the cards in CrossFireX was sure to ruffle a few feathers over at the Nvdia house and kick them into action.
So here we are today with the 9800GX2, Nvidia's flagship card(s). I say cards as although the GX2 is a single slot PCIe solution it is still two PCB's linked together rather than adapting to the ATI approach of putting both GPU's on a single PCB. This time however, Nvidia have wrapped them up in a sleek looking metal frame and rather than looking like the Star destroyer that was the 7950GX2, the 9800GX2 looks strikingly like the Monolith from "A Space Odyssey".

To evaluate the performance of Quad SLI we will be pitching the offerings from XFX against its arch rival the 3870X2 in Quad Fire (CrossfireX) which again is 4 GPU's linked together in a 2+2 format hence comparisons will be made throughout this review in an attempt to discover which solution is best for you.

Lets take a look at the GX2 in greater depth...

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Quad SLI - How it works
Briefly, SLI (Scalable Link Interface) works by combining 2 graphics cards together to render images quicker or indeed with higher settings such as AA/AF. It does this by using one of two methods:
Split Frame Rendering - A process by which each card 'draws' a half of each frame so that every frame you see on the screen is actually processed by both GPU's.
Alternate Frame Rendering - Does exactly what it says on the tin. Each GPU processes a single frame allowing the frames to then be rendered ahead of time preventing any bottleneck of processes waiting to be rendered. This process is called interleaving. One GPU will process one frame while another GPU will process the next, taking it in turns to render the frames.
Quad SLI however first encountered problems with the old 7950GX2 because DirectX 9 was incompatible with 4-way AFR so a mixture of both SFR and AFR was used. SFR is much less efficient than AFR in the latest games due to the amount of complex textures, lighting, ray tracing which is now incorporated in todays modern games era. Due to this and DX9 incompatabilities, the 7950GX2 simply didn't work too well. With DirectX10 now upon us, 4-Way AFR is now not only feasable but with the optimised drivers from Nvidia becomes a very viable solution to those wanting to game at high resolutions with all the trimmings.
4-way AFR
As we will be testing a top of the range setup it should come as no surprise that you will need the best equipment if you are going to take maximum advantage out of the QUAD SLI experience. Here is what I would recommend:

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XFX 9800GX2
When the 8800GTX was released everyone was in awe at the sheer size of it. Well make no mistake the GX2 more than matches the dimensions of its stablemate. With a gloss black powdercoated finish to a metal outer casing and plush stickers that for once add to the appearence of the card than make it look tacky, the XFX 9800GX2 is certainly imposing. Its looks and size are also matched by its weight and this card will certainly add a few pounds to any PC you care to build.
9800GX2 9800GX2
9800GX2 9800gx2
As mentioned previously the 9800GX2 is a dual slot card with two PCB's sandwiched together to make a single card solution. I'm sure this will be debated as to whether this should indeed be classed as a single card, especially by those who enjoy benchmarking but for arguements sake I will be classing each card as just that - a single card.
Above left we see the card with the shroud removed. The shroud itself is a very sturdy affair protecting the internals of the GX2 from all sides and with only the golden fingers of the SLI and PCIe tabs protruding. Static shock damage should be prevented as long as you keep your pinkies away from the said areas. Above right we see the rear of the lower card which unsurpisingly is identical to the top pcb.
Connecting both PCB's is a small bridging SLI ribbon cable. Cooling this monster of a card is a large fan that fills the PCB sandwich and pulls air through both the top and bottom PCB's, pushing the cool air over a copper heatsink that is connected to both GPU's. The hot air is then ejected both from the back and side of the card through the shroud.
With most high-end hardware these days, a powerful PSU is going to be required. Above left we see that both 8-pin and 6-pin PCIe cables will be required for each card - a sure sign of the power draw these cards will have. Q-tec should look elsewhere as each board is rated at a max 197W making near 400W for Quad SLI alone. Add to that the power consumption of a 790i board, Quad core processor and the other peripherals and it becomes clear that only the best PSU's should be used as a powerplant for these beasts. Above right we see the 4 DVI ports of the cards as well as HDMI connectors. It should be noted that at the time of writing, SLI is still not compatible with dual displays so if you want these babies to power multiple monitor displays each card will have to operate individually.
Once slotted in the XFX 790i Ultra motherboard the picture becomes complete. I do appreciate it when everything just 'matches'. Call me picky but I despise gaudy colours on hardware and the design of both the 790i and the GX2's in moody black with just the odd splash of 'NVidia green' is right up my street when it comes to hardware design. The whole setup just looks so classy, yet imposing and while holding one of the cards I couldn't help feeling that this is a quality high-end product. The absence of tacky 'cartoony' stickers that adorn so many graphics cards these days coupled with the sleek black shrouds and the weight of the cards gave me a sense of pride and anticipation of things to come....

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I don't normally endeavour to go into the specifics of 'how to' concerning installations but I feel this may be of some use to anyone wishing to go SLI or indeed Quad SLI.
The installation was really very easy. I was actually quite surprised at how simple it was considering the headaches I have had in the past with the 7950 GX2 Quad SLI. I simply installed Windows Vista with one card, installed the relevent updates and chipset drivers and the latest graphics driver from NVidia, when prompted to reboot I did so. Next I shutdown the system, inserted the 2nd 9800GX2, attached the SLI bridge and PCIe cables and booted back up. SLI capability was detected straight away.
Enabling SLI was again straightforward. The Installed Nvidia control panel with the 175.16 driver release from NVidia was a breeze to use and after applying the change from do not use SLI to Enable SLI the screen went blank a few times as the drivers were installed for the second card. I should note that when the first driver is installed it actually installs the driver twice, once for each GPU and so it seemed the same thing was happening when the second card was installed. So after the snap crackle and pop installation procedure I enabled the SLI visual indicator to check all was well and sure enough Quad SLI was working!
Test setup
As we will be benchmarking a 'top of the range' GPU setup it's only right that the rest of the components should be specced to match. The Q6600 was overclocked to 3.8ghz in order to erradicate any CPU bottlenecks allowing both test rigs to 'breathe more easily' as it were. Unfortunately we didn't have a DDR3 Intel motherboard capable of PCIe 16x and crossfire, however the Crucial ballistix 8500 were overclocked to compensate and with lower timings than DDR3 so the differences would be negligable but this should be taken into consideration when comparing the results of both systems. Other than that the systems are identical to one another and should make for quite a pairing when the two go head-to-head.
As you can see below the cards are very closely matched on paper with the 3870x2 having a higher core clockspeed and the 9800GX2 having a higher memory clockspeed. The 3870x2 is however £80 cheaper at the time of writing so ATI have a clear advantage in the price war.
Lets take a look at how the benchmarks went....

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3DMark® Vantage is the new industry standard PC gaming performance benchmark from Futuremark, newly designed for Windows Vista and DirectX10. It includes two new graphics tests, two new CPU tests, several new feature tests, and support for the latest hardware. 3DMark® Vantage is based on a completely new rendering engine, developed specifically to take full advantage of DirectX10, the new graphics API from Microsoft.
Clearly the brute power of the 9800GX2's have the upperhand here, they also scaled slightly better in Quad SLI. Sadly 3DMark Vantage returned a '0' score for the 2560x1600 run on all cards even though the benchmark ran to its completion each time. This could be down to a number of reasons, driver errors, buffer overflow errors but I suspect its simply a bug in Vantage at this early stage in its development.
3DMark® 06 is a popular synthetic gaming benchmark used by many gamers and overclockers to gauge the performance of their PC's taking advantage of todays multi CPU and GPU performance. All 3DMark runs were performed a total of 5 times with the highest and lowest results being removed and an average calculated from the remaining 3 results.
Here we see the opposite of Vantage with the 3870x2 winning out overall. Scaling here was a mixed bag with the 3870x2's scaling well in both single and dual cards but the GX2 is the better once AA/AF is applied at high resolutions. So its pretty much neck and neck for the artificial benchmarks. Let's move on to some real world gaming conditions....

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Crysis is without doubt one of the most visually stunning and hardware challenging games to date. By using CrysisBench - a tool developed independently of Crysis - we performed a total of 5 timedemo benchmarks using a GPU-Intensive pre-recorded demo. To ensure the most accurate results, the highest and lowest benchmarks scores were then removed and an average calculated from the remaining three.
Clearly the 9800GX2 has slaughtered the 3870x2 in both single and dual card (quad setup). I was amazed at how well the GX2 handled Crysis but also distraught at the hassles involved in trying to get it to work in Quad SLI. For some odd reason on occassions the benchmark would run at a mere 4 or 5 fps on the GX2 and only a reboot or re-install of the drivers would solve this - something you may want to consider should you have the same problems. When it ran Quad SLI though it was truly awsome as the results show. It wasn't even phased by the AA/AF at such a high res and showed very little slowdown once the AA/AF was applied. In contrast the 3870x2's performance was dire. For a high-end setup I expected much more from ATI, With a poor FPS readout at both resolutions. I did a quick run without AA/AF and the fps jumped more inline with the 9800GX2's so clearly the AA/AF settings were crippling the cards.

Bioshock is a recent FPS shooter by 2K games. Based on the UT3 engine it has a large amount of advanced DirectX techniques including excellent water rendering and superb lighting and smoke techniques. All results were recorded using F.R.A.P.S with a total of 5 identical runs through the same area of the game. The highest and lowest results were then removed, with an average being calculated from the remaining 3 results.
A much better showing here from ATI but once more the performance was left wanting in comparison to the 9800GX2. With the Quad fire setup barely beating a single GX2. Therefore it should come as no surprise that the Quad SLI setup once more trounces the CrossfireX. Again I ran a quick test without AA and the ATI did make some ground but if you are spending £500 on a set of GPU's you expect to be able to add AA/AF and at a high resolution. 

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Call of Duty 4 is a stunning DirectX 9.0c based game that really looks awesome and has a very full feature set. With lots of advanced lighting, smoke and water effects, the game has excellent explosions along with fast gameplay. Using the in-built Call Of Duty features, a 10 minute long gameplay demo was recorded and replayed on each of the GPU's using the /timedemo command a total of 5 times. The highest and lowest FPS results were then removed, with an average being calculated from the remaining 3 results.
Very similar results were had with Infinity Ward's first person shooter. While the 3870x2 was smooth to play the Quad SLI rig showed its superiority at both resolutions and once more AA/AF was a factor in the 3870x2's demise....I think we are starting to see a pattern here.

Oblivion from Bethseda is now an 'old' game by today's standards, but is still one of the most visually taxing games out there. The benchmark was run in the wilderness with all settings set to the maximum possible. Bloom was used in preference to HDR. The test was run five times with the average FPS then being deduced.
A much older game showed a closer set of results for all the setups concerned. Despite this, the 9800GX2 is the clear winner here once more.

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The way its meant to be played?
Well I think the results speak for themselves. It's quite clear that a Quad SLI setup will currently demolish any other GPU setup currently on the market. I guess that dosn't come to much of a surprise to many as most are now aware of the current lead Nvidia hold over ATI. What did surprise me is how much better the Quad SLI handled Antialiasing and Anisotropic filtering. While the Quad SLI just shrugged its shoulders, the 3870x2 cringed and cowered when the settings were applied which is a real shame as without the AA and AF settings the 3870x2 CrossfireX setup is a solid performer and can handle anything out there.
However those who want the best and desire maxed out settings with AA and AF need only look toward these results which show the GX2 Quad SLI setup standing triumphantly. Not only is it astounding in Quad SLI but the XFX card is also a very capable single card solution, in fact it can still holds its own against the G200 cards that have recently been released. The G280 might overtake the GX2 with more mature drivers and would also likely outclass it in SLI but with Nvidia's slow release of drivers I wouldn't hold your breath. With this new release, the price of the GX2 is now becoming more affordable to those mere mortals among us; so much so that the bang-per-buck crown the ATI card held is now not so secure.
So is it win/win for Nvidia and specifically XFX?. Well yes and no. Performance-wise there is no doubt the 9800GX2 Quad SLI setup is currently unbeatable, however this can come at a price. Nvidia are still very slow with driver updates and the buggy reponse in Crysis, getting the setup to perform as required almost had me throwing the damn setup out of the window. However as the cards are not mine to keep and fearing a horses head on my pillow should I make off with them, I ventured on and gradually sorted the problems out, something that wasn't required with ATI. Having said that they are a dramatic improvement over the previous Quad SLI setup which Nvidia failed to resolve and despite the numerous rants and head scratching coming from our test labs, I would happily purchase these cards in a heartbeat had I the funds to do so.
So in short ATI still have some catching up to do if they are to dethrone their arch-enemy and if they can sort the AA/AF issues that crippled the CrossfireX setup then I would be very cagey about placing any bets in the near future, especially as rumours are beginning to surface regarding the excellent performance of the 4000 series cards. For now thought the 9800GX2 is the heavyweight champion and it is going to take a very fast card(s) to outperform it.
The XFX 9800GX2's used in today's review can be purchased over at Scan.co.uk for a rather eye watering £325 each.
The Good
- Nothing can currently touch its performance.
- Quad SLI is very easy to setup.
- Looks great.
The Mediocre
- Power requirements.
- The cooling solution dumps heat into the case.
- The price of 2 cards is going to leave little, if any change from £600 although prices are beginning to fall.
The Bad
- Driver support still lacking in the NVidia department.
Overclock3D Performance Award
Were it not for the price of a Quad SLI setup I would not hesitate in giving the cards the much coveted Editors choice award. The Quad SLI setup does however deserve the performance award as despite the difficulties I had in getting Crysis to perform as it should, I believe it was a driver issue and not the cards themselves and once working as they should I was blown away with how good they really are. So regardless of the price, if you want the best you are simply going to have to pay for it.
Many thanks to XFX for providing the 9800GX2 cards and 790i Ultra motherboard for this review.
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