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Do-It-Yourself Quad-SLI: It's Official
Date: Aug 09, 2006
Author: Marco Chiappetta
Introduction to Quad-SLI

For almost a year now, NVIDIA has been teasing enthusiasts with their Quad-SLI technology. It was back in January at the Consumer Electronics Show that we got our first glimpse of a Quad-SLI based system, the Dell XP 600 Renegade.  That first Quad-SLI implementation consisted of four GeForce 7800 GTX GPUs, each coupled to 512MB of graphics memory, for a grand total of 2GB of frame buffer memory. Although it looked like four separate graphics cards were used to build up those early Quad-SLI systems, it was actually two. Each GeForce 7800 GX2 card as they became known consisted of a main 512MB GeForce 7800 GTX with a secondary daughter-card mounted to one side. The GPUs each got their own slim coolers, and the main- and daughter-cards communicated to each other through a proprietary link. Then two GeForce 7800 GX2 cards were installed into an appropriate nForce 4 SLIX16 based motherboard, and linked together via a pair of SLI connectors. NVIDIA also developed a proprietary switch for these early cards that allowed each 7800 GX2 card to interface with a single PCI Express X16 slot for full bandwidth operation.


NVIDIA's Booth at the 2006 Consumer Electronics Show

Those early GeForce 7800 GTX based Quad-SLI systems we saw at CES never fully materialized, however.  Instead, NVIDIA updated those early GX2 cards with the re-vamped G71 GPU and created the GeForce 7900 GX2. The GeForce 7900 GX2 required less power than the early 7800 GTX-based cards, which allowed NVIDIA to clock them higher and eliminate a proposed external secondary power supply requirement.  A smattering of 7900 GX2-based Quad-SLI systems were sold through a handful of strategic partners for a time, but they too never became widely available.  And disappointingly NVIDIA never allowed their partners to release GeForce 7900 GX2 at retail.

Then, in June of this year NVIDIA unveiled the GeForce 7950 GX2.  The 7950 GX2 was powered by essentially the same GPUs as the 7900 GX2, but the 7950 was based on a streamlined PCB that was much smaller than its predecessors.  NVIDIA was able to do this by dedicating only half the number of PCI Express lanes to each GPU and redesigning the PCB and slim-coolers altogether.  Another major difference was that NVIDIA launched the GeForce 7950 GX2 at retail.  On the day of launch, enthusiasts could finally buy dual-GPU powered GeForce 79050 GX2 video cards from their favorite e-tailers.  But, at launch, NVIDIA wasn't quite ready to endorse Quad-SLI for the Do-It-Yourself market.  Quad-SLI was only supported when purchased in a full system built by an approved partner.  NVIDIA took this route to ensure Quad-SLI owners had a good experience and didn't have to contend with incompatibilities or other potential pitfalls.

A few months have passed since the GeForce 7950 GX2 was officially unveiled though, which has given NVIDIA the time they needed to fine-tune and solidify the Quad-SLI platform as whole.  And today, with the impending release of a new set of Forceware drivers, Do-It-Yourself Quad-SLI is officially supported by NVIDIA.

We're going to show you all what it takes to assembly and configure a Quad-SLI system here today, but before we do, want to highlight a few previous HotHardware articles that explain much of the underlying technology at work in the Quad-SLI platform. We've covered the features and specifications of the G71 GPU in a couple of previous articles, and have taken a comprehensive look at the main features of the GeForce 7 Series and NVIDIA's multi-GPU SLI platform as a whole as well.

We know that's a lot of reading, but the information and performance data in the articles listed above will give you all of the background and architectural details necessary to fully understand the technology employed in a Quad-SLI based system. If you're unclear about anything on the proceeding pages, please look back to these articles for more detail.


Quad-SLI Components: Video Cards & Monitor

Of course, the main components in a Quad-SLI system are the GeForce 79050 GX2 video cards. For the purposes of this article, we got our hands on a pair of XFX GeForce 7950 GX2 cards.  If you've seen the 7800 GX2 and 7900 GX2 boards used in the first Quad-SLI systems mentioned on the previous page, you'll immediately notice that the GeForce 7950 GX2 is significantly smaller and more streamlined. In fact, the 7950 is about the same size as a single-GPU based 7900 GTX at approximately 9" long. The 7950 GX2 also has only one SLI connector at the top, as opposed to the two found on earlier 7800 / 7900 GX2s.

The GeForce 7950 GX2 is equipped with two GeForce 7950 GPUs, each coupled to 512MB of fast GDDR3 memory, for a grand total of 1GB of frame buffer memory per GX2. The 7950 GPU is based on the same G71 GPU used on the 7900 GTX; it's just clocked a bit lower. NVIDIA's reference 7950 GX2 specifications call for a 500MHz GPU clock with 600MHz (1.2GHz DDR) memory. XFX offers a couple of models, however, including the 570M XXX that's clocked much higher at 570MHz / 775MHz (1.55GHz DDR).


A Pair of XFX GeForce 7950 GX2 Cards

As we've mentioned, each GeForce 7950 GX2 is built from a pair of PCBs linked together through a proprietary interface. The two GPUs and on-board memory are outfitted with their own slim coolers. The GeForce 7950 GX2 requires only a single 6-pin PCI Express power feed, and cards feature a pair of dual-link DVI outputs along with an S-Video / HD component output. To use the GX2 in multi-monitor mode, however, multi-GPU mode must be disabled in the drivers, just like SLI.

Installing a pair of GeForce 7950 GX2 cards into a system and enabling Quad-SLI isn't just about framerate performance, however.  With Quad-SLI NVIDIA also introduced a new anti-aliasing mode, namely SLI32XAA.  SLI32XAA can be used in conjunction with 16X anisotropic filtering, to offer increased image quality in games that are CPU bound by such a powerful graphics sub-system. And Quad-SLI will also gives users the ability to play games at exceedingly high resolutions, which brings us to our choice of monitor.

Dell's 30" 3007FPW

To put it simply, Quad-SLI is not meant to be used with smaller monitors, or monitors that do not support ultra-high resolutions. If you've got a small monitor and don't plan to upgrade, stick with a single video card or a more mainstream SLI / CrossFire configuration.  Quad-SLI will work with virtually any monitor, but if its not capable of running at a high resolution, like 1920x1200 or 2560x1600, for example, there's really no point in using Quad-SLI.  At mainstream resolutions, a Quad-SLI system will typically be CPU-bound, and the graphics cards will not be fully utilized.

Based on our experience with Quad-SLI, we'd recommend using a monitor no smaller than 24" and a resolution no lower than 1920x1200.  In some circumstances, a monitor capable of 1600x1200 will be acceptable, but only if the user planned to use higher-levels of anti-aliasing and anisotropic filtering.  We went right to the top of the heap and acquired one of Dell's huge 3007FPWs.  The 3007FPW features a 30" LCD with a native resolution of 2560x1600.

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Quad-SLI Components: Mobo, CPU & PSU

Quad-SLI's motherboard requirements are similar to a standard SLI system.  However, we should note that the GeForce 7950 GX2 does not require a full PCI Express x16 electrical connection to function properly; a pair of 7950 GX2s will function in older nForce 4 SLI based motherboards. Because the traffic coming in is already comprised of 8 lanes on some SLI chipsets (from the chipset splitting a 16 lane PCIe connection into two 8 lane connections going to each PEG slot), the NVIDIA designed PCI Express switch used on the 7950 GX2 will interface with the 8 lane connection to the chipset, and just pass 8 lanes worth of traffic to each addressed GPU as needed. Technically Quad-SLI will work on all SLI capable chipsets like the NF590 SLI, 570 SLI, NF4 SLIx16, and standard NF4 SLI.

Although the NVIDIA PCI Express switch is compliant with the standard PCI Express specifications, the system BIOS of some motherboards may not properly recognize the 7950 GX2 right away. This was one of the hurdles NVIDIA wanted to overcome before endorsing DIY Quad-SLI. Without a properly configured system BIOS, the motherboard could fail to post or may not operate reliably with a 7950 GX2 installed. NVIDIA informed us that they have been working closely with motherboard manufacturers to have their system BIOSes updated to support the GX2, however. Refer to this site for a list of known compatible motherboards and the proper BIOS revisions that have been tested by NVIDIA. But please note the list on that site is not inclusive of all compatible motherboards, but rather reflects motherboards that have already been tested and qualified by NVIDIA. And don't be confused by the Intel and ATI-chipset based motherboards listed on that page. Those motherboards will work with a single 7950 GX2, but they are not Quad-SLI certified. 


The Asus P5N32-SLI SE Deluxe with a pair of GeForce 7950 GX2 cards installed

The motherboard that we used for our Quad-SLI project, the Asus P5N32-SLI SE Deluxe, was based on the NVIDIA nForce 4 SLIX16 Intel Edition chipset. The Asus P5N32-SLI SE Deluxe is a new revision of a motherboard that we've already reviewed here at HotHarware, the P5N32-SLI Deluxe.  The P5N32-SLI SE Deluxe is essentially revision 2.02G of the P5N32-SLI Deluxe. The majority of the motherboard was unchanged, but the P5N32-SLI SE Deluxe has an updated Quad-SLI compatible BIOS and a revamped VRM to fully support Intel's Core 2 Duo and Extreme processors.

The Asus P5N32-SLI SE Deluxe features true dual-PCI Express x16 graphics slots allowing full bandwidth SLI / Quad-SLI.  The PEG slot closest to the CPU socket is the primary graphics slot, and it's separated from the secondary PEG slot by a PCI Express x1 slot and a PCI Express x4 slot.  Installing a pair of GeForce 7950 GX2 cards into the P5N32-SLI SE Deluxe is the first step towards a Quad-SLI system.  With the cards installed though, clearance is a bit tight in some areas, like near the SATA connectors for example.

A Quad-SLI system also requires a powerful processor to feed its GPUs.  AMD's Athlon 64 FX processors and Intel's Core 2 Duo / Extreme are currently the best choices for a Quad-SLI system in our opinion.  For our build, we used Intel's flagship Core 2 Extreme X6800 processor.  As of today, this is the most powerful desktop processors available. We recently evaluated the Core 2 Extreme X6800 and Core 2 Duo E6700. If you'd like to delve a little deeper into the inner workings of these processors, click here.

PC Power and Cooling Turbo-Cool 1 Kilowatt

GeForce 7950 GX2 Supplemental Power Connectors

With four GPUs and a powerful processor at its heart, a Quad-SLI system has some lofty power requirements. Each GeForce 7950 GX2 can consume a peak of approximately 143 watts of power.  Double that number, and account for a CPU, RAM, hard drives, a motherboard, and a myriad of other components and you quickly realize that a run-of-the-mill power supply will not be able to meet the demands of a typical Quad-SLI system. For our build we used a PC Power and Cooling 1 Kilowatt (1000 watt) unit, but there are others available that would have worked just as well.  A list of certified power supplies is available on NVIDIA's SLIZone website.  When shopping for a Quad-SLI capable PSU, it's best to look for a model that has multiple 12v rails that can each meet the current demands of Quad-SLI.  It's not just about total wattage.


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Quad-SLI Components: Memory & Misc.


Another major component to a Quad-SLI system is RAM.  To coincide with the launch of the nForce 500 family of chipsets, NVIDIA also announced support for Enhanced Performance Profiles, or EPP.  EPP is a feature designed to maximize system performance by automatically tweaking memory and CPU frequencies, multipliers and voltages on compatible motherboards.

EPP is a new open memory standard that was co-designed by Corsair and NVIDIA and adopted by a number of motherboard and memory manufacturers. Enhanced Performance Profiles can increases performance by taking advantage of additional memory parameters added to the unused portion of a standard JEDEC Serial Presence Detect, or SPD.  The JEDEC specification only calls for small amount of data to be stored in a standard SPD, which leaves a significant amount of unused space.  EPP takes advantage of this space to store specific information about the modules, like their maximum supported frequencies, recommend voltages and timings.

Corsair's SLI Ready Memory

EPP also needs motherboard support to function as well.  To support EPP a motherboard's BIOS has to be programmed to snoop the upper portion of the SPD to find the EPP relevant data.  That data is then used in conjunction with a pre-determined set of parameters stored in the system BIOS to automatically tweak performance.

For example, if the EPP data stored in the SPD states a particular memory kit is capable of running at 1066MHz with 5-5-5-12 timings, EPP will automatically alter the processor's multiplier, voltage and bus speed, along with the memory voltage, to get as close to said memory's rated speed as possible. EPP will also overclock the processor by a user determined percentage to hit the memory's rated speed.

The Asus P5N32-SLI SE Deluxe that we used as the basis of our Quad-SLI build does not have support for EPP, but upcoming nForce 590 SLI will.  Although any memory will work in a Quad-SLI system, EPP equipped memory is usually of high quality and we recommend considering it. The rig we put together was equipped with a 2GB Corsair TWIN2X2048-6400C3 DDR2 memory kit capable of DDR2-800 speeds with relatively tight timings of 3-4-3-9.

For the rest of our Quad-SLI system, we used an HSPC Tech Station (case), an LG DVD-ROM drive, and a Western Digital WD1500 Raptor hard drive.  NVIDIA doesn't make any specific case or optical or hard drive recommendations. However, we can speak of some of our own general recommendations based on our experience.  In regard to storage, your preferred brands / models will be fine. Just ensure motherboard compatibility as some Maxtor hard drives had a known incompatibility with nForce chipsets.  As for the case, we'd recommend mid- or full-tower enclosures that have oversized intake and exhaust fans and preferably a vented side panel.  Having four GPUs and 2GB of fast GDDR3 memory in a system means there will be plenty of heat generated, and that heat has to be considered.  Consider good ventilation an absolute must.


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Building a Quad-SLI Rig

Assembling and building-up a Quad-SLI system is essentially the same as building a standard SLI system. Although there are some important things to consider when acquiring the components (motherboard compatibility, power supply, cooler, etc.), the actual assembly process is not difficult.  Anyone that has experience assembling PCs should also be able to put together a Quad-SLI rig.

Memory & Graphics cards installed

The memory and processor get installed in the motherboard just like any other system.  Then the GeForce 7950 GX2 cards each get inserted into their own PCI Express x16 graphics (PEG) slot and linked together via an SLI connector that slips over the "gold-finger" contacts at the top of each card.  We assembled our system in an open air tech station to make it easier to illustrate the process, but the process is the same for any case once the motherboard has been mounted.

Clearance between and around the graphics cards

There are a few things to consider when assembling the system.  With two double-wide graphics cards installed, a number of expansion slots will be unusable and some on-board ports and headers may be obstructed as well. As you can see in the pictures above one of the P5N32-SLI SE Deluxe's PCI slots and one PCI Express x1 slot are blocked by the 7950 GX2 cards.  And there is limited space between and below the graphics cards

Connect your monitor to the graphics card in the first PEG slot

Once you've got everything assembled, your monitor should be plugged into the graphics card that's installed in the first PEG slot to initialize during the POST(this can be set in the system BIOS). This is typically the first PEG slot, closet the to processor on nForce-based motherboards.  We'd also recommend flashing the motherboard to the latest BIOS available on the manufacturer's website.  We used the v0204 BIOS for the Asus P5N32-SLI SE Deluxe featured here.

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Configuring the System

Once your hardware is assembled and you've got the operating system installed (we used Windows XP SP2), there is still a bit of work to be done to properly configure a Quad-SLI system.  The first thing that should be done, is install the proper chipset drivers for the motherboard.  We used the nForce v6.86 drivers for the nForce 4 SLIX16 Intel Edition chipset, but there are other packages available for download for the other members of the nForce family. You can reference NVIDIA's driver download page for the latest versions.

NVIDIA nForce Chipset Driver Installation

The chipset driver installation is simple and straightforward.  Just run the setup file and follow the on-screen prompts.  We should note, however, that we typically do not install NVIDIA's audio drivers. Instead we usually opt for reference drivers from the manufacturer of the motherboard's integrated audio codec. In the case of the Asus P5N32-SLI SE Deluxe, we used Realtek's v3.91 AC'97 drivers.

Once you've got the chipset drivers installed, we recommend updating the operating system to get the latest patches and security fixes. It's also important to make sure you've got the latest version of DirectX installed for optimal performance and compatibility. The latest distribution (August 2006) can be downloaded here

SLI Configuration Page in NVIDIA's Forceware v91.37 Drivers

With the chipset drivers installed and the OS patched and up-to-date, it's time to install the video drivers. Like the chipset drivers, installing NVIDIA's Forceware graphics drivers is very easy.  Run the setup file and step through the on-screen prompts until the process is complete.  You may be warned during the installation that some files are not WHQL certified, but this is usually not an issue.  Just click OK and move forward through the installation.

When the graphics driver installation is done and the system restarts, you'll typically be greeted by a balloon dialog that'll direct you to the SLI configuration page pictured above.  It's on this page that you can enable Quad-SLI.  With Quad-SLI disabled, the two GeForce 7950 GX2 cards in the system will work independently. There are a multitude of other options available within NVIDIA's Forceware rel. 90 drivers as well.  For more information on those, see here.

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XHD Gaming Experience

NVIDIA developed Quad-SLI with ultra high-resolution gaming in mind. To that end, we fired up a few of today's popular games to see how our Quad-SLI rig fared at the native 2560x1600 resolution of our Dell 30" 3007PFW flat panel.  We'll be taking a different route in this article that we normally would, however.  We did not run our standard suite of benchmarks this time around.  We recently tested a Quad-SLI configuration in this article and have detailed the performance characteristics there.  What we want to do here is try to show you what a Quad-SLI rig offers to gamers.

F.E.A.R. - Resolution 2560x1600 (4X AA / 16X Anisotropic)
Framerate = 46 FPS
Click to View Full-Resolution Image

The first game we fired up was F.E.A.R.  Unfortunately, F.E.A.R. did not support our flat panel's high resolution our of the box so we had to do a little "tweaking".  To get F.E.A.R. to run at 2560x1600, we first launched the game and set our desired graphical options, saved the changes, and exited the game.  Then we went into the game's configuration file and manually entered the screen width and height attributes. And at this point we were ready for some ultra high-res gaming.  Hopefully the screenshot above will give you an idea as to how F.E.A.R. looks at a resolution of 2560x1600. At this resolution, with 4X anti-aliasing and 16x anisotropic filtering enabled, the gamer registered a respectable average framerate of 46 frames per second.  We know that's not the kind of number gamers like to see, so we also tried the game with 2X anti-aliasing enabled, and at that point it hit a much better average of 85 FPS.

Half Life: Episode 1 - Resolution 2560x1600 (4X AA / 16X Anisotropic)
Framerate = 37.55 FPS

Click to View Full-Resolution Image

Next, we spent a little time gaming with Half Life 2: Episode 1. This addition to the Half Life 2 franchise has improved graphics and makes use of HDR rendering.  Fortunately, the game engine natively supported our flat panel's high resolution, so after choosing the appropriate options in the game's control panel we were up and running. At 2560x1600 Episode 1 looked fantastic, but with 4X anti-aliasing and 16x anisotropic filtering enabled performance was quite to our liking.  At that high-resolution with AA and aniso enabled, our Quad-SLI rig posted an average framerate of 37.55 FPS.  So, we knocked the AA down to 2X and the framerate jumped to a more acceptable 49.23 FPS.  Taking the anisotropic filtering down to 8x resulted in an even better average framerate of 52.21 FPS.

Prey - Resolution 2560x1600 (4X AA / 16X Anisotropic)
Framerate = 78.9 FPS
Click to View Full-Resolution Image

The last game we have to show you is the recently released Prey. Prey is based on an updated version of the Doom 3 engine, but it too unfortunately did not support our panel's high resolution right away.  To get Prey to run at 2560x1600 we had to enter a handful of commands in the console, but there are a number of ways to enable custom resolutions with this engine.  Because Prey was designed for OpenGL, it was the only game here to run in full 4-way AFR, which translated into higher performance.  With 4X anti-aliasing and 16X aniso, Prey posted a perfectly playable 78.9 FPS.

The fact that two of the three games we played requiring some sort of hack to get working at 2560x1600, proves that ultra high resolution widescreen gaming is still in its infancy, and Quad-SLI users will have to put in some extra effort to fully utilize their hardware. Luckily, there are already a number of resources on-line that explain how to enable custom resolutions with numerous games.  The Widescreengaming forum in particular is very helpful. 

What we can't easily show you with any of these screenshots, however, is how much more engrossing a game is when being played on a large monitor with a 16:10 aspect ratio.  The 16:10 widescreen aspect ratio means more of the game world is visible in your field of view. And when sitting in front of a large 30" panel like Dell's 3007FPW, portions of the screen are only visible in your periphery. It's somewhat like watching an iMAX movie where you feel more a part of the imagery, rather than a spectator looking through a window, as is sometimes the case with smaller 4:3 aspect monitors.


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Our Summary, Costs, and Conclusion

Assembling and configuring a Quad-SLI system was no different than putting together a standard SLI rig for the most part.  There are some hefty power requirements that should be taken into consideration and cooing is very important, but NVIDIA seems to have ironed out most of the technical wrinkles already. The system we assembled worked fine from the get-go with the applications we tested.  Any enthusiast that's comfortable assembling a standard SLI rig should have no trouble with Quad-SLI.

For Quad-SLI owners, configuring a system doesn't necessarily stop once the hardware is up and running, however. To take advantage of the high resolutions offered by today's crop of large monitors, many games have to be modified manually. For power users, we don't think this will be an issue, but for gamers that don't happen to be very tech savvy, taking advantage of what Quad-SLI offers could be somewhat difficult.  Keep that in mind.

Another major consideration for Quad-SLI is cost.  The parts needed to assemble a worthwhile Quad-SLI system are considerably expensive at this time.  The products we used for our build consisted of the following core components...

Core 2 Extreme X6800 - $1300
XFX GeForce 7950 GX2 - $570 x 2
Corsair TWIN2X2048-6400C3 - $400
Asus P5N32-SLI SE Deluxe - $250
Turbo Cool 1 Kilowatt - $500
Dell 3007WFP - $2199
Total Cost - $5789

* Current "Street" Prices

As you can see, we were approaching the $6000 mark with just the core components to a high-end Quad-SLI rig. We did not take into account a case, drives, input devices, a dedicated sound card, or any other accessories for that matter.  Clearly, Quad-SLI is not for everyone; then again it isn't meant to be. But for those that can afford the hardware, there is currently nothing more powerful when it comes to graphics performance.  And as NVIDIA further optimizes their Forceware drivers, Quad-SLI performance and compatibility should only get better.

Undoubtedly, Quad-SLI is a niche product / platform.  But once costs come down as they inevitably always do, this type of system will likely become more popular with enthusiasts. And it seems NVIDIA has the foundation in place to make moving to a Quad-SLI rig relatively painless.

** Update: NVIDIA has the Forceware v91.45 drivers on-line now.

  • High Performance @ High Resolutions
  • Great Image Quality
  • Mature Platform
  • Relatively Easy Assembly
  • Needed to modify some games for 2560x1600 res.
  • Somewhat Noisy
  • Power Requirements

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