nVidia brings back SLI for PCI Express - Two is always better than one

It's back! SLI is back from the dead. 3DFX were the first to bring dual graphics cards to the personal computer back in 1998. Six years later, today nVidia re-introduces SLI with the GeForce 6800 GT and Ultra. We have all the information inside on the latest graphics technology to emerge on the market.
Cameron Wilmot
Published Sun, Jun 27 2004 11:00 PM CDT   |   Updated Tue, Apr 7 2020 12:26 PM CDT
Manufacturer: none

nVidia SLI - Introduction

IntroductionUsers who have only just entered the personal computing realm over the past couple years did not have the privilege of experiencing the rise of the enthusiast computer user and the resulting and exciting new market segments, especially in the graphics card department.Back in 1998 when 3DFX were in their prime, the then strong company released the VooDoo2 graphics chip with the option of running two 3DFX based PCI graphics cards in one system with the aim of increasing gaming performance. This method is called Scan Line Interleave or SLI for short. Back then, if you had an SLI enabled system, you were the most popular geek on the block, no questions asked. For many, it sparked a strong interest in the internals of the personal computer and as a result helped create a new generation of computers users: the enthusiast.
nVidia has stepped up the graphics performance of person computers in a big way today for the enthusiast and graphics professionals with the introduction of their own PCI Express 16x graphics cards with support for "Scalable Link Interface", or again SLI for short. Unfortunately we don't have an nVidia PCI Express SLI test system here today but we do have all the latest information on the technology for you.We flew up to Sydney last week to hear nVidia's claims for SLI. Read on as we document everything we learned during the press conference.

nVidia SLI - Previous implementations of SLI

Previous implementations of SLITo get a better appreciation for SLI, here are some previous implementations of SLI from 1993 to 1998.Back in 1993, if you wanted an SLI system (classed as super computer), it would have cost you upwards of $250k.
The result of this quarter of a million dollar investment was being able to play a flight simulator at just a few frames per second, as you can see below.
Fast forward a few years then we entered the exciting 3DFX VooDoo2 realm of SLI.
This technology enabled gamers to play their favorite games at relatively high resolution of 1024x768, as you can see in the shot below with Quake2. With a single VooDoo2 card, it was just about impossible to play at 1024x768 as the frame rate was very low. SLI allowed gamers to play Quake2 at 1024x768 at the same frame rate as 800x600 by increasing performance by around 20 - 25%.
Now you've got a bit of an idea about previous SLI implementations, let's take a look at nVidia's brand new SLI technology and their plan of attack for the industry.

nVidia SLI - nVidia's implementation of SLI

nVidia's implementation of SLI
nVidia's implementation of SLI is quite a bit different than the previous methods we saw on the last page. From what we can see, nVidia has extensively studied the old 3DFX SLI technology and improved on every aspect of the technology to create their own breed of modern SLI which can currently be utilized with their Quadro, GeForce 6800 GT and Ultra flavors (only).- High Speed Digital InterfaceCompared to the 3DFX technology for one, there is no longer the need of having a messy array of cables connecting the cards at the back of your system for visual output. With nVidia's PCI Express SLI, all these tasks are performed internally using the "High Speed Digital Interface" which connects both cards together using a simple SLI connector which plugs into the cards "MIO" port, as pictured below on our reference 6800 Ultra PCI Express sample.
The cards are then connected using an SLI connector which you can see below. The connector is essentially just a small circuit board with two MIO connectors (or plugs).
Compared to 3DFX's method of connecting the cards with a cheap ribbon cable, the new implementation from nVidia just feels much better. It's something I would have more confidence in.

nVidia SLI - nVidia's implementation of SLI Continued

nVidia's implementation of SLI Continued- Enabled by PCI Express
nVidia's SLI method is enabled by PCI Express, namely the upcoming Intel Tumwater server chipset. The Tumwater chipset natively supports dual PCI Express 16x which can be implemented (or not) by choice of the motherboard manufacturer.You might be wondering why we never saw SLI for AGP from nVidia over the past few years. The answer is really quite simple. There was not much market demand for AGP SLI and as a result, none of the chipset companies bought any products of this nature to the consumer. However, given what I've just said, if nVidia, ATI or any other graphics company wanted to produce AGP SLI solutions, the industry probably would have supported the move, as long as the consumer demand was present. Whenever there is a decent demand for something, IT companies will respond by making the required product available.
You could be thinking nVidia is taking a risk by producing SLI enabled cards as the market for these types of system is very small, since the cost of overall implementation is high. The fact is, it doesn't cost nVidia all that much to implement SLI supporting technology into the latest graphics chips - it's actually been present in nVidia's GPU's for a few years now. nVidia's Add-in-Board partners will be able to decide whether or not they want to add the MIO connector to their GeForce 6800 GT and Ultra cards when they finalize their PCB designs. The cost of this is fairly minimal so you can probably expect to see the majority of PCI Express 6800 GT and Ultra cards from nVidia's Add-in-Board partners to come with the MIO connector, as an added feature.- Dynamic Load Balancing and Performance ClaimsnVidia's upcoming Forceware drivers (probably in the 60.xx range - nevertheless, nVidia SLI driver technology is ready right now and is just itching to be released by all accounts) handle most of the load balancing work for nVidia's PCI Express SLI - that is, the determining of which card will handle what part of the screen. Like the recently announced Alienware dual PCI Express system, at this stage each GPU will be in charge of one half of the screen (top and bottom). nVidia were tight lipped on exactly how this will work but did mention as the technology matures, they will be able to handle load balancing techniques in more advanced and impressive ways.The good news is nVidia's PCI Express SLI technology "will just work". Meaning, game developers aren't required to release any new patches to support the new technology (at least according to nVidia). nVidia's drivers will take care of the entire process in the background.
nVidia claims performance increases under 3DMark03 up to 1.87 times faster than a single graphics card system. These numbers are based on settings of 1600x1200 with 4x AA and 8x AF.
As you can imagine, the higher you increase the resolution and the higher image quality settings you choose to use with SLI, the faster the performance gain will be relative to non-SLI as GPU performance becomes more critical than CPU and memory sub-systems. Hence the reason nVidia choose these settings but in nVidia's defense, you'd have to be pretty silly to be playing a game at 1024 x 768 with no AA or AF with an SLI system.nVidia mentioned the typical performance increase you will see is around 60%.

nVidia SLI - Down Sides to nVidia's SLI

Down Sides to nVidia's SLIWhile nVidia's PCI Express SLI technology sounds great on paper, there are a few down sides we need to mention.- Server class only?At this stage it seems like the only way you'll be able to experience nVidia SLI is by buying a server class motherboard, based on the Intel Tumwater. From what we were told, the Tumwater is currently the only chipset to support dual PCI Express 16x slots.
If and only until PCI Express SLI becomes popular at a semi-mainstream level, don't expect to see too many chipset makers produce desktop chipsets with dual PCI Express 16x slot support. On the other hand, it seems highly feasible that nVidia would support dual PCI Express 16x slots in their upcoming nForce desktop chipsets to help move more of their VGA product. Unless ATI turns around and creates their own SLI technology, don't expect the Canadian firm to create support for dual PCI Express 16x in any of their upcoming chipsets.- Power HungryThe minimum power supply recommendation for a single GeForce 6800 Ultra system is 350 watt, double that then you have 700 watt. The recommended power supply if you intend on overclocking your system with for a single GeForce 6800 Ultra system is 500 watt, double that then you have 1000 watt.Let's say you need 200 watts per card, you then have a total of 400 watts for the duo. Add an extra 200 watts or so for the rest of the system, you're at around 600 watts - at a minimum. The math speaks for itself here. If you are intending on using nVidia SLI, keep in mind the type of power supply you'll need and the associated costs which are involved with such a project. Everything starts to make sense now after seeing several 800 watt power supplies while walking around the halls at Computex in Taiwan earlier this month.- Extreme Performance = Extreme CostWith Extreme Performance SLI comes Extreme Cost. We did some quick checks on PSU, the graphics cards and server motherboard. For these three components, you're looking at around $2,300 US (roughly $3,300 AU) without even considering other parts of the system, such as the expensive Intel Xeon processor to go along with the Tumwater motherboard.At the early stages, be prepared to reach deep into your pockets if you want SLI technology in your personal computer. As SLI becomes more popular and the demand for higher capacity power supplies, etc become more widespread, it will eventually help reduce the price and increase the affordability of PCI Express SLI in general.- Mixing of CardsOne question we quickly had answered by nVidia was whether or not we could mix and match graphics cards. The short answer is, no. You need to be running the exact same graphics card for SLI to work properly.
If you're into overclocking, it was even suggested you overclock both cards at the exact same clock speeds to be safe. The down side to this could be if you have one card which overclocks very well and another which only has mediocre overclocking performance, you will need to adjust both cards clock speeds to the lowest common denominator.Mixing both ATI and nVidia cards under SLI was laughed off fairly quickly during our press conference in Sydney but it would be rather interesting if someone figured out how to hack SLI to mix ATI and nVidia cards together.

nVidia SLI - Final Thoughts

Final ThoughtsWith the re-introduction of SLI, it is clear to see that the 3DFX influence inside nVidia is still well and truly alive and kicking. It's fantastic to see nVidia bringing back SLI again for the hardware enthusiast community to feast over and we expect it will be welcomed with big wide open arms. The new and improved SLI technology should do a tremendous job of regenerating a lot of tired users who have become bored with less than exciting personal computer technologies over the past while. Sure, we now have DDR-II memory, 64-bit processors and PCI Express card slots but we won't see these new technologies increase performance dramatically for the average consumer for a little while yet.With nVidia's implementation of PCI Express SLI, we are able to see performance increases over single PCI Express graphics cards system of up to almost 90% in some instances. The typical performance increase we will see will be closer to 60% but that is still very impressive and will help the transition from impressive to life-like realism computer gaming graphics in a shorter amount of time as image quality settings such as Antialiasing and Anisotropic Filtering are ramped up even more.To the best of our knowledge, it seems like you'll need to an expensive server class motherboard based on the Intel Tumwater chipset for the Intel Xeon processor, if you want SLI, as it's currently the only chipset with dual PCI Express 16x support planned. You'll need a powerful power supply capable of dishing out at least 600 watts of power and the cash to go along with buying the complete system. We suspect nVidia will release upcoming nForce chipsets in the near future with dual PCI Express 16x support which will make the upgrade path to SLI much more feasible than moving to an expensive server grade platform.nVidia PCI Express SLI should be an instant winner in the "Ultra Enthusiast" market segment for those who demand the absolute best of the best computing performance. However, for those users who don't have as much cash to dish out, it might take a little bit longer to sell, while these users wait for the technology to become more mainstream and as such, more affordable and obtainable.nVidia has raised the graphics performance bar, how will ATI and others respond? Thanks for making life more interesting, nVidia.

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Cameron founded TweakTown in 1999 after it originally started off as his personal homepage. Cameron was once, many years ago, the only person at TweakTown producing content, but nowadays, he spends his time ensuring TweakTown operates at its best in his senior management role.

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