Date:
Tuesday , November 23, 2004
Author:
Brent Justice
Editor:
Kyle Bennett
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NVIDIA SLI Upgrade Guide

Thinking about upgrading to a gaming rig powered by NVIDIA's Scalable Link Interface? We tell you what you need to know by showing you what type of gaming experience you can expect in Half Life 2, DOOM 3, and FarCry with focus on where your SLI upgrade path will lead you in terms of image quality.

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SLI Upgrade Guide Objectives

I am sure that some of you are wondering why we are calling this a “guide” instead of a “review”. There will be plenty of “reviews” today, so we wanted to cover this from a little bit different slant. Going to an SLI rig may be “no-brainer” decision for some of you but there are many gamers out there wondering exactly what it will deliver for their hard earned dollars. If you do make the call to build a SLI rig that will be upgraded with a second video card in the future, you will want to carefully choose what flavor of GPU you buy for your initial install. Meaning, do you start with a 6600GT, 6800GT or 6800 Ultra? If you are constrained by budget, obviously the 6600GT may the way to go for you, but then again, would saving your pennies for another couple of months in order to go with a 6800GT be a better value for you in the end? Or would going with a less expensive motherboard (SLI motherboard prices should be in the sub-$200 range once supply is solid.) with a single slot solution be better for you? For you ATI owners, we will also show you how your solutions stack up against NVIDIA’s.

Bottom line we hope to show whether or not SLI is right for you and if it is, what video card(s) would likely be a fit for your project.

Enabling SLI

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With one video card operating in single card mode the ForceWare drivers detect that the card is capable of SLI and notifies you that you can in fact take advantage of the SLI setup with another SLI video card.

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Once you have your two GeForce 6600GTs, 6800GTs or 6800Ultras you will need to reinstall the connector card on the motherboard so that the “dual video” side is inserted into the connector slot. In its default configuration it is set for Single Video Card operation. Turning it around enables SLI and sets both PCI-Express ports to PCI-E X8 operation. Do this step before you install the video cards to ensure you have room to work.

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Next you must install both video cards in the PCI-Express slots and connect them together with the provided SLI bridge connector. This little piece of technology can move data at 10GB/sec between the cards.

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After you have installed both video cards, connected the bridge together and enabled SLI operation in the motherboard BIOS you can go ahead and boot your machine. Clicking on the balloon pop up will bring you to the SLI configuration tab in the ForceWare drivers. From here there is only one check box needed to get SLI working. There is another check box which lets you select if you wish to view load balancing. This shows you in-game if it is using Split Frame Rendering (SFR) or Alternate Frame Rendering (AFR) and how much work each card is doing. After you select these options it will ask you to restart.

SFR and AFR describe how SLI is being done in a particular game. Most new games will allow SFR to be done. This allows both video cards to share the workload of any single frame shown on the screen. However, some games do not play friendly with SFR and there require AFR. With AFR, each card draws every other full frame. AFR is not as efficient as SFR in most cases, but does solve some issues when SFR does not output the desired image. Profiles are set up in the driver to help selection of the appropriate mode and should be invisible to the user. That said, it will be very likely that SLI users need to update their driver set as newer games are purchased. It will be interesting to see how this works out.

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Then a balloon pops up telling you SLI has been enabled and that is all there is to it. SLI installation could not be much easier.

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You will notice after you have flipped the card on the motherboard to “Dual Video Cards” the bus interface now reads as “PCI Express X8” indicting that your transfer rate is at X8 instead of X16 as it would be in single slot configuration.

Test Setup:

ASUS A8N-SLI Deluxe (nForce4), AMD Athlon 64 FX-53, 2 x 512MB Corsair XMS PC3200LLPro TwinX Dual Channel DDR400, Western Digital 74GB Raptor SATA/150, Windows XP Professional SP2 with DirectX 9.0c.

and

ABIT AV8 (VIA K8T800), AMD Athlon 64 FX-53, 2 X 512MB Corsair XMS PC3200LLPro TwinX Dual Channel DDR400, Western Digital 74GB Raptor SATA/150, Windows XP Professional SP2 with DirectX 9.0c.

eVGA GeForce 6600GT PCI-Express – Operating at default clock speeds 500MHz/1GHz using ForceWare 66.93.

NVIDIA GeForce 6800Ultra PCI-Express – Operating at default clock speeds 400MHz/1.10GHz using ForceWare 66.93.

NVIDIA GeForce 6800Ultra PCI-Express downclocked to 6800GT speeds at 350MHz/1GHz using ForceWare 66.93.

ATI Radeon X800XT-PE AGP – Operating at default clock speeds 520MHz/1.12GHz using Catalyst 4.12 Beta.

ATI Radeon X800Pro AGP – Operating at default clock speeds 475MHz/900MHz using Catalyst 4.12 Beta.

We ran all GeForce PCI-Express video cards on the ASUS A8N-SLI nForce4 platform in single card and dual card SLI configurations for this testing.

We ran into some issues getting PCI-Express ATI Radeon X800XT-PE and X800Pro video cards working on our SLI motherboard. Therefore we used an AGP Radeon X800XT-PE and AGP Radeon X800Pro on the ABIT AV8 platform with the same CPU and RAM. There is no difference in gameplay performance between the PCI-Express and AGP8X bus so this comparison does work.

At this time the only driver that is compatible with SLI is ForceWare 66.93, that is why we used that driver version instead of the Beta 67.02 available from NZone. We used the default control panel settings on each video card. For the ForceWare drivers this means Trilinear Optimization was ON, Anisotropic mip filter optimization was OFF and Anisotropic sample Optimization was ON.

We did use the Catalyst 4.12 Beta drivers which are available here from ATI’s support infobase webpage. We used the default CATALYST A.I setting and disabled VSYNC.

We will look at gameplay evaluation performance in three of the top games of today, DOOM 3, FarCry and Half Life 2 making comparisons.