Dual Dealing: nVidia SLI vs ATi Crossfire

For gamers with deep pockets, ATi and nVidia’s recent multi-GPU arrivals have serious pulling power. Windows puts these dual technologies to the test…

  • E-Mail
By  Matthew Wade Published  May 4, 2006

|~|SLI-vs-ATI---medium.jpg|~|nVidia's SLI set-up will cost you the most, but you'll get some serious performance for your money.|~|If you’re in possession of a high-specification PC and a huge CRT or LCD screen with a stratospheric resolution, you’re already on your way to gaming nirvana. However, reality in the form of lagging performance will smack you in the face if you attempt to run any of today’s hottest titles (such as F.E.A.R) at maximum resolution, in full detail and with antialiasing (AA) enabled. Antialiasing basically smoothes the jagged edges of graphics. While the result is positive however, the load on your processor and graphics card increases exponentially. In most cases this results in slower frame rates. Therefore regardless of how immersive the game you’re playing is, if you start to notice performance stutters or jerks, the whole experience is destroyed, or worse still your game will become unplayable. The human eye can recognise up to 30fps (frames per second) at a time, which to us looks like fluid motion. As a result, most gamers aim to achieve a frame rate of 60fps at their preferred resolution. This is because if a stutter occurs, it won’t really be noticeable, unless the performance hit is so heavy that performance drops by over 50% (or below 30fps). While today’s hottest graphics cards from ATi (the X1900 XTX) and nVidia (with the GeForce 7900 GTX) are capable of stellar performance with full screen antialiasing enabled, even these monsters will struggle once the resolution goes past 1600 x 1200 pixels. The solution? Invest in a multi-GPU set-up. Both ATi and nVidia now offer this technology (known as CrossFire and SLi - Scalable Link Interface - respectively), which sees two graphics cards working in tandem to boost performance. However, these technologies work in different ways. How they differ The most obvious difference is a physical one. ATi makes use of an external dongle cable (a wire that links both cards and includes a separate monitor output). This links the two graphics cards together. nVidia relies on a snap-on bridge connector, which is physically the neater of the two approaches. In ATi’s case, you need to buy Master and Slave cards for the solution to work (this is shown on CrossFire compatible cards’ packaging). Strangely enough, Master cards (also known as CrossFire cards) are based on the X1900 XT specifications and not ATi’s top of the line XTX (the XT runs its core and memory at 625MHz and 1.45GHz while the XTX is clocked at 650MHz and 1.55GHz). You can however mix a CrossFire Master card with an X1900 XTX card but the XTX will simply end up waiting for the XT. In contrast, any two matching nVidia cards can be paired up meaning you can use the firm’s highest end GPUs (7900 GTX) together. In terms of how two cards work to better performance, nVidia uses each card to render alternative frames. CrossFire on the other hand can make use of three different rendering techniques. With the first, the card breaks the entire screen up into squares (known as tiles) and splits the rendering load between the cards. The second way (as with SLI) has the two cards rendering alternative frames, while the third approach sees the screen split into two halves, with each card rendering one half. ------------------------- OUR TEST RIGS ATi CrossFire AMD Athlon64 FX60 (dual-core 2.6GHz) processor, 512Mbytes x2 Corsair DDR400 (dual-channel mode), Asus A8R-MVP motherboard (ATi CrossFire Xpress 3200 chipset), Western Digital Raptor X Serial ATA hard drive, Gigabyte GO-W1616C optical drive, Viewsonic Ultrabrite E92f+ CRT monitor, Windows XP Professional SP2 Drivers: ATi Catalyst 6.4. nVidia SLI AMD Athlon64 FX60 (dual-core 2.6GHz) processor, 512Mbytes x2 Corsair DDR400 (dual-channel mode), MSI K8N Diamond Plus (nVidia nForce4 SLi X16 chipset), Western Digital Raptor X Serial ATA hard drive, Gigabyte GO-W1616C optical drive, Viewsonic Ultrabrite E92f+ CRT monitor, Windows XP Professional SP2 Drivers: nForce4 x16 chipset driver version 6.85, nVidia Forceware 84.21 graphics card driver. ------------------------- Put to the test We tested each set-up on a different motherboard because there’s no one chipset available right now that supports both multi-GPU technologies. We tested each set-up using our standard benchmarking suite at three resolutions - 1024 x 768, 1600 x 1200 and 1920 x 1440 pixels. While 1024 x 768 puts a fair amount of load on the PC’s processor, 1600 x 1200 and 1920 x 1440 rely on GPU power for higher performance. Each set-up was tested first using just a single card, with full screen antialiasing set to 4x. Then when running in multiGPU mode, we tested each with and without 4x AA turned on. The numbers game In terms of our test results (see below), the benefits of a multi-GPU set-up are undeniable. Quality on both systems was absolutely stunning owing to the high resolutions and antialiasing. It’s worth noting however that unless you’ve got an extremely fast processor in your PC, the performance benefits you get at lower resolutions such as 1024 x 768 will be restricted, because at such resolutions the GPUs end up waiting for the CPU to process data. The reverse is true at higher resolutions, when there’s more load on the graphics cards. Having said that, both the CrossFire and SLI solutions really make playing at high resolutions with all the details enabled a joy. F.E.A.R for instance - at 1920 x 1440 pixels with 4x AA enabled - ran at 64fps on nVidia's SLI set-up and 60fps on on nVidia’s SLI and 60fps on ATi's CrossFire. These are very playable frame rates and the game reported no dropped frames or stutters at all. Disabling AA, the systems performed even better (though you’d never be able to tell the games were running faster without running benchmark software). The win in our F.E.A.R test went to nVidia as it trounced the CrossFire solution. We observed similar nVidia-biased results in 3DMark2003. The only test that ATi’s CrossFire managed to win was 3DMark2005. If you’re looking for the fastest gaming machine money can buy then, nVidia’s SLI is the multiGPU set-up to own at the moment (see below to find out how much this will cost you). Our best guess is that nVidia’s SLI offered better performance because it allows you to run two of the firm’s highest-end GPUs (the 7900 GTX) together (whereas ATi’s CrossFire forces you to settle for only its second-best GPU - the X1900 XT). Another possible factor contributing to nVidia’s win is the fact that ATi’s drivers aren’t as fine-tuned as nVidia’s. Looking ahead, we would be interested to see whether these results remain the same if our tests were run on a higher resolution display (above 1920 x 1440 pixels). However, these are difficult to come by at present. Watch this space… ------------------------- Costs compared ATi Crossfire Asus A8R-MVP motherboard - $240 ATi Crossfire Master & X1900 XT slave card - $1176 Enermax Noisetaker 600W power supply - $180 Total: $1596 nVidia SLI MSI K8N Diamond Plus motherboard - $228 XFX GeForce 7900GTX 512MB XXX Edition x2 - $1658 Enermax Noisetaker 600W power supply - $180 Total: $2066 ------------------------- ------------------------- FULL TEST RESULTS Click here to download the Excel spreadsheet. -------------------------||**||

Add a Comment

Your display name This field is mandatory

Your e-mail address This field is mandatory (Your e-mail address won't be published)

Security code