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ASUS A8N-SLI Deluxe and N6600GT

By Matthew Overington

Nvidia’s long-awaited chipset allows two video cards to run side by side. Matthew Overington investigates.

02, May 2005 - It’s no secret that gaming is massive. In fact, the US$10 billion games industry has already overtaken Hollywood in terms of revenue, driving the demand for high-performance hardware which can make the most of today’s top gaming titles. After Intel released its 9xx-series chipsets in 2004, the AMD64 platform fell behind a little when it came to chipset features. Intel had the lead on PCI Express support and native DDR2 memory, leaving AMD customers, many of them performance-hungry early adopters, longing for chipset updates.

AMD has caught up, though, as ATI and Nvidia have announced new chipsets for the 64-bit processors with features that even the Intel-compatible solutions lack, including support for Serial ATA II and a clever video system upgrade.

The Nvidia nForce4 series chipsets are available in three flavours: regular, SLI and Ultra. The base model includes a basic hardware firewall, PCI Express, RAID, Gigabit Ethernet and Serial ATA (150MB/s) support. The Ultra and SLI models include all this, plus support for Serial ATA II (375MB/s) and updated hardware protection called ActiveArmor that palms off packet-filtering tasks to a hardware module, freeing up CPU time.

The only major difference between the Ultra and SLI models is that the SLI can drive two graphics processors simultaneously. This splits the processing load across the two cards, which requires specially engineered motherboards (like the ASUS A8N-SLI), two identical SLI-compatible video cards and an SLI bridge to link the two cards together. This is the gamer’s equivalent to fitting two processors to a system to speed up complex, CPU-intensive tasks and has been promised as the solution for next-generation video performance. Currently Nvidia is the only video manufacturer looking at SLI implementations — ATI has announced that it isn’t going to provide support in the near future.

SLI requires a motherboard with two PCI Express x8 lanes and two identical, SLI-compatible video cards, which has required a substantial investment in new engineering from Nvidia. Currently the company has only announced SLI compatibility for GeForce 6600GT and GeForce 6800GT cards, though the range is expected to increase further down the track as new cards are announced.

The system works by splitting the screen in half and the processing between each card. The cards “talk” to each other directly via a bridge — either a ribbon cable or a printed circuit board (PCB) — and output the rendered result via one of the video card’s VGA or DVI ports.

REINVENTING THE WHEEL
Although this sounds like a clever new trick to boost video performance, it’s actually a recycled concept. The now-defunct company 3Dfx pioneered the technology with its range of Pure 3D II cards, which also had the ability to split rendering duties across two video processors. The system relied on two PCI-based video cards linked directly via a cable. 3Dfx also called its technology SLI, though it stood for Scan Line Interleave, not Scalable Link Interface.

Nvidia decided that the way to push video performance beyond its thresholds was to dredge up this older concept and rework it for modern architecture. The two systems differ in one key area: 3Dfx relied on each card to render alternate scan lines, rather than assigning a section of the screen to each. The 3Dfx solution fell by the wayside with the advent of AGP ports, as their design prevents two slots from running together on a motherboard.

FIRST LOOKS
APC managed to track down a number of ASUS components to put Nvidia’s SLI solution through the wringer. We started off with an A8N-SLI motherboard and matched it to two 128MB Nvidia GeForce 6600GT video cards. The motherboard ships with a PCB bridge: it’s not something you have to hunt down yourself. An Athlon 64 FX-55 processor, 1GB of PC3200 Kingston ValueRAM and 250GB Maxtor MaxLine III Serial ATA hard drive were then fitted and the SLI configuration was benchmarked against a single 128MB Nvidia GeForce 6600GT video card and ATI Radeon X800XT.

Nvidia claims a 1.87x performance boost by fitting two cards in an SLI configuration, though these figures couldn’t be matched during testing.In fact, at 1,024 x 768 under 3DMark2001 SE, both the ATI X800XT and single Nvidia GeForce 6600GT managed to marginally out-perform the SLI setup. This is because the overhead involved in getting the two cards to communicate effectively negates the performance benefit in this older test.
Testing at 1,024 x 768 under 3DMark2003 turned the tides, though, with the SLI solution managing a handy lead over both the X800XT and single 6600GT solutions. Ramping up the screen resolution had an even more dramatic effect on this performance gap, with the SLI solution showing up a clear winner in both 3DMark2001 and 3DMark2003 testing at 1,280 x 1,024 pixels, with 4x anti-aliasing and anisotropic filtering enabled.

Gaming tests echoed these results, with the SLI solution managing to maintain its performance as the resolutions were scaled up. Doom 3 saw the SLI setup go from 92fps under 1,024 x 768 to 81.3fps at 1,280 x 1,024, and 66.1fps at 1,600 x 1,200. This contrasts with 77.7, 57.5, and 42.2fps for the single 6600GT and 91.3, 73.3 and 55.4fps for the X800XT.

It’s no secret that Doom 3 favours the Nvidia GPUs, so we also tested under Far Cry 1.3. Here the GeForce 6600GT SLI configuration couldn’t match the performance of the more expensive ATI Radeon X800XT, scoring 64.22fps and 74.36fps respectively. Again, the gap was reduced as the resolution was scaled up, but not as dramatically as in other tests. At 1,600 x 1,200 pixels, the SLI setup dropped 6fps to reach 58.67fps, while the Radeon X800XT dropped 8fps to 66.12fps.

The dual 6600GT configuration was slower than the single card setup at 1,024 x 768 (71.87fps over 64.22fps), but scaling up dramatically turned the tide — the single card could only manage 40.26fps at 1,600 x 1,200. This indicates that the biggest boost will come playing games at high resolutions, but it still falls short of the mark set by Nvidia.

SLI for PENTIUM 4?
At the time of writing, a number of motherboard manufacturers, including Gigabyte, were working on SLI implementations for Pentium 4 boards.

This requires a fairly substantial reworking of the existing board designs to provide a second PCI Express x8 slot on the board to accept a second video card, and is likely to be something of a kludge to get working efficiently. Nvidia potentially has a leg-up here, as the company has been responsible for both the design of the chipset and GPUs, enabling the company to have total control over the design and production process — a system that has served Apple well since the company’s inception. Expect APC to bring you a review with benchmark results as soon as we can get a production model into the labs for testing.

The prohibitive cost does count against this solution. An SLI-compatible motherboard will set you back around $300, and you then have to factor in the cost of two video cards and, in the case of beefy solutions like Nvidia Geforce 6800GTs, a large power supply. Gamers have shown that they are willing to pay for extra performance, so the SLI solution will find a home with the more dedicated frame-rate junkies. But the idea of chasing down two identical video cards and a compatible motherboard will deter most casual users, and those who don’t play games regularly are advised to avoid the technology.

Given that the ATI Radeon X800XT is nipping at the heels of the dual Geforce 6600GT SLI implementation in terms of performance and price, it‘ll be interesting to see how the upcoming ATI Radeon x850 will perform on a dollar-per-frame basis. At present, the performance boost offered by the SLI solution is enough to attract some hard-core gaming enthusiasts and keep sales of Nvidia’s cards ticking over, but it’s a niche solution.

Details

Contact ASUS
Online www.asus.com.au
Price ASUS A8N-SLI Deluxe, Motherboard, $299; ASUS N6600GT Nvidia Geforce, 6600GT, $399 each
Intended market Prosumers

http://www.apcmag.com/apc/v3.nsf/0/6E54C1C28AB650EDCA256FF10005782A

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