SLI's Split Personality NVIDIA and 3Dfx

Asus has been around for 20-years, this success is most likely based on their steadfast loyalty to the PC-Enthusiast in all of us. Today we built a "budget" SLI rig running two Asus N6600GT Extremes based on the NV43 GPU which fully supports their 256MB GDDR3 memory compliment. Mated with an Asus P5ND2-SLI the system can handle any 3D-title and definitely put the fun back in performance.



Many PC-Enthusiasts are unaware Scalable Link Interface is not an entirely new concept nor is it the same as the original technology which was the brainchild of 3dfx nearly ten years ago. Today SLI involves independent GPUs on separate PCBs sharing rendering of the top and bottom half of the screen. Recent SLI also exploits the new PCIe 16x bus more effectively as the new bus has more to offer. The first use of the acronym in the PC world via 3Dfx stood for Scan Line Interleaving in this case each GPU renders alternating scan lines splitting odd and even. In fact SLI was innate to the architecture of 3Dfx's original SST1 chipset, which was originally marketed to Arcade vendors until memory prices dropped. 3Dfx's first GPU to utilize the SLI feature in a PC was their SST96 and their first card to demonstrate that technology was the Voodoo 2. In the photo below we see two 3dfx Voodoo 2 video-cards linked by ribbon cable.



From a manufacturing perspective past and present SLI differ as NVIDIA has chosen to emulate the original 3Dfx SST96 chipset insofar as avoiding multi-GPU integration on a single card which would have allowed the manufacture to eschew any "bridge" or connection between two cards. 3Dfx worked feverishly to incorporate the technology onto a single PCB and achieved this goal with the release of the Voodoo5 5000 / 5500 (PCI and AGP respectively) this was accomplished with their last GPU the VSA-100. Taking this development even further their next card was and in some respects still is, one of the most coveted video-cards ever built. Only 100+ prototypes were ever made and from those revisions only 20+ of those ever worked. As this 3Dfx Voodoo 6000 Retro test reveals the company ultimately integrated four VSA-100 GPUs on a single PCB surpassing (from PCB package standpoint) what has been accomplished today. Below we see one of the few working Voodoo 6000 prototypes rev. 3700A using the HiNT PCI to PCI chip which replaced an Intel solution.



The card above was retro-tested on a Gigabyte GA-7VRX mobo (KT333 chipset) and many of the problems manufacturers face today with respect to multi-GPU architecture and system integration also plagued 3Dfx. Producing a prototype PCB capable of supporting multiple-GPUs and manufacturing that PCB in bulk at a reasonable cost are completely different accomplishments. Today most high end video-cards sporting a solitary GPU require additional current just as the Voodoo5 6000 did. As seen below an ad hoc resolution was found soldering external leads to the PCB which connected to a Molex.



One of the last operational incarnations Voodoo5 6000 prototypes can be seen below. The final version would have resembled our header photo placing the GPUs in parallel to save space. That was the Intel V6 version and it ultimately failed when the Intel PCI - PCI chips experienced instability. Those Voodoo5 6000's outfitted with a HiNT chip were the only working prototypes (to my knowledge). You can tell the card below is most likely a working version because of the external voltage connector.



So why have I reiterated what most original SLI articles already outlined? My comparisons have a purpose, to exemplify how the concept of integrating multi-GPU architecture onto a single PCB is just as much of an obstacle today as it was over six years ago, which in the PC-Industry is an eternity. The Voodoo5 6000 prototype above required a PSU with at least 26A on the 12V rail and given the controversial EPS12V Power Supply Guideline limiting 12V-rails to 18A and requiring they follow split plane topology which requires independent solder point to ensure the 240VA safety limit is observed it's no wonder there are so few multi-GPU graphic-cards today.

Since 3Dfx the first company to resurrect a multi-GPU technology onto a single PCB was Gigabyte with the release of their GV-3D1 next to follow was a 6800GT version the GV-3D1-68GT. Not to be outdone Asus was soon to follow with an architectural marvel in their Extreme N6800GT-DUAL/2DT/512M. Currently SLI technology uses two PCI slots, two cards and requires twice the power. The ramifications compared to the original concept are twice the motherboard/case real-estate, twice the heat, and nearly twice the cost. What then is the best solution short of manufacturers reincarnating a multi-GPU PCB? Introducing our hero the Asus Extreme N6600GT