X-bit labs

NVIDIA Multi-GPU SLI Technology: New Approach to Old Ideas (page 38)

Category: Video

by Alexey Stepin , Yaroslav Lyssenko, Anton Shilov

[ 02/25/2005 | 02:15 PM ]

Price Factor

There’s one more important aspect about computer systems with several graphics processors/cards which is the main hindrance for such systems to become widespread and popular among ordinary users. That’s price, of course. Let’s calculate what money the highest-performing version of the nForce4 SLI platform may cost you. Suppose you already have a CPU for Socket 939 and two PC3200 memory modules, and a high-wattage PSU. You need a SLI-compatible mainboard and two SLI-specified graphics cards on NVIDIA’s GPUs.

The ASUS A8N-SLI (ordinary or Deluxe version) will cost you about $200. A PCI Express version of the GeForce 6800 Ultra is priced at $500. A pair of less expensive GeForce 6800 GT cards is going to cost $400 per item, according to NVIDIA. So you’re going to have to pay as much as $800-1000 for the graphics cards only. And these are the best prices since many resellers are selling the GeForce 6800 Ultra for a price high above the recommended one. The total cost of such a computer would be approaching the $4000-5000 mark, which is too high for a home gaming system, even of a highest class. Anyway, this platform will find its client as people who are not limited in money can go for such a purchase. If some game doesn’t work in the SLI mode, you can always switch to the Single-GPU rendering mode and have the performance of a single GeForce 6800 Ultra.

It’s different with the two GeForce 6600 GT. A pair of these cards will cost about $400, without the cost of the mainboard. This seems to be quite affordable for many gamers. At first sight one may think that two GeForce 6600 GT cards are equivalent of the GeForce 6800 Ultra and the RADEON X850 XT Platinum Edition in terms of the number of pixel and vertex processors as well as the amount of graphics memory. But simple arithmetic doesn’t work here – one and one is not necessarily two.

The problem is that besides the synchronization overhead and the lack of support of some games, the amount of graphics memory of two GeForce 6600 GT cards will remain 128MB, rather than 256MB, since the cards in the SLI mode have identical memory contents. This memory size isn’t appropriate for a high-performance solution intended for high resolutions and full-screen antialiasing. The results of our tests confirm this point: the GeForce 6600 GT SLI configuration would be slower in some cases than the single GeForce 6800 Ultra or RADEON X850 XT Platinum Edition or X800 XT with enabled FSAA and aniso-filtering. High resolutions became inaccessible at all in Rome: Total War and 3DMark05 due to the lack of the graphics memory.

That said, we don’t think it’s profitable to purchase two GeForce 6600 GT cards to unite them into a SLI graphics array. You can buy a GeForce 6800 GT or a RADEON X850 XT for about the same money and have the same performance, but without those problems about the compatibility and the amount of the graphics memory.