Down Sides to nVidia's SLI
While nVidia's PCI Express SLI technology sounds great on paper, there are a few down sides we need to mention.
- Server class only?
At this stage it seems like the only way you'll be able to experience nVidia SLI is by buying a server class motherboard, based on the Intel Tumwater. From what we were told, the Tumwater is currently the only chipset to support dual PCI Express 16x slots.
If and only until PCI Express SLI becomes popular at a semi-mainstream level, don't expect to see too many chipset makers produce desktop chipsets with dual PCI Express 16x slot support. On the other hand, it seems highly feasible that nVidia would support dual PCI Express 16x slots in their upcoming nForce desktop chipsets to help move more of their VGA product. Unless ATI turns around and creates their own SLI technology, don't expect the Canadian firm to create support for dual PCI Express 16x in any of their upcoming chipsets.
- Power Hungry
The minimum power supply recommendation for a single GeForce 6800 Ultra system is 350 watt, double that then you have 700 watt. The recommended power supply if you intend on overclocking your system with for a single GeForce 6800 Ultra system is 500 watt, double that then you have 1000 watt.
Let's say you need 200 watts per card, you then have a total of 400 watts for the duo. Add an extra 200 watts or so for the rest of the system, you're at around 600 watts - at a minimum. The math speaks for itself here. If you are intending on using nVidia SLI, keep in mind the type of power supply you'll need and the associated costs which are involved with such a project. Everything starts to make sense now after seeing several 800 watt power supplies while walking around the halls at Computex in Taiwan earlier this month.
- Extreme Performance = Extreme Cost
With Extreme Performance SLI comes Extreme Cost. We did some quick checks on PSU, the graphics cards and server motherboard. For these three components, you're looking at around $2,300 US (roughly $3,300 AU) without even considering other parts of the system, such as the expensive Intel Xeon processor to go along with the Tumwater motherboard.
At the early stages, be prepared to reach deep into your pockets if you want SLI technology in your personal computer. As SLI becomes more popular and the demand for higher capacity power supplies, etc become more widespread, it will eventually help reduce the price and increase the affordability of PCI Express SLI in general.
- Mixing of Cards
One question we quickly had answered by nVidia was whether or not we could mix and match graphics cards. The short answer is, no. You need to be running the exact same graphics card for SLI to work properly.
If you're into overclocking, it was even suggested you overclock both cards at the exact same clock speeds to be safe. The down side to this could be if you have one card which overclocks very well and another which only has mediocre overclocking performance, you will need to adjust both cards clock speeds to the lowest common denominator.
Mixing both ATI and nVidia cards under SLI was laughed off fairly quickly during our press conference in Sydney but it would be rather interesting if someone figured out how to hack SLI to mix ATI and nVidia cards together.
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