What exactly does an SLI system mean?

i been seeing this term more and more… what exactly does it mean… is it worth getting on a new system? thanks

Scalable Link Interface (SLI) is a method for linking two (or possibly more) video cards together to produce a single output.

Take a look here

SLI is a new technology developed by NVIDIA in which you can use 2 identical PCI Express video cards to share the graphics load of one task. You need an SLI motherboard with 2 PCI 16x slots and 2 identical SLI compliant video cards. Truthfully, I do not think that it is worth it since cards with dual processors already on them will be comming out soon. If your cosidering it, get dual lower end cards. If you dont…you will be looking at roughly $1000 - $1200 in video cards if you get the best. If you get 2 GeForce 6800 standard SLI cards your looking at roughly $350. This setup will perform just as fast a 6800 ultra, which is $500. The problem is power consumption of the cards and you not only need an SLI Motherboard, but you also need the cards and a beefy computer power supply of 500 watts. All things considered… make an educated decision. ATI has a similar technology to compete with Nvidia also.

Leadtek have released a Dual Core GPU, a 6600 I believe - No 3D Gaming Performance increase was found. Dual Core’s advantages cant be properly utilised by Graphic Processing. Dual GPU Cards again in theory wont boost the performance by alot + cache coherency will then become an issue.

This is most likely not worth it as you could pick up a single 7800GTX for similar money. SLI is only worth it if you plan on getting 2x Vanilla 7800GTX’s. I decided against the 2 6800’s for 1 7800GTX. I’m glad of the SLI M/Board Purchase for future sake though.

I have heard Nvidia will release a new driver which will let the use of two cards not from the same manufacter for example :

Leadtek 6600GT
and a
Xfx 6600GT

Just checked Nvidias site the new driver is out the Version is : 81.85

the benefits as said by manufacture:

Example: You can use a GeForce 7800 GTX from manufacturer ABC with a GeForce 7800 GTX from manufacturer XYZ.
Note: You must still use two graphics cards that have the same GPU. For example, a GeForce 7800 GT must be matched with another GeForce 7800 GT (not with a GeForce 7800 GTX or a GeForce 6800 Ultra).

Mix and Match Graphics Cards with Different Input/Output Ports
Example: You can use a GeForce 6800 GT with Dual DVI & TV-out with a GeForce 6800 GT with Dual DVI & VIVO.

Mix and Match Graphics Cards with Different Clock Speeds
Example: You can use a higher clocked GeForce 6600 GT 550/525 with a standard clock GeForce 6600 GT 500/500.

Mix and Match Graphics Cards with Different Memory Sizes
Example: Using Coolbits, you can use a 128MB GeForce 6800 GT with a 256MB GeForce 6800 GT.

Note: NVIDIA recommends that SLI customers, whenever possible, purchase graphics cards with matching memory sizes. When dissimilar memory sizes are enabled to work together using Coolbits (value set to 18), the effective memory size for each card becomes the smaller of the two memory sizes.