I'm getting a complete new system very soon, I'm just waiting the release of the 9800GX2 to compare it to the ATI X2 and hopefully some some cheaper (non-extreme) 45nm cpu's ;-) by then.
My question :
To run SLI / Crossfire do the cards need to be exactly the same or just the same model?
So do I wait to buy the second card or allready buy it now to be sure to find the same one in 6 months?
Thanks for any comments.
PS I know prices will drop in a fez months etc
they don't have to be exactly the same but they have to be the same model with the same memory amount ex. GTX768+ GTX768, GTS 640+ GTS 640, etc. They don't have to be from the same manufacture either and they don't even have to be running at the same speed as one can be an OC version while the other is not so long as they are the same model. Keep in mind that by default if one runs faster than the other, they will both link up at the slower of the two speeds. You can fix that by using Rivatuner or similar to manually OC both back up to a common higher speed. If you're brave you can also flash the bios of the slower one to that of the faster one and then they will both detect as the same speed so long as the slower card can handle the OC.
For SLI they have to be the same chip and memory amount, but manufacturer is irrelevant (as has been mentioned). You CANNOT, for example, link a GTS G80 (320,640MB) with a GTS G92 (512MB) or GT.
With crossfire it's a bit more flexible. I have crossfired a 3850 512MB with a 3870 and used Catalyst control panel to bring the 3850 up to 750 mhz to reduce the speed difference. I have also crossfired a 256MB 3850 with a 3870 512MB and it worked as well.
It wasn't a requirement to match speeds, as Catalyst control centre will allow you to keep both cards at stock speed, or allow you to overclock both cards. I only matched speeds to keep gameplay at its smoothest.
I would say I probably recommend a dual GPU card for the ultimate in flexibility, as you are not limited to using one or another vendor's motherboard chipset.
The best SLI bang-for-the-buck (IMHO) is 2x8800GTS G92 512MB cards. You are getting GTX type speed from each for less money, but still more $$ than a 3870x2.