How do you Crossfire?

[Broncos]

I have a Radeon HD 4850 512MB 256-bit GDDR3 video card and wanted to upgrade by crossfire. When you add another card to crossfire do you have to have the same 4850 or can you do 4870? and if you have to have a 4850 do you have the have the same amount of memory on the card or can you get a 1g 4850.

Anything you can explain about crossfiring would be very helpful. Thank you very much in advance.

 

[Broncos]

Oh and also does the card memory have to be the same type when you do a crossfire? The video care I'm using now is GDDR3 512MB and the new one I'm thinking about buying to crossfire with is memory type DDR3 1GB.

 

[ewood]

the cards can be different brands. if one is a 512 and one a 1gig both will act as 512mb. as for clocks im pretty sure the faster one clocks down to the clock of the slower one. ive heard people say that if you put the faster one in the primary slot it could help performance because the primary card handles the calculations crossfire entails (syncing data and stuff). a 4870 and 4850 would work but the 4870 wouldnt run at its full potential.
It would be great if someone could clear up the stronger card in the primary slot bit...

 

[jennyh]

You can combine a 4850 with a 4870 in crossfire, but both will behave like the slowest card, in this case the 4850. I'm not sure about that primary slot thing but it would make sense to have your fastest card in that slot anyway, though both will change to 8x8x anyway unless you have an fx mobo.

Same with memory, if one has 1gb and one has 512mb, both will act like they have 512mb.