How does crossfire work?

2 cards, 1 monitor. Each card basically handles half of the processing, so in theory, you should get twice the frame rates. It doesn't work out quite like that, but it does help a lot. Of course there are a lot of other things to consider, for instance the resolution you run at must be pretty high to see the most benefit, just google, there is a ton of info, literally a ton of it around.

Yep. As stated above both cards run together for output to just a single monitor.

Props for going with the 4870.

so if i have 2 cards i can just stick 1 monitor cable in 1 of the cards?? and it will work fine ?? how how does the computer know how to run 2 cards?

Yes, you can hook up 1 monitor. As a matter of fact, you can only use the output on one card when you use CrossfireX.

There is a Crossfire ribbon that you connect to both cards, and in the drivers you can either enable or disable crossfirex. The drivers is how the computer knows how to run 2 cards. Scaling is getting a lot better than it used to be.

ok thanks for the help guys puts my mind at ease