4890 crossfired with 4870

Just got a 4890 and plan to go crossfire and to save some money I was thinking about getting a 4870 to go with it. I was just wondering if anyone had any benchmarks they could point me to or if there's anything I need to know about a setup like this.

I know you can mix cards with crossfire.. but I also heard that the faster card is clocked down to match the slower card and was wondering if this was true as well.

that was the case but not now, the 4890 will not be down clocked it will pick up the slack from the 4870, the way i understand it in a crossfire setup where both cards are the same, one card will do the top half and the other card will render the bottom half, but in a system where one card is faster you would probably get a 60/40 split.

Well your taking advice from a guy who says "the way I understand it...", which is translated to, "I'm not sure but I think". (no disrespect rangers)
You need to read the FAQ and do research on ATI's website or maybe try ATI tech support, I would think they would be the ones to ask.
Before you go spend a bunch of money on something thats not gonna work correctly together and also make sure you have plenty of leftover amps on your power supply.

none taken mate, its been some time since i researched crossfire, but im almost certain that the advice I gave is right

Just ot let you know I called ATI/AMD they told me that the 4890 would be clocked down to meet the 4870, but maybe they're just saying this to get me to buy a more expensive 4890? lol

Nah, I believe them. I was just hoping I could save some money by doing this... maybe I can get another 4890 before the rebate offer ends

Its funny but generally speaking the higher spec card will down clock to the lower one, im kinda playing devils advocate here but i do know of at least one confirmed occasion where the lower card actually clocked up to the higher one. very un comon but it does happen.
Also being nit picky i always thought ATI Crossfire used AFR by default and not split frame or checkerboard, has this changed ?

Mactronix

looked around a bit and found some thing on anand forum


"Catalyst 8.1 correctly identifies the cards. We could see one HD3870 and one HD3850 card and we could access them separately in the Overdrive section. You can overclock them and the driver allowed us to change GPU and memory clocks on each card regardless from the other card's settings. However, this didn't give us much in terms of performance, but we're still pleased to see that you can mix these R670 based cards and set the clocks independantly."


http://forums.anandtech.com/messag [...] id=2152458

seems to suggest different clocks

How did we get from 4890 and 4870 to 3850 and 3870 ?

Mactronix

ok Guys here you go i did some research into this problem

http://support.amd.com/us/kbarticl [...] rCode.aspx

I have the same setup as Kalidae, however, I have a sapphire vapor-x 4890 and a sapphire vapor-x 4870, and both can be clocked independently in overdrive. I had done the research, and found people had success with the combo and their futuremark vantage scores for the 4890-4870 combo was almost the same as the 4890-4890 cores. Installing the cards and installing the catalyst 9.9 software worked perfectly and recognized each card with no errors. It was just like I had 2 4870's installed, but one had higher clock speeds. And for the record, having one 4890 and one 4870 performs significantly better than 2 4870's while playing Crysis.