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4890 crossfired with 4870

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April 9, 2009 4:46:10 PM

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.

More about : 4890 crossfired 4870

April 9, 2009 4:59:27 PM

Read the FAQ at the top of the front page!
Also check the ATI site to make sure your MB will work with CFX.
And you`ll need plenty of power.
April 9, 2009 4:59:29 PM

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.
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April 9, 2009 5:59:17 PM

rangers said:
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.


ah! That's very good to know! The 4870 still looks to be a good buy and the two together should preform well, I would think
April 9, 2009 6:31:01 PM

Quote:
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.



I'm aware of all the requirements and all of my parts are compatible my current setup is

Gigabyte GA-EX58-UD5
Intel Core i7 920
Cosair CMPSU-750TX
ATI 4890
3x2gigs gskill DDR3 1600 memory

Everything matches with ATI's system requirements.. except the chart on ATI's website needs to be updated (the one here http://ati.amd.com/technology/crossfire/charts.html) and asking here is my research lol. But thanks for the tips though, i'm going to give ATI customer service a call
April 9, 2009 6:57:02 PM

Quote:
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
April 9, 2009 8:07:54 PM

Actually, from what I know, is that the faster card will be bottleneck by the slower card if they both are crossfired. The speed of the faster card will be lowered to the slower card's speed if they both are crossfired. Unlike SLI, crossfire will allow us to use 2 different card models together but still, at the end it would make more sense to crossfire 2 same card models together. It would be better to crossfire HD 4870 with another HD 4870 unless if HD 4890 is cheaper. Also, 2 same card models would scale better than using 2 different card models together.
April 9, 2009 8:11:02 PM

rangers said:
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

April 10, 2009 1:50:15 PM

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
April 10, 2009 2:53:22 PM

from what i remember the faster card was downclocked, but seem to remember that they changed that but im not a 100%.


most of the time tech support don't know there @ss from there elbow, maybe TGGA can come in with the answer, i would like to know myself
April 10, 2009 3:11:30 PM

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/messageview.aspx?FTVAR_FORU...

seems to suggest different clocks
April 10, 2009 3:15:02 PM

if you read all the posts you see that they keep there different clocks
April 10, 2009 3:19:59 PM

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

Mactronix
April 10, 2009 3:22:34 PM

crossfires crossfire mate
September 22, 2009 12:38:29 AM

Hey guys I know im a little late answering this thread but I just bumped into it then. I have a gigabyte 4890 OC edition and a reference sapphire 4870. Both are crossfired and the 4890 does not down clock to the 4870 clocks. In fact I have both clocked to 1100Mhz memory and the 4890 @ 955mhz core and the 4870@ 810mhz core.
September 23, 2009 3:03:22 AM

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.
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