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Can I do crossfire with a 6870 and a 6850?

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January 3, 2012 3:52:48 PM

I have recently bought a new 6870. Can I buy a 6850 and crossfire it with my 6870? How will they perform? Will they perform like 6850 crossfire or 6870 crossfire? Do you recommend it or should I buy another 6870 instead of the 6850?

More about : crossfire 6870 6850

a c 175 U Graphics card
January 3, 2012 4:00:55 PM

[ignore]
January 3, 2012 4:03:45 PM

I have, that is only 6850 and 6870 crossfire, not those together.
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a c 175 U Graphics card
January 3, 2012 4:19:40 PM

Oh! Sorry! My mistake, I wasn't checking down!

Better go for another 6870, it's not that more expensive...
January 3, 2012 4:25:10 PM

Ok :)  Then I will do that
a c 80 U Graphics card
January 3, 2012 4:25:37 PM

yes, you can cfx a 6850 and a 6870 because they both belong to the 68xx series. the 6870 will match the 6850's speed and run as 2x 6750s in cfx. for better performance, cfx a 6870 1 gb gddr5 with a 6870 1 gb gddr5 (memory doesn't double in cfx/sli).
January 3, 2012 4:28:45 PM

As far as I know having a 6850 and 6870 in crossfire will cause you to get the same performance as 2x 6850.

While 2x 6850 is significantly better than 1x 6870, I'd much rather you get another 6870.

Dual 6870's are pretty formidable.

To answer your OP, yes you can Crossfire them if your motherboard has crossfire support.

Could you list your specs and playing resolution please?

Thank you.
January 3, 2012 4:31:44 PM

the 6870 would underclock itself to match 6850 speeds. crossfired 6850's is good, but it's a total waste of a 6870
January 3, 2012 5:55:17 PM

internetswag said:
As far as I know having a 6850 and 6870 in crossfire will cause you to get the same performance as 2x 6850.

While 2x 6850 is significantly better than 1x 6870, I'd much rather you get another 6870.

Dual 6870's are pretty formidable.

To answer your OP, yes you can Crossfire them if your motherboard has crossfire support.

Could you list your specs and playing resolution please?

Thank you.



Yes, I have an
AMD 955 @ 4.0 GHz
Silver Power 750Watt Modular
Gigabyte 990XA-UD3 mobo
WD 500GB
Kingston ValueR 1333MHz 2x2gb RAM
Cooler Master HAF X
AMD Radeon 6870
January 4, 2012 11:40:03 AM

From Gigabyte website.

GA-990XA-UD3

Expansion Slots

1 x PCI Express x16 slot, running at x16 (PCIEX16) (Note 3)
1 x PCI Express x16 slot, running at x8 (PCIEX8) (Note 4)
1 x PCI Express x16 slot, running at x4 (PCIEX4)
2 x PCI Express x1 slots
(All PCI Express slots conform to the PCI Express 2.0 standard.)
2 x PCI slots


So one of your PCI-E 16 slots are running at 8x speed and not 16x. I'm not sure how this will impact speed overall especially with a 6870 going Crossfire with a 6850.

You might end up getting the performance of 2x 6850's reduced by about 10%.

But don't hold me to that, I as well would like to know how it'd effect performance. All I can do is make an assumption.

So any other dudes reading this feel free to give some advice. Thanks.
a c 175 U Graphics card
January 4, 2012 11:50:27 AM

A 8x should be fine with 68xx series. It will not really make a performance difference, except you use very high end cards like 6970 or above as far as I know.
a b U Graphics card
January 4, 2012 12:25:32 PM

internetswag said:
From Gigabyte website.

GA-990XA-UD3

Expansion Slots

1 x PCI Express x16 slot, running at x16 (PCIEX16) (Note 3)
1 x PCI Express x16 slot, running at x8 (PCIEX8) (Note 4)
1 x PCI Express x16 slot, running at x4 (PCIEX4)
2 x PCI Express x1 slots
(All PCI Express slots conform to the PCI Express 2.0 standard.)
2 x PCI slots


So one of your PCI-E 16 slots are running at 8x speed and not 16x. I'm not sure how this will impact speed overall especially with a 6870 going Crossfire with a 6850.

You might end up getting the performance of 2x 6850's reduced by about 10%.

But don't hold me to that, I as well would like to know how it'd effect performance. All I can do is make an assumption.

So any other dudes reading this feel free to give some advice. Thanks.



This is pretty standard for any motherboard. My ASUS RAMPAGE III Extreme has 4 pci-e x 16 capable slots. The setup is 16/0/0/0 16/16/0/0 16/8/8/0/ 8/8/8/8. I think if you keep the primary card in the x16 slot and the secondary card in the x 8 slot you will be ok. You also have the crossfire cable allowing communication between the cards if you worried about losing bandwidth by having it in a x8 slot. There is some pretty good info here in regards to pci-e slot bandwidth. These guys say that even the fastest gpu's don't use much more than half of the available pci-e 16 bandwidth but the do not give any benchmarks to prove this.
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