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Anyone Seen 3870/4870 Crossfire?

NaughtyGeek

Golden Member
May 3, 2005
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Just wondering if anyone here has come across any write ups on the new hybrid crossfire from ATI. Specifically I'd like to know what improvement you'd get combining a 3870 with a 4870 over just a 4870.
 

JPB

Diamond Member
Jul 4, 2005
4,032
82
91
It has been confirmed by AMD/ATI that the 3800 series and the 4800 series will NOT work in Crossfire together.
 

bryanW1995

Lifer
May 22, 2007
11,139
28
91
actually, what I read is that it's not OFFICIALLY supported but that they SHOULD work together. I know that apoppin is looking to try a 4870 with his 2900xt, and I'm toying with a 4850 (if they ever get a dual slot unit with good cooling to market) to go with my 3870. I'll let you know how it goes for us, though i'm pretty sure that apoppin will have his before I even think about doing it...
 

JPB

Diamond Member
Jul 4, 2005
4,032
82
91
If its true that is.

ATI official

Despite previous reports on the internet that old Radeon 38x0 and new Radeon 48x0 cards will work in Crossfire together, unfortunately this won't happen.

Two senior software guys at ATI has just confirmed that 3800 series in Crossfire with 4800 won't work and that such a configuration is not supported.


You won't be able to match the generations and we are investigating if you will be able to mix cards from 48x0 series. We believe you should, but we won?t jump the gun with this announcement.

Sorry for destroying one cool dream, but you will have to forget about your 38x0 card and swap it for a much faster 48x0 generation.

At the same time, our friend W1zzard from tech power up has confirmed that he couldn't make 3800 and 4800 generation cards work together in XP, but now we know the answer why. It won't work on XP or Vista, simply as it's not supported.
 

Sylvanas

Diamond Member
Jan 20, 2004
3,753
0
0
Originally posted by: bryanW1995
actually, what I read is that it's not OFFICIALLY
From this article

A source close to AMD told us that there will be ?inter-generation compatibility? between the Radeon 3800 and 4850: ?Since they're both DirectX 10.1 parts, there is no reason why those two should not work together. (?) We will probably not qualify this interoperability, but who stops you from trying?"
There is conflicting reports...I guess it's best to wait until we get a few people actually trying this until we will know for sure.
 

bryanW1995

Lifer
May 22, 2007
11,139
28
91
Originally posted by: JPB
If its true that is.

ATI official

Despite previous reports on the internet that old Radeon 38x0 and new Radeon 48x0 cards will work in Crossfire together, unfortunately this won't happen.

Two senior software guys at ATI has just confirmed that 3800 series in Crossfire with 4800 won't work and that such a configuration is not supported.


You won't be able to match the generations and we are investigating if you will be able to mix cards from 48x0 series. We believe you should, but we won?t jump the gun with this announcement.

Sorry for destroying one cool dream, but you will have to forget about your 38x0 card and swap it for a much faster 48x0 generation.

At the same time, our friend W1zzard from tech power up has confirmed that he couldn't make 3800 and 4800 generation cards work together in XP, but now we know the answer why. It won't work on XP or Vista, simply as it's not supported.
anybody have w1zzard's email? I'm pretty confident that if he can't make it work then we're all going to be sol.
 

BigMoosey74

Member
Dec 18, 2007
92
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0
You must not understand what your GPUs do when they xfire with a different card. It is like RAM, the faster one will downclock to the slower one. Even if it did work...WTF would you want to xfire a 4800 with a 3800? You should just go buy two 3800 cards because that is about the best you are going to get....even if it did/does work. When you xfire, at the least, use the same generation...at best, do identical cards.

Edit: Sorry, I have to expand on that. They don't just downclock, the faster card's output gets limited to avoid micro studdering. The 4800, if it does what you think/hope it will do, it would kick out the alternate frames much quicker than the 3800. To correct for that problem, the output is capped to how fast the 3800 completes a frame in order to smoothen the performance.
 

jasonja

Golden Member
Feb 22, 2001
1,864
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This has never worked nor been supported. These are two different families and CF is not supported in that configuration.
 

Sylvanas

Diamond Member
Jan 20, 2004
3,753
0
0
Originally posted by: BigMoosey74
You must not understand what your GPUs do when they xfire with a different card. It is like RAM, the faster one will downclock to the slower one. Even if it did work...WTF would you want to xfire a 4800 with a 3800? You should just go buy two 3800 cards because that is about the best you are going to get....even if it did/does work. When you xfire, at the least, use the same generation...at best, do identical cards.

Edit: Sorry, I have to expand on that. They don't just downclock, the faster card's output gets limited to avoid micro studdering. The 4800, if it does what you think/hope it will do, it would kick out the alternate frames much quicker than the 3800. To correct for that problem, the output is capped to how fast the 3800 completes a frame in order to smoothen the performance.
Not since Catalyst 8.1 Driver. You can Xfire a 3870X2 with a 3850 and they will both run at their own respective clockspeeds, the 3870X2 is not downclocked from 825mhz core to 667 of the 3850. The reason people would want to do this is if they have an existing 3870 they would rather put it to use with a new 4870 instead of getting rid of it- better performance than a single 4870 some would see as a great investment. When you mix and match cards it's the framebuffer that defaults to the lowest common denominator (e.g. 1x 512 card and 1x 256mb card, the 512mb card will resort to a 256mb framebuffer).

Microstuttering is not to do with clockspeed, it is to do with AFR's implementation and time between each frame. Here is an example of a 3850/3870 Crossfire setup performing better than a standalone 3870. Sure, we working with different architectures here so I would not really expect it to work but it would be cool if it could.
 

bryanW1995

Lifer
May 22, 2007
11,139
28
91
got this from w1zzard a little while ago:


yes i tried and it doesnt work. also i tried under vista and it doesnt work either.



if he can't get it to work then I'll just assume that I won't be able to, either...:( damn, I should have asked him about rivatuner 2.10....
 

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