Crossfire with 4890 and 4870 worth it?

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Dan UCF

[H]ard|Gawd
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I have a 4870 and want to get a second card for Crossfire. I would much rather get a 4890 for my second card if possible since it is almost the exact same price as my 4870. Anyone have experience and/or suggestions?
 
Wow, I sooo did not know it was possible to do this but if an HD 4870 and HD 4850 can be crossfired then I'd assume an HD 4890 and HD 4870 can be.

Just googled and found out an HD 4870 and HD 4850 can be crossfired o_O

I guess it kinda makes sense as its the GPU's doing the work and only the mem from one card gets used I believe but if your HD 4870 is a 512mb card it may lock down 512mb of the HD 4890 while in xfire.
 
Don't think this is wise. As far as I remember, you'll then limit the 4890 to the same clock speeds as the 4870, meaning using the 4890's OC'ing potential is out of the picture.

Think it'd be a better option to sell the 4870 and just use a single 4890 which you'll then OC; you'll probably see nearly as good performance, and you won't have to worry about potential CF issues with games and such.
 
Raap said:
Don't think this is wise. As far as I remember, you'll then limit the 4890 to the same clock speeds as the 4870, meaning using the 4890's OC'ing potential is out of the picture.

Think it'd be a better option to sell the 4870 and just use a single 4890 which you'll then OC; you'll probably see nearly as good performance, and you won't have to worry about potential CF issues with games and such.
Click to expand...

There would be no "issues" with crossfire, it'd simply be like normal HD 4870 xfire unless you find the max OC of the HD 4870 and bios mod it which if you can get the 850/975 of the HD 4890 its the same as having HD 4890 xfire as the HD4890 won't have to slow itself down :)
 
Jumping jeebus how long is this misinformation going to circulate? People have been claiming incorrectly that Crossfire "downclocks" faster cards since I used X1900XT Crossfire.

Crossfire has always ran async, or that is that cards do not have to be the same speed. A faster card will not have its clock reduced.

What a person wouldn't want to do is match a 512Mb card with a 1Gb card because your effective ram would be dropped to 512Mb.
 
Blacklash said:
Jumping jeebus how long is this misinformation going to circulate? People have been claiming incorrectly that Crossfire "downclocks" faster cards since I used X1900XT Crossfire.

Crossfire has always ran async, or that is that cards do not have to be the same speed. A faster card will not have its clock reduced.
Click to expand...

The way I understood it, the faster card will indeed not be 'downclocked', i.e. you can't see in CCC that the card is running at a lower speed. However, it will *perform* like the other card when you run a CF-enabled game. So mix a 4890 and a 4870, and you effectively end up with two 4870's.

Are you saying this isn't the case?

I suppose it could be tested easily enough by first running a benchmark with both cards at stock speed, and then running another benchmark after clocking down the faster card to the same clocks as the slower one.

*edit*

Found it. Have a look here: http://ati.amd.com/technology/crossfire/faq.html

5. What happens when graphics cards with varying memory speeds and engine clocks are paired together?

A. In this scenario, overall performance will be adjusted to match the memory speeds and engine clocks of the lower clocked card. To obtain ideal performance, graphics cards should be paired correctly.
Click to expand...
 
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For shits and giggles I'ma try to crossfire a 4670 with my 4850 when I get home tonight :) Seriously though, I am. We have an HIS 4670 at work and I'ma try it >: P
 
Blacklash said:
Jumping jeebus how long is this misinformation going to circulate? People have been claiming incorrectly that Crossfire "downclocks" faster cards since I used X1900XT Crossfire.

Crossfire has always ran async, or that is that cards do not have to be the same speed. A faster card will not have its clock reduced.

What a person wouldn't want to do is match a 512Mb card with a 1Gb card because your effective ram would be dropped to 512Mb.
Click to expand...

As pointed out, it isnt miss-information, but you who is miss-informed.
 
x1800xl and an x1800 cf card (clocked the same as an xt) would run at the speed of the xl. x1900xt has the same clocks as the x1900 cf card, but if you had an x1900xtx card you wouldn't see any faster performance than if you had an xt.
 
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