crossfire 4890 1g ddr5 with 4850 512 ddr3

[fazlollah]

hi guys
i was wondering if i can run my two video cards in crossfire mode .
some says that if you crossfire these two cards, the 4890 will be downclocked to 4850 !
is this true ?
i have a p5kpl_1600 asus motherboard with q6600 cpu _ 535 green psu and 4gb ddr2 ram
my motherboard has a blue 16x pci express and a black 16x pci express. i heard if i place the 4890 in the main slot ( i assume its the blue one ! ), it will not affect any downclock on my 4890.

plz help me guys ! i need some advice !

 

[cdrkf]

*if* the 2 cards will crossfire (and that is a big if) then the 2 cards must run with equal settings due to how it works. On that basis, you're 4890 will drop it's clocks to the speed of the 4850, and also you'll be limited to the 512mb of ram on the weaker card (as the memory is duplicated on both cards). Depending on what game you're going to play you might get a speed boost, but you'll probably find you're better off just using the 4890.

As a side note you can probably get a much faster single card than those in crossfire anyway, the 4000 series was good in it's day but it's really out of date now!

 

[fazlollah]

but i heard that matching clock speed is for sli mode !
if in crossfire mode, clock speeds gonna be equal, what is the use of crossfiring two cards with different models ?

 

[cdrkf]

but i heard that matching clock speed is for sli mode !
if in crossfire mode, clock speeds gonna be equal, what is the use of crossfiring two cards with different models ?

SLI = Nvidia, Crossfire = AMD / ATI cards. What they do is effectively the same thing.

The way it works in either, is that each card renders a frame alternately- so in theory if you add 2 cards together you can double the frame rate (as one card outputs a frame whilst the other is rendering the next).

Putting mismatched cards together causes problems as one card will finish the frames faster than the other leading to stuttering (which can be a problem anyway with dual cards).

 

[fazlollah]

hmm
so you say the core clock on my 4890 should reduce from 850 to 650 in order to fix this problem !
what if i overclock my 4850 to 850 mhz ?

 

[cdrkf]

hmm
so you say the core clock on my 4890 should reduce from 850 to 650 in order to fix this problem !
what if i overclock my 4850 to 850 mhz ?

It might work- if the card will take it. I'm not sure the 4890 and 4850 will actually work together though. I guess all you can do is fit both cards and see if you can enable crossfire...

 

[fazlollah]

tnks dude

 

[Murissokah]

but i heard that matching clock speed is for sli mode !
if in crossfire mode, clock speeds gonna be equal, what is the use of crossfiring two cards with different models ?

SLI = Nvidia, Crossfire = AMD / ATI cards. What they do is effectively the same thing.

Not entirely true, one of the differences being exactly the fact that Crossfire supports different frequency settings among the cards. See below for reference:

http://hardforum.com/showthread.php?t=1528111

You can match your cards and they can work each with their own clock settings. What may happen is CCC (catalyst) tries to set them to the same clocks. If that happens, you can manually adjust them back.

Having the cards running at different clock speeds will net you more frames (as opposed to both at the lower settings), although I'd expect some crazy latency in highly demanding scenarios.

My advice is to set them up with different settings and try it out.

 

[cdrkf]

but i heard that matching clock speed is for sli mode !
if in crossfire mode, clock speeds gonna be equal, what is the use of crossfiring two cards with different models ?

SLI = Nvidia, Crossfire = AMD / ATI cards. What they do is effectively the same thing.

Not entirely true, one of the differences being exactly the fact that Crossfire supports different frequency settings among the cards. See below for reference:

http://hardforum.com/showthread.php?t=1528111

You can match your cards and they can work each with their own clock settings. What may happen is CCC (catalyst) tries to set them to the same clocks. If that happens, you can manually adjust them back.

Having the cards running at different clock speeds will net you more frames (as opposed to both at the lower settings), although I'd expect some crazy latency in highly demanding scenarios.

My advice is to set them up with different settings and try it out.

Ah thanks, I knew AMD cards supported 'asymmetric' crossfire with their APU's, but I wasn't sure about discreet.