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Crossfire - i need advice >.<

Last response: in Graphics & Displays
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December 25, 2008 9:31:20 AM

Hi peepsIve currently got an overclocked hd4870 512mb   and im looking to crossfire it with another hd4870. Ive got my eyes on a palit hd4870 1GB for 180quid.  Im unsure about how they will perform together as 1 is 512mb and the other is 1gb.  Im i right in thinking that the 1GB card will only be able to use 512mb because the other card is only 512mb, or will i get 1.5gb (1gb+512mb)?there is very little price difference between a 512mb and a 1gb card  soo i thought it would be worth getting the 1GB card if it will perform at 1GB.i dnt have any experience with Crossfire or SLi   so any advice/help would be much appreciated.  Thanks in advance.(also will my C2D E8400 @ 3.8ghz be able to keep up with 2 hd4870's?  )

More about : crossfire advice

December 25, 2008 1:17:49 PM

What resolution are you running at?
Both cards will be cut down to 512MB of video memory. Make sure you're power supply can handle them.
Also, you're processor is fine.
a b U Graphics card
December 25, 2008 1:56:32 PM

Buy another 512meg card.
The extra 512 meg will not be used on the 1 gig card.
Both cards will run at the specs of the lowest clocked card.
Your best bet is to buy another exactly like the one you have.
Your processor is fine for Crossfiring a couple of 4870's.
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December 25, 2008 1:56:42 PM

ok thanks alot, thats really helpful.
im using my 32inch toshiba tv as a monitor with a max resolution of 1920x1080

Do you think it is worth getting another hd4870 or would it be better if i sold my current 4870 and brought a hd4870x2?

Is there much difference between 2x hd4870s (both 512mb) in Xfire and a 4870x2 i know the x2 has 2gb of memory but i dnt think any games use more than 1gb of video memory, but thats just my guess.

My PSU is a coolermaster real power m700 (M=modular and 700 is for 700watts).
December 25, 2008 2:04:49 PM

With Crossfire you need to remember that when you connect the cards it does not combine the memory only the GPU's work together. So if you have a 512mb card and Crossfire it to a second 512mb card your total avalible memory is still only 512mb.

You can Crossfire the 1Gb card with the 512mb card and if you do it right have 1Gb of total combined video memory. To do this the 1Gb card has to be the master (the card with your monitor connected to it) and the 512mb card just used for its GPU.

Also you need to remember that if you have two cards with different core clock speeds and memory speeds Crossfire will default to the slower speed of the two. So keep that in mind when looking for your second card.
December 25, 2008 2:05:36 PM

oh i have another very important question
my mobo is a asus p5q-e and it has 1 16x pci-e lane and 1 8x pci-e lane, when you put to cards in crossfire on this board both lanes run at 8x, is this enough for a 4870 to run at full speed or does it need 16x ?

any help would be much appreiated :D 
a b U Graphics card
December 25, 2008 2:36:54 PM

I have never heard of a way you can set them up so that all the memory is used from 1 card, and the other is simply used a an extra processor.....my understanding, as well as input on the ATI Crossfire forums is that each card will use, and be limited to the amount of memory on the lessor card.
So no matter how you install them, each card will use 512 meg of memory.
And no, the memory is not "combined".
2 512 meg cards in Crossfire will report 512 meg of total video memory.
Now the memory may be reported as 1 gig if you set the 1 gig card to master, but still, the cards will each be able to use only 512meg of their own memory while Crossfire is enabled.
December 25, 2008 2:44:03 PM

so effectily i will get 1gb of video memory?(512mb + 512mb) or just 512mb? im so confussed now:S
if all i will get is 512mb of video memory then i wont bother its just not worth 370 quid
i might aswell try and sell my hd4870 and save up for a hd4870x2

i r so confussed can someone clear things up ?!?
December 25, 2008 2:46:27 PM

(p.s merry x-mas!!! :D :D :D :D )
December 25, 2008 2:47:25 PM

If your board only has one 16X and one 8X lane your going to take a hit since both lanes will run at 8X under Crossfire. You best bet with a board like that is to get a 4870X2 and just use the 16X slot.
December 25, 2008 2:50:31 PM

ok thanks
my friend told me that a hd4870 wont use half of a 16x lane but i have a plan (muhahaha)

ill stick my hd4870 in the 8x lane later and run 3dmark06 and see how much differance there is
man i wish i had a better paid job =/ =/
December 25, 2008 3:04:43 PM

Will be interesting to see what the difference shows up to be.
December 25, 2008 3:06:34 PM

yep gonna change it now
my 3dmark06 score is 15500 roughly (16x lane) be back in 10 to tell you the results
a b U Graphics card
December 25, 2008 3:20:40 PM

The cards will each use 512 meg of memory. But it is not combined. You do not have 1 gig effective total, you have 2 cards each using 512meg.
December 25, 2008 4:07:06 PM

ok thanks for clearing that up.
well i changed my card to a 8x lane and it ran 3dmark06 fine until the last test where i got artifacts all over my screen and my rig rebooted =/ but up intil that point it was running as fast as it usually does (the crash my have something to do with my cpu OC or my GPU OC its at 790/1100, which is the max on CCC but my temps are still good at about 65C under load)

anyways ive decided to sell it and go for a 4870x2 as it is the tits :D 

thanks guys for ur helpful info and advice
!