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ATI CrossfireX uses RAM from both cards?

post #1 of 11
Thread Starter 
Well I wanted to know, because I saw that SLI doesn't use the RAM from both cards, rathermore one card (a while back), not sure how it is now, but does Crossfire use the RAM from both cards? I have a 4870 512mb, and I want to crossfire a 4850 1gb or 512mb or whatever, but I am not sure if it will be worth it if it doesn't use the RAM.
post #2 of 11
I believe that on either SLI/crossfire the ram is simply mirrored.

EDIT: brb with proof
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post #3 of 11
RAM mirrors between cards.

IE, if you had 2x 1 GB card, the memory would be 'populated', but you would have exactly the same thing on each card. Therefore, only effectively only having 1 GB.
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post #4 of 11
CF = VRAM buffer size is limited by GPU with smallest VRAM
post #5 of 11
Quote:
Originally Posted by beers;13834403 
RAM mirrors between cards.

IE, if you had 2x 1 GB card, the memory would be 'populated', but you would have exactly the same thing on each card. Therefore, only effectively only having 1 GB.

Beers is proof! cheers.gif
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post #6 of 11
Thread Starter 
I don't exactly understand how that works (not exactly savvy in this field) but I'm guessing the RAM will be wasted if I had a 512 card as the main card and 1gb as the secondary? (I could mix and match only if I get same or better performance)
post #7 of 11
Essentially.
There isn't enough room to mirror 1 GB worth of data on a 512 MB card. Therefore, only 512 MB of the 1 GB card will be utilized. This data would be mirrored between cards for an effective total of 512 MB.
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post #8 of 11
Thread Starter 
Quote:
Originally Posted by beers View Post
Essentially.
As there isn't enough room to mirror 1 GB worth of data on a 512 MB card. Therefore, only 512 MB of the 1 GB card will be utilized. This data would be mirrored between cards for an effective total of 512 MB.
BASICALLY, the 1gb on the other card won't be used. Right?

But if I use the 4850 1gb as my primary and the 4870 as my secondary, of course the 2 cores will still be used, just I'll have twice as much memory, will that work?

GRAND TOTAL: 1 GB RAM

right?
post #9 of 11
Quote:
Originally Posted by assaulth3ro911 View Post
BASICALLY, the 1gb on the other card won't be used. Right?

But if I use the 4850 1gb as my primary and the 4870 as my secondary, of course the 2 cores will still be used, just I'll have twice as much memory, will that work?

GRAND TOTAL: 1 GB RAM

right?
Nope. No matter what "main card" your RAM is still limited by the card with the lowest quantity. Meaning 512mb effectively.
    
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post #10 of 11
no, lower ram is used. put a 3g 590 with a 1.5g stock 590 = 1.5 used.

regardless of primary cards memory, lower card is always max mem available
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