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Does memory stack in SLi/CFX aswell as dual gpus?

post #1 of 7
Thread Starter 
Uh, me and a friend are having a debate and then I asked coffeejunkie.
Quote:
Johnny Guitar: I need to settle a debate
Johnny Guitar: if you have a dual gpu
Johnny Guitar: like the 6990
[GM] coffeejunky: yes
Johnny Guitar: is all the ram accesable
Johnny Guitar: or only 2gb
[GM] coffeejunky: When crossfire is supported the full 4GB will be usable
[GM] coffeejunky: if the game does not support crossfire it will only use 1 GPU's worth of memory (i.e. 2GB)
Johnny Guitar: wait so if a game supports SLi I get 3gb with my 580s?
[GM] coffeejunky: yes
I've never heard of this, is it true?
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I love Corsair
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post #2 of 7
The "friend" being me, If I'm wrong I concede default and will have learned something today.
post #3 of 7
If you have 4 gigs like the 6990, only 2 gigs is being effectively used.
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post #4 of 7
Take alternate frame rendering for example, they're alternating every other frame but it's the same instance and same textures. Each card is basically working as a single unit, and you only get 2GB effective memory.
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post #5 of 7
Only the amount of memory per card is used (if you have 2 1GB 460s only 1GB is going to be usable by SLI). Each card takes in the same data and processes only certain frames of that data (one card does odd frames and one does evens).
post #6 of 7
The process is split between the gpus using ONLY the 1ry gpu's memory.
So 6990 has 2g of "usable" memory. As they cant xfire 2g and 1g cards since then it will address the lower value (1g).
So sli gtx 580 is still 1.5g. 2 gtx 460 (1g) uses 1g...etc
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The bottleneck
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post #7 of 7
Dude is wrong. Hit the SLI/CFX FAQ.
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