Really dumb dual GPU question.

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checkitman22

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With the release of the MARS II I had a really stupid question.

I know when you have two cards in SLI and they are both 1GB you only have 1GB of effective memory, not 2GB.

So, this is why I'm confused.

The GTX 590 and Mars II are marketed as 3GB, but there "are" GTX 580s that are 3GB. So is the GTX 590 really 1.5GB of effective memory (1.5GB per chip), or is it 3GB per chip? Or does any of that even come into account because the card is on one PCB.

The same goes for the 6990 being 4GB. I don't get how they can market it as 4GB, it really IS 2GB of effective memory right?

 
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It's basicly just 2 GPU's on the same PCB.Each has their own but in retrospect when you look at it as a single card you could say it has the combined amount.Even though each GPU only as 2G or 1.5G.The GTX590's are complete reference so they only have 1.5G each.I doubt you will find a GTX590 that has 6G.
It's basicly just 2 GPU's on the same PCB.Each has their own but in retrospect when you look at it as a single card you could say it has the combined amount.Even though each GPU only as 2G or 1.5G.The GTX590's are complete reference so they only have 1.5G each.I doubt you will find a GTX590 that has 6G.
 
Solution
Effective memory is the amount of memory a GPU can actually use. A dual GPU card may be marketed with 3 or 4GB of memory however that will be split between two GPUs. Each GPU can only use half of the total memory on the card because of the way SLI/Crossfire works. The data to be processed by the GPUs is copied to both GPUs and their allotted memory. Neither GPU can take memory from the other if it needs more. So while the card says you may have 3 or 4 GB of memory, you have to remember that the usable amount is only going to be half of that.
 

checkitman22

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Thank you everyone. This what I already thought, and was sure I knew. But I was trying to explain to my friend that it was better to get two GTX 580 3GBs and SLI them than to get a MARS, he was trying to explain to me how "cost aside" the MARS would be better. Then the question about memory came up, I thought I was right, but I needed to make sure.

EDIT - For the price (and size) of the MARS it would have been nice to see it with 6GB, it would make sense in my opinion, but meh what ever. It is what it is.
 
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