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Why doesn't your VRAM increase in crossfire/SLI?

sli crossfire gpu vram

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#1 KamiQueso

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Posted 04 January 2014 - 04:44 AM

Sorry if this is a noob question, but after watching Linus' videos for quite some time I've learned that your VRAM stays the same as one videocard in Crossfire or SLI. Why does this occur? If you run two 3gig cards in SLI,  how come you  don't have 6gigs of VRAM and what happens to the 3 other gigs of memory?

 

Again, sorry if this is a stupid question but I've wondered about this for a long time.



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#2 M-ursu

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Posted 04 January 2014 - 04:48 AM

Both GPU's need to have theyr own memory, they cant share it.


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#3 mineblaster

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Posted 04 January 2014 - 04:51 AM

because they are like painters all working on the same picture the but when you add video cards its like hire more workers but the picture dose not get bigger


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#4 killcomic

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Posted 04 January 2014 - 04:52 AM

What the above post said. Both cards are being used to render the same scene. So for example, the exact same textures are loaded in duplicate on both cards, so 2x3Gb cards will still be holding 3Gb worth of info because it is duplicated.


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#5 Thunderjolt

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Posted 04 January 2014 - 04:53 AM

Because for the GPU to do work it needs to have the files loaded onto it. Since they can't share resources they both need the same files loaded onto them.


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#6 Panda of the Shadow

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Posted 04 January 2014 - 04:55 AM

They don't fuse they are still two cards. They work together but they aren't the same card. One does one frame one progresses another.



#7 Giggitygoebbels

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Posted 04 January 2014 - 04:59 AM

The VRAM acts like "RAID 1" when in sli/cfx,not "RAID 0".


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#8 lufihengr

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Posted 04 January 2014 - 05:00 AM

They process the same amount of data as one card would, but faster and thus more FPS.


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#9 KamiQueso

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Posted 04 January 2014 - 05:24 AM

Thanks everyone!



#10 NRG

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Posted 04 January 2014 - 11:28 AM

The communication overhead involved in moving data between the vram of multiple cards (among other things) would result in less performance than a single card.


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#11 kevinheinrich

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Posted 04 January 2014 - 11:33 AM

If a programmer finds out how to develop a 3rd party utility/driver to multiply your vram in sli/cfire  Over the course of 24hrs he/she will become richer than the person who invented angry birds.



#12 Panda of the Shadow

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Posted 02 February 2014 - 10:14 AM

If a programmer finds out how to develop a 3rd party utility/driver to multiply your vram in sli/cfire  Over the course of 24hrs he/she will become richer than the person who invented angry birds.

Haha no. 



#13 Aniallation

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Posted 02 February 2014 - 01:01 PM

It would be a lot of work for one GPU to have to pull info from the VRAM of the other, which would require processing through the slots, PCIe bridge, controller, other card, etc. so in the end it's just faster for the card to deal with its own VRAM if it's possible.


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#14 MightyUnit

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Posted 02 February 2014 - 10:42 PM

OP the answer to your question is an understanding of AFR (Alternate Frame Rendering). Each GPU in a SLI or Xire setup takes turns rendering frames. ie: GPU 0 renders frame 1, meanwhile GPU 1 renders frame 2, GPU 0 renders frame 3 and so one. Each frame in stored in the vram of the card that rendered it. So you can see that both cards are not working together on each frame and are NOT sharing vram. Does that make sense??







Also tagged with one or more of these keywords: sli, crossfire, gpu, vram

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