Video memory

[TonyTheNain]

Hello!

 

I was asking myself since 10 minutes: why does in SLI video memory don't stack?

 

Answers anyone? Thank ya!

[don_svetlio]

Because each GPU needs to store the same data so as to actually work

[oaml yya]

This is normal, as graphics cards in sli run 'together but independently'. Each graphics card will run an instance of the game to synchronize with each other, thus it will use equal amount of video memory on each card.

[EunSoo]

 

Quote

Because Crossfire / SLI isn't an efficient way of using two cards simultaneously.

From what I understand, the two cards copy or mirror the vram so they can synchronise with one another. 

There is a simplified explanation. If calculation that are being rendered in GPU2, the variable needs to passed back to GPU1 in the same video memory location. If both video cards have independent memory management there will be situations where it will accidentally overwrite the data when exchanging data.

A solution could be for GPU2 to store data in the main memory, then GPU1 can fetch the data from the main memory. GPU2 would need to know the exact location to extract the data, but this way of buffering is inefficient and would cause delays in fetching and potentially reducing the frame rate, thus defeating the purpose of CF or SLI.

Unlike physical dual GPU cards i.e. 4870X2 which have two GPUs on the PCB, they are more efficient in respect that there would be schedulers and reserve buffer memory to store and synchronise data so the data does corrupt or overwrite one another.

www.techpowerup.com/forums/threads/why-cant-crossfire-or-sli-use-the-sum-of-vram-from-all-gpus.167301/

[TonyTheNain]

Oh ok i understand now. Thank you

[Matias_Chambers]

When Pascal comes,VRAM will be stackable. 

[incarnate]

2 minutes ago, Matias_Chambers said:

When Pascal comes,VRAM will be stackable. 

Source?

[Matias_Chambers]

2 minutes ago, incarnate said:

Source?

http://wccftech.com/nvidia-pascal-gtx-1080-8gb-1070-launching-summer-debut-april-gtc-2016/

[incarnate]

33 minutes ago, Matias_Chambers said:

http://wccftech.com/nvidia-pascal-gtx-1080-8gb-1070-launching-summer-debut-april-gtc-2016/

Wccf is hardly known for its credibility. Seeing as how I haven't seen anything from other sources, I'm going to take that article with a huge grain of salt. So should everyone.

[BrightCandle]

1 hour ago, Matias_Chambers said:

When Pascal comes,VRAM will be stackable. 

Its possible to do that today with DX11 and DX12 but it requires game support and none of them do support it. Even with SLI/Crossfire today being a simple enough matter of limiting your use of previous images we are still having issues with AFR in games made today. People are imagining a world in the future where somehow games developers do much more when today they barely do the absolutely minimum and its actually Nvidia and AMD that fix all the issues?! Its not going to happen, anything that requires game developers to support it for a small niche of performance users is only going to happen in a very small set of games.

[Citadelen]

1 hour ago, Matias_Chambers said:

When Pascal comes,VRAM will be stackable. 

VRAM is already stackable with DX12.