sli/crossfire combine vram

[emosun]

so we all know that when in crossfire or sli the vram does not combine.

however , i did just have a shower thought. do both cards not combine vram but simply clone the vram? as in.... do both cards have the same information loaded into vram and just alternate the final output?

It seems unlikely that one one card would have data in it's vram and effectively have to send the data down to the second card for processing only to send it back up to the first card for final output.

[Crunchy Dragon]

I guess that would make sense.

 

Similar to RAID 1, in a way?

[-rascal-]

7 minutes ago, emosun said:

so we all know that when in crossfire or sli the vram does not combine.

however , i did just have a shower thought. do both cards not combine vram but simply clone the vram? as in.... do both cards have the same information loaded into vram and just alternate the final output?

It seems unlikely that one one card would have data in it's vram and effectively have to send the data down to the second card for processing only to send it back up to the first card for final output.

 

The data that needs to be processed is duplicated on to each card.

If memory serves, classic Crossfire/SLi has each GPU render a section of the final frame (e.g. Primary card generates the top-half, and second card generates bottom-half).

Now, each GPU generates every other frame (e.g. GPU #1 generates frame #1, GPU #2 generates frame #2, etc, etc).

 

 

[Rainbow Dash]

It's like @Crunchy Dragon said, the vram will work like a raid 1. But if you had SLI in Watch Dogs 2 it will extend the vram amount instead.

[emosun]

3 minutes ago, Crunchy Dragon said:

I guess that would make sense.

 

Similar to RAID 1, in a way?

yeah i suppose.

like you don't get double the vram , but each gpu needs information so technically you still NEED double the vram for each gpu to work.

the reason i thought of this is my old 3870x2. it's a dual gpu card , but the second gpu on the card doesn't have it's own video output , but it does have ram , so i figure it must be using the ram.

[emosun]

4 minutes ago, -rascal- said:

If memory serves, classic Crossfire/SLi has each GPU render a section of the final frame (e.g. Primary card generates the top-half, and second card generates bottom-half).

well my 3870 x2 has crossfire profiles and afr settings. and supposedly the original voodoo2 would do afr or interlaced stuff.

[Crunchy Dragon]

2 minutes ago, emosun said:

yeah i suppose.

like you don't get double the vram , but each gpu needs information so technically you still NEED double the vram for each gpu to work.

the reason i thought of this is my old 3870x2. it's a dual gpu card , but the second gpu on the card doesn't have it's own video output , but it does have ram , so i figure it must be using the ram.

Dual GPU cards are kind of finicky things. You get an SLI/Crossfire setup in half the space at the price of higher temperatures and half the video outputs.

 

One thing that comes to mind is the R9 295X2, that's a dual GPU card that has 8Gb VRAM(4Gb for each GPU) so it would be more logical to have each card have it's own VRAM in a RAID 1 esque system.