Nvidia SLI. What amount of memory is it supposed to show?

[khundkar]

I am a noob to SLI. I just bought a rig, second hand, comes with 2 Nvidia 7900GTX cards in sli mode. Cards are 512 mb each. So thats a total size of 1 gig video memory, yet in windows, it tells me that I have 512mb of video memory. I do get the icon saying sli is enabled.

3dmark does the same thing. It gives 512mb memory.

So my question is, is that normal? Is it only supposed to show 512mb memory
in sli? How do I test if SLI is really working?

Thank you for the help guys.

 

[prozac26]

Memory does not add up, so it looks fine.

 

[chuckshissle]

Well, they advertise it as 1Gb of memory, that's because it's 2 x 512Mb (SLi). That's normal for gpus.

 

[khundkar]

Well, they advertise it as 1Gb of memory, that's because it's 2 x 512Mb (SLi). That's normal for gpus.

I know it adds up to 1 gig of video memory. My question is, swindows supposed to see it as 1 gig video memory? or just 512 even in sli mode?

Same for 3dmark.

What happens when you have quad sli? Will it show 1 gig memory, or 2 gig due to 2 one gig cards?

 

[GrimReaperGuy]

With Quad SLi, windows should identify it as whatever the memory capacity of a single card is. Your SLi setup is reading correctly.

 

[dagonoth]

It only shows 512mb because it also has the SLI enabled. That means that you have two of the same card in there or double what its showing. Its just an annoying quirk with windows.

 

[niz]

I read somewhere that in SLI mode, the memory of both GPUs contains the same data, so perhaps to achieve that efficiently nvidia map both cards memory into the same address range, so that a single DMA write would copy the data into both cards memory concurrently.

In this case the memory of both GPUs would appear to the CPU as a single block of 512Mb.