Sharing RAM in SLI

[iostream]

Good afternoon,

I am contemplating running two cards in SLI. If I understand things correctly, only the ram from one card will be used, however I can't find a definitive answer. ie if I have two 512MB cards in SLI will I will still only have 512MB of vram to play with, not 1GB?

Therefore would running a faulty card (eg lines down the screen) as a daughter SLI card work just fine if it was the ram that was corrupt? Anyone have any experience running a faulty card as the daughter card in SLI?

Faulty cards go nice and cheap on ebay

 

[straxusii]

All the ram will be used in both cards however they both need the same content so to all intents you can consider the vram limit compared to a single GPU as halved.

So a 2GB 5970 is effectively 1GB, 2 1GB 5870 in crossfire have effectively 1GB

 

[Boozebeard]

So to answer his question, a 512mb and a 1gb in SLI would be limited too 512mb?

 

[marc512]

So to answer his question, a 512mb and a 1gb in SLI would be limited too 512mb?

no. other way around. 1024mb on top, thats your limit, 512mb on top (1024mb as sister card) yes it would be limited to 512mb

 

[opethdisciple]

Yea, took me a while to see it, but ensentially, when twocard work in crossfire the minimum amount of ram on one card, becomes the buffer size for both.

Both card use their own vram, to buffer, so essentially two 1gb 5870's only have 1gb of vram, (thats only becuase each card has one each)

If you took two 2gb 5870's in crossfire, then the vram would be 2gb.

Crossfire 1 521mb 4870 with a 1gb 4870 and you have 512mb vram (512mb each however), it just appears as one block of 512mb...

 

[mame]

each cards' memory is a mirror of the other cards' memory so both your cards will need 512mb of working memory to have a total of 512mb memory. Basically, you have 2 of everything so it needs 1gb to have 512mb's worth of unique data.

 

[iostream]

Thanks for the responses, makes sense now. Won't chance my luck with a broken card as the daughter card as it will most likely be a waste of money..