Gpu - sli

[8721markc]

i have just built a nex computer it has 1 x gpu gtx 560 1280 mb i am looking at putting a second gpu in, what gpus are compatible with each other in SLI-do they need to be identical, would 2 gpu at say 1 gb ddr5 = the same as 1 gpu at 2gb?

 

[speedx77x]

When doing SLI, the cards have to be the same chip. For example, you can do SLI with 2 560's, 2 780's, 3 770's, 4 Titans,etc.

When doing SLI with different amounts of VRAM, the card with the higher amount will only use the amount of the lower card. For example, when you have a 560 with 2Gigs of Vram and another 560 with 1Gig of Vram, the first card will only use 1Gig of Vram to match up with the second card.

 

[8721markc]

so 2 x gtx 560 @ 1248mb in sli will match and give 2.5gb?

 

[Jiniix]

In theory yes, but they share the memory. So you basically have 1.25GB RAM on both cards, but all memory related items has to be run through both cards - so you only end up with 1.25GB usable RAM.
Also make sure your motherboard can run 8x in both PCIe slots. Only Crossfire can run in a 4x slot, SLI requires all cards to be in a 8x.

 

[SpringWater]

so 2 x gtx 560 @ 1248mb in sli will match and give 2.5gb?

No, you will get 1248mb shared between the two cards. Vram doesn't add up in sli, it's just whatever the card with less vram has.