I have a NVIDIA GeForce 8600FTS 256MB. I am wondering if I buy other video card NVIDIA GeForce 880GTX 768MB will work on 2 of those on my PC or I have to buy the same type video card?
no, you don't have to have SLI. if you want the 2 cards to work in conjunction with eachother then yes, but if you just want to plug 2 cards in then you just need a board with 2 pcie slots