سؤال مشهورQ: Is it possible to use different videocards to get SLI?
A: You must use same GPU-s to get SLI. For example 8800GTS + 8600GTS or GTX 260 + GTX 280 will not work together, only as separate cards. If you have videocards with different memory size onboard, you still can use non-recommended SLI mode, by creating DWORD key named CoolBits with 1F value in registry HKLM\SOFTWARE\NVIDIA Corporation\Global\NVTweak. This will render "extra" videomemory unused. For example 8800GTS 640MB + 8800GTS 320MB will be the same as two 8800GTS 320MB cards. Having equal chip/memory clocks isn't necessary. But we recommend to install faster card to primary PCI-E slot, due to higher load to master card overall performance should be better