So I have a Sapphire ATI Radeon HD 4650, and an EVGA Nvidia 9400 GT. My ATI has crossfire x support and I'm fairly sure my 9400 GT is SLi-tech. Is it possible to run both of these cards on one monitor?
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You cant do that, SLI only works with identical cards and crossfire only works with similar ATI cards, you cannot have an ATI card and an nVidia card working together on a single monitor.
No you can't do that. SLI and Crossfire do not mix.
The only thing you can do with both ATI and Nvidia cards is use them for multiple monitors, and even then it would just be a hassle and they wouldn't work together.
You could also run the ATI as primary display and the Nvidia card as a PhysX card for the few games that use hardware accelerated PhysX, but you need "hacked" drivers for that (google GenL 1.04ff).