The X299 Micro has three full-length PCIe slots, supporting up to 2-way graphics. The physical slot configuration allows for a dual slot GPU to fit in the primary GPU slot (top) and the secondary just below it. Technically EVGA’s manual suggests support for SLI plus an additional PhysX graphics card, should single-slot GPUs be in play, with the third slot being a PCIe 3.0 x4 from the chipset.
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