Nvidia GeForce GTX745

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Yes, both are completely backwards-compatible (just like using USB3.0 in a USB2.0 or USB2.0 in a USB3.0). So, yes, you can plug in a PCIe3.0 card in a PCIe2.0 slot or a vice-versa. Of course, it will run in PCIe2.0 (at 5Gb/s instead of 8Gb/s) only. But you can't really tell a difference in performance as PCIe3.0 can't really be maxed out by such video cards at that speed.

raisonjohn

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Yes, both are completely backwards-compatible (just like using USB3.0 in a USB2.0 or USB2.0 in a USB3.0). So, yes, you can plug in a PCIe3.0 card in a PCIe2.0 slot or a vice-versa. Of course, it will run in PCIe2.0 (at 5Gb/s instead of 8Gb/s) only. But you can't really tell a difference in performance as PCIe3.0 can't really be maxed out by such video cards at that speed.
 
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