ConnectX-3 pro En in x4 slot

Hessam2013

New Member
Dec 20, 2016
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HI,
Back again

Was comparing CX3 with CX3 pro cards and found out that CX3 cards will work in x4 mode when connected to pcie3 (x8 in gen2), but nothing about this in XC3-Pro En but these lines:
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A lesser width adapter can be seated into a greater width slot (x4 in a x8), but a greater width adapter cannot be seated into a lesser width slot (x8 in a x4). Align the adapter connector edge with the PCI Express connector slot.
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Now, I am confused, as the card has the auto_negotiation capability with x1, x2, x4 as datasheet says and pcie3 x4 is enough bandwidth for dual 10gb sfp+, what happens if u use one of this cards in x4 slot(Provided that the slots end is open and card physically can seat on mobo's slot)?
Any performance issue?
every hint will be appreciated.

Regards,
Hessam