PCIe lanes understanding.

Gerard Oedzes

New Member
Dec 4, 2022
Hello everyone,

I hope someone can give me some clarity about PCIe Lanes.

Situation with a Mellanox X3 10GB network card.

I have a PCIe 4.0x8 slot working on 4 lanes (CPU lanes)
The duo Mellanox card uses a 3.0x8 connection.

As far as I know 10 Gbps lets you transfer at a rate of 1.25 GB/s when you copy a file to another computer.
So 2 ports would have a maximum throughput of 2.5 GB/s.

The speed of PCIe 3.0x4 is approximately 3.9 GB/s.

My simple mind would say that the Mellanox card in my PCIe 4.0x8 working on 4 lanes could achieve its maximum potential and speed, but is this correct? If so? Why do they make those cards with X8 connections and not just with X4?

Thank you in advance for your answers.
My guess would be: Because you can use the card with a PCIe 2.0 x8 slot at full speed.
thnx. that would make sense.

But performance wise, i'm oké with duo nic networkcard in pcie x4 slot you think?


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