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Is there a bottleneck between a device with PCIe gen 3 x1 connection if connected to a PCIe gen2 x2 slot?
Fawkes
Posted 2019-12-16T09:37:49.830
Reputation: 15
Bottleneck - PCIe gen 3 x1 device on PCIe gen2 x2 slot
Answers
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PCIe x1 means that you have (or your card has) only one lane available. As one side of your connection is "x1" then you are limited to 1 lane.
The PCIe generation defines the maximum supported speed per lane, per the PCIe spec. A PCIe Gen 2 motherboard cannot work at Gen 3 speeds because it lacks the necessary (newer) hardware to do so.
As a result your card will be limited to PCIe Gen 2 x1 as it only has one lane available.
This means you are limited to 500 MB/s (PCIe V2 x1) instead of 985 MB/s (PCIe V3 x1).
Whether that is an actual bottleneck depends on what the card is and how much data you expect to put through it every second. For a video capture card (~50Mbit/s for FullHD h.264) or sound card (1-2MB/s), even a gigabit network card (1Gbps or 125MB/s), this speed is fine.
Mokubai
Posted 2019-12-16T09:37:49.830
Reputation: 64 434
The question is about PCIe gen2 x2, is it naive to say that I am limited to 2x500 MB/s? – Fawkes – 2019-12-16T10:01:58.350
1You said your device is PCIe 3 x1 so you are limited by that too. You are limited to the lowest gen and number of lanes which means you are limited to Gen 2 x1. The "x1" denotes physical wiring of lanes to the port/card and you cannot just use more lanes because of slower speeds, the connections are physically not present on one side. – Mokubai – 2019-12-16T10:05:38.457