Looking at the hardware recommendations on the Aximmetry website. Specially the recommendations call for 2 x PCIe 3.0 x16 slots.
Does this mean that each slot needs to be wired for x16 lanes? Or does this refer to the slot size of x16?
thank you
PCI lane requirements
Comments
cp2carello@gmail.com
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I'd like to revist this conversation. Looking at the hardware recommendation on your website, the Ryzen appears to be the recommendation. This CPU has 24 lanes. If the PC only has a GPU and one m.2 hard drive (possibly two additional M.2's depending on the motherboard), it is possible to get to full PCIe bandwidth and the GPU still gets 16 lanes.
However, the moment I add in a SDI card (i.e., Blackmagic 8k Pro) the GPU will drop down to 8 lanes. It gets worse the more devices added to the PCIe bus.
For use-cases where I'm running two 4k 10bit 4:2:2 SDI streams (one ingress, one egress) @ 24fps. I did some math and it appears that it is possible to run these streams on a Ryzen, but I think that's the upper limit and I risk possible throttling or reduced frame rate depending on how the system is performing. If I need to add a 3rd stream, I think I'm in trouble.
My use-case is film production. With two 4k ingress/egress streams mentioned above, I should be ok? If adding a 3rd 4k stream - is this the tipping point to use a Threadripper? The documentation indicates Ryzen is preferred but I realize you can't cover all use-cases.
thanks
Eifert@Aximmetry
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Hi,
I should have used a different term rather than "bandwidth." The CPU platform provides a fixed number of PCIe lanes, and the motherboard determines how those lanes are allocated and routed. Many boards configure the two full-length PCIe slots as either x16/0 or x8/x8 directly from the CPU, while others may route the second slot as x4 via the chipset.The main concern is lane allocation. If installing a capture card causes your GPU to operate at x8 instead of x16, you may notice a small decrease in performance. The actual impact will depend on your GPU and whether your system is using PCIe Gen 3, Gen 4, or Gen 5.
For the capture card, ensure it is in a CPU‑attached slot that provides at least x8 lanes. Avoid installing it in a chipset-fed x4 slot, even if the slot is physically x16. For example, cards like the DeckLink 8K Pro require an x8 electrical connection. With that configuration, handling three or even four 4K 10-bit 4:2:2 SDI streams should be within the card’s specifications.
Warmest regards,
Hi,
2x PCIe 4.0 x 16 slots and it refers to the slot size (Though the GPU may require all x16 slot lanes. In other words, both slots are recommended to have x16 size, and one is recommended to have x16 lanes as well).
In general, you should check the physical size requirements for your GPU and capture card. These are usually described as PCIe x16 card slots. Next, ensure that the motherboard’s layout allows both cards to fit without obstruction.
Additionally, confirm your GPU, capture card, and any NVMe SSDs' PCIe requirements to avoid bandwidth limitations. Note that even if a motherboard has two x16-sized slots, it may not provide a full 16 lanes to both slots simultaneously. Some motherboards only support a total of 20 PCIe lanes at full speed, and newer high-end GPUs typically require a full 16 dedicated lanes for maximum performance.
Warmest regards,