0

This is for a high bandwidth ssd. I know I can plug the pcie 4.0 card into a pcie 3.0 x16 port directly, but then I would be stuck at the bandwidth of pice 3.0 x16 which wouldn t be able to exploit the full speed of the ssd.

But since I m having pcie 3.0 x24 ports, why not take the additionnal speed offered by x24 over x16 in order to approach the bandwidth of pcie 4.0 x16?
I meaning to get the speed of pcie3.0 x24.
Since it s about using more slower lanes to approach the speed of faster lanes, is it possible?

Of course, I m also thinking about specialized dedicated adapters.

user2284570
  • 1,799
  • 7
  • 35
  • 62
  • PCIe doesn't work like that. PCI 4.0x16 can only run at PCIe 3.0x16 if plugged into a PCIx16 3.0 slot. – Ramhound Sep 09 '20 at 17:56
  • What kind of SSD is capable of saturating DDR4? – Bryan Boettcher Sep 09 '20 at 18:06
  • @BryanBoettcher https://geizhals.eu/gigabyte-aorus-gen4-aic-ssd-8tb-gp-asacne6800tttda-a2180654.html – user2284570 Sep 09 '20 at 18:18
  • @Ramhound I m talking about using a pcie 3.0 x24 lanes slot for the pice4.0 x16 lanes card. – user2284570 Sep 09 '20 at 18:21
  • @user2284570 that will not saturate a 3.0 16x bus. It's a massively impressive card, but you will actually be able to use the full bandwidth of the card. – Bryan Boettcher Sep 09 '20 at 18:40
  • @BryanBoettcher so is ipce4.0 is about things like latency in that case? Or is it a pure marketing? – user2284570 Sep 09 '20 at 18:44
  • @user2284570 - You can't use more PCIe lanes then the card is actually designed to use. What you want does not exist. Your understanding of PCIe and how backward compatibility works isn't accurate. If you plug a PCIe 4.0 SSD into a PCIe 3.0 slot, then it will be limited by the bandwidth of the PCIe 3.0, it's not possible to exceed the limits of the slot itself. – Ramhound Sep 09 '20 at 21:05

1 Answers1

3

No, PCI Express doesn't work like that. You can't split one faster PCI-e lane into two slower PCI-e lanes.

It's a bit counter-intuitive, but by combining high lane count, low version PCI-e with low lane count, high version PCI-e gives you worst of both worlds. For example a x16 v2.0 device in a x8 v3.0 motherboard will work at x8 v2.0.

What is possible with PCI-e:

  • Running higher version devices on lower version motherboards (downgrades to motherboard version).
  • Running lower version devices on higher version motherboards (downgrades to device version).
  • Running high lane count devices in low lane count slots (limits throughput to slot's lane count; if the device doesn't fit in the slot you can use a riser or carefully cut off back of the slot).
  • Running low lane count devices in high lane count slots (limits throughput to device's lane count).
  • If motherboard supports bifurcation, a single x2 or larger slot can be split into two half-slots.

Without bifurcation support, the same can be achieved by using specialized PCI-e switches. To achieve what you want you'd need a "reverse switch", but I haven't heard about such thing yet.

gronostaj
  • 55,965
  • 20
  • 120
  • 179