On: The death of the PCIe expansion card

[c_o_n_v_e_x]

PCIe bifurcation is a function of what your CPU and/or PCH can do. There are hard limits in the silicon as to how you can divvy up your lanes.

[fomine3 → c_o_n_v_e_x]

Splitting CPU lane to x8/x8 is supported at least. Just mobo manufacturers don't want to implement it as a dedicated slot. It seems that Alder Lake no longer support x8/x4/x4 sadly.

[wtallis → fomine3]

> It seems that Alder Lake no longer support x8/x4/x4 sadly.

I would be very surprised if the silicon doesn't still support 8+4+4 operation. I suspect the lack of available motherboards with this config comes down to the expense of getting a PCIe gen5 signal to reach the third slot. It may require both the extra mux and a redriver or retimer.

[fomine3 → wtallis]

I found this from quick Googling https://forum-en.msi.com/index.php?threads/does-pro-z690-a-a...

Perhaps why they dropped the support is because the reason you wrote? Still I wonder is it possible to have Gen5 x8 and Gen3 x4/x4.

[eigen → fomine3]

> It seems that Alder Lake no longer support x8/x4/x4 sadly.

Sort of. support is "Up to 1x16+4, 2x8+4" [1] so could be used as x8/x4/x4, the remaining 4 lanes are unused in the x8, as there are 20 PCIe lanes on the CPU.

[1] https://ark.intel.com/content/www/us/en/ark/products/228441/...

[fomine3 → eigen]

Ah yes, but everyone (and every manufacturer) want to use +x4 port for M.2 SSD so not usable for other PCIe devices.