I created a thread with the same subject except for - no info. That thread is now locked. Creating a new thread because much of the info in that thread is incorrect or unrelated to the subject.
The Z440 does support bifurcation on the X16 slots, it can be turned on/off in the BIOS. The default is on.
PCIe slot 3, X4, doesn't work for anything on my machine; perhaps defective. When I plugged a OWC PCIe to SATA SSD adapter into the slot, with a Samsung 840 EVO 1TB on the card, the machine will not even boot. Moving the card to slot 5, a X16 slot, and everything is fine. Tried a USB3 card in the slot, again machine is dead. Moved that card to slot 1 and everything is grand. Had a similar problem with my previous Z420.
This is really disappointing as I was hoping to plug the OWC card in slot 3 and later put a dual to quad NVMe adapter card in slot 5.
From hunting around the web, it appears that HP does strange things with their PCIe slots. Guess my next machine will be a home built with an ASUS XEON motherboard that supports their VROC card. With Samsung NVMe Pro cards, it can hit over 30GB per second. That's right, gigabytes, not bits. It is just so much more expensive to build that to start with a HP workstation and upgrade it to meet my requirements (desires?).
Anyway, anyone with an idea of how to use the X4 Slot 3?