To anyone who wants to boot windows from pcie x1, I did some research last night and turned out it was very easy. Using : 1x nvme m.2- original m.2 card came with the xps 8940, windows installed 1x nvme m.2 to pcie x1 adapter (Sintech M.2(NGFF) M Key SSD to PCIe X1 Adapter) Steps: 1) insert the m.2 into the pcie adapter and install it into the pcie x1 2) restart pc and press F12 and change the BIOS settings 3) disable security boost 4) change to AHCI mode, apply 5) Exit and reboot, it may take a little while to get into windows(15 seconds for me). Once you see the windows screen, restart pc.  6) Press F12, go back to BIOS settings and enable security boost ( boot up time will be shorter). 7) Done. I did it less than 15 mins including change parts and setting etc. Maybe it was not possible in the past, but guess Dell's new motherboard somehow upgraded ? I'm not sure, but I'm happy that I can free up the m.2 slot for other purpose. Note: pcie x1 is way slower than the m.2 slot on xps 8940, here are the readings from the same nvme m.2 card: ================== m.2 slot: Read: 3267.64 MB/s Write: 3047.84 MB/s ================== pcie x1: Read: 878.59 MB/s Write: 836.47 MB/s ================= I only use the system to read documents and watch some films, so the pcie x1 speed is good enough for me. Hope this help guys.      
Hi all, For some reasons I need to boot a nvme M.2 (original C: with windows installed) from pcie x1. I bought a nvme M.2 to pcie x1 adapter and inserted in the slot and the xps 8940 couldn't recognize it (boots windows from it). I've changed to an empty M.2 card into the pcie x1 and using it as my 2nd drive at the moment. However, I really need to use the pcie x1 to boot windows 10. Thanks in advance!      
XPS 8940 Boots Windows from pcie x1