The reference to x1 for #24 (pages 16/17) in the online XPS 8900 Service Manual was never corrected. The online XPS 8900 Specifications PDF "Ports and connectors" shows PCIe X16/x4/x16. Which matches the correct notation on the internal XPS 8900 training page.   [IMAGE] [IMAGE]
Forever I've had a card that holds an M.2 NVME SSD installed in the only short slot there is.  The service manual labels it as X1 slot.  It was a left over 256Gb M.2 NVME that came with some system.  I'm not sure why I thought it would work years ago but I plopped it in and it's worked fine.  I can't remember where I got the adapter card.  It's just one of those M.2 NVME PCI-e cards that holds a single M.2 Before replacing it with a larger one I decided to benchmark it to determine if I should just get an M.2 SATA to replace it.  I have a different adapter card to hold a pair of M.2 SATA's in an X1 slot.  So I benchmarked it and was surprised that it greatly exceeded M.2 SATA SSD speeds on the MB SSD but was still not surprisingly below the NVME in the actual X4 slot.  Hmmm, might as well just get another NVME then.   So today I replaced that 256Gb with the one below.  Now I'm stunned.  The X1 slot out performs the X4 slot.  Though the X4 slot does have an older 960 EVO.   I've not tried real world copies yet nor CrystalDiskMark.  The Samsung utility identifies the slot holding the 970 as PCI-e Gen 3 X4.  But then I would not be surprised that the adapter card itself is "telling" the Samsung utility that's what it's "looking" at.   I guess the real test would be to copy from the 960 to the 970 and watch for smoke.     [IMAGE]  
XPS 8900, is the x1 slot really an x4 slot?