UEFI class and PCI-E 3.0 Bus are the issues.  Models that came out after  2013 and have windows Genuine COA will be UEFI Class 2.3.1 complaint.  Its likely that they also have PCI-E bus 2.1 or newer. That means 9020 models and newer. The 7010 has CLASS 1 UEFI which does not allow GPT booting because its compatable with 32 bit XP with MBR. [URL] Machines like the 790 and 7010 will never have class 2.3.1 UEFI secure boot bios.  One reason is that they support 32 bit XP as well as MSDOS and MBR Legacy booting.  All new systems past skylake chipset are WIN10 only 64 bit only end of story.  No more legacy booting or OS. PCI-E bus uses 8b/10b encoding and slower bus speed for version 1 to 2.0 PCI-E bus uses 128b/130b encoding and much faster speed for 2.1 and 3.0 and up. Thats why Older models like Precision 490 and 690 with PCI-E 1.1 bus cannot use newer cards.  Fitting into the slot does not guarantee working even when there is sufficient power to go along with that aka 1000W power supply.  PCI-E is not backwards or forwards compatbile for secure boot and power and line code reasons. Intel started discussing this back in 2009 [URL] PCI-E  M key only booting became standard with UEFI Class 2.3.1 bios. [URL] It started with windows 8.0 and continues today with 8.1 and 10. Secure boot and PCI-E booting are the main features. [IMAGE]CSM is in Class 0 and 1 and 2[IMAGE]Newer Systems Do not allow LEGACY MBR Booting[IMAGE]UEFI is currently Class 2.3.1  
Hi, a couple of days ago I tried to upgrade some Optiplex 790 and 3010 SFF computers and get rid of good ol' SATA HDDs/SSDs by using a PCIe -> M.2 Key M adapter with a current M.2 Key M NVME SSD but after some hours I figured out that both systems aren't able to boot from those SSDs as their individual UEFI lack support and only a handful of older SSDs like the Samsung 950 Pro would work - with some drawbacks like using the PCIe Adapter in the first PCIe 16x slot, using MBR instead of GPT and so on. As I'm quite curious if there is some kind of support matrix regarding Optiplex' and their ability to boot from NVME M.2 Key M SSDs via UEFI I've chatted with a Dell supporter but only got a hint that current models would support it. No hint about older models (also system specs don't list such stuff) so I hope I can get this question answered via this forum post  tl;dr Which Optiplex model (the older, the better) does support booting from NVME SSDs via UEFI. Thanks D.
Optiplex Model Overview regarding UEFI PCIe NVME M.2 Boot Support