SDH,
It wise to be careful with M.2 on HP worsktations before the zX40 series.
I'm using M.2 drives in a z420 and z620. The z420 uses a Samsung SM951 256GB on an M.2 to PCIe adatper (Lycon DT-120) and the z620 is an HP Z Turbo Drive, also SM951-based. The other important feature in common is that they are AHCI, which apprently still need to be the case if they are used as the boot drive. Both oF these systems have UEFI BIOS and the drives installed and were recognized and usable immediately. The Z Turbo was from an unused z230 and when I connected and started it, in a few seconds it displayed the Windows 7 screen: "Using your computer for the first time." The HP OEM Windows apparently automatically activated.
It is GPT formatted by the way which is very welcome- I wanted to gradually shift everything over from MBR to GPT as I'm partition oriented as a kind of filing system: active projects / libraries / media / archive / system recovery / etc.
However with zX00 series, looking through Passmark systems baselines for z400. z600, .z800, which total almost 1,800 systems tested, there are only two using M.2. These are z800 and both use Samsung SM951 AHCI. There are number using other PCIe drives- OCZ Revodrives though, not M.2.
A poster here did update his z620 to UEFI and uses a SM951 and with the Passmark Listings, it must be possible on the z800 at least. I have been looking for results for NVMe on zX20 systems and did find a z420 and z820 using SM951 NVMe and two Intel 750 ()400GB and 1.2TB) but still very rare.
With the Z400, z600,z7800, it seems that with updating to UEFI they can then can use M.2 AHCI, and if the Samsung 950 Pro has a special onboard legacy BIO, UEFI module, or whateve reuired, that would be a very welcome technology.
I do wish Samsung would provide clear descriptions /list / directions for compatibility and installation regarding NVMe . - Perhaps I'/ve missed it. The HP zTurbo Drive probably workied instatly as the support site documentation is very good and apparently the drive has been optimized for HP z. In the listing for the Z Turbo drives that are NVME, HP clearly states that they are for the zX40 series.
Cheers,
BambiBoomZ