This may have been discussed to death already, so my apologies if I'm covering old ground.
I decided to treat my trusty old Mac Pro 3.1 running El Capitan to an internal SSD. Impatience, lack of research and possibly a tiny bit of stupidity led me to buy a 256GB Samsung NVMe PM961. (I now know I should have bought an AHCI card, but they don't seem to be for sale any more...) I also bought a generic M.2 PCIe adapter.
Fitted it, and... no surprises, it didn't work.
A bit more Googling led...
NVMe on MacPro 3.1 Success! (sort of...)
I decided to treat my trusty old Mac Pro 3.1 running El Capitan to an internal SSD. Impatience, lack of research and possibly a tiny bit of stupidity led me to buy a 256GB Samsung NVMe PM961. (I now know I should have bought an AHCI card, but they don't seem to be for sale any more...) I also bought a generic M.2 PCIe adapter.
Fitted it, and... no surprises, it didn't work.
A bit more Googling led...
NVMe on MacPro 3.1 Success! (sort of...)