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 me to http://www.macvidcards.com/nvme-driver.html by JimJ740. As per the FAQ, installed the kext to /Library/Extensions (along with setting the permissions...) Again, nothing. Loaded the kext manually. SUCCESS! The drive appeared and was dealt with by Disk Utility. Flushed with success, I copied the kext to /System/Library/Extensions After a reboot... Kernel Panic. So, card out, reboot, delete the kext from /System/Library/Extensions. Power down, card re-installed, machine booted fine, but no sign of the drive until I manually loaded the kext again. Reboot again... Kernel Panic. Remove card. Boot fine. Shutdown. Install card. No sign of it until manually loading the kext. Lesson learned: manually *UNload* the kext before shutting down. So, there we have it. I have a working 256GB NVMe SSD, albeit I have to load and unload the kext for it, which isn't a major problem. I then wondered why it was so slow (yes, it is plugged into Slot 2, the spare PCIe 2 slot). More Googling led me to this fine forum, and after removing 16GB of ram to bring my total down to 48GB I now have quite impressive performance! (I'll add a speed-test screenshot later - on a different computer atm). So, thanks to JimJ740 and others of this fine forum. 2 problems solved for the price of one Cheers Paul B.