ok, lets clear up some misinformation found in this thread.
1. the HP z220/420/620/820 workstations CAN NOT BOOT FROM A NVME BASED SSD, they lack the nessary bios code for this, the nvme drive can be used as a data drive however
HP has released two diffrent ssd kits for the hp workstations
the first one is the Z Turbo Drive (sometimes called the Turbo Drive G1) which is a SATA based ssd using the SM951 this kit works on the z220/420/620/820 models and should also work on previous workstation models but the HP pci-e card may not be compatable with previous workstation models (use a generic pci-e ssd carrier board)
the second drive kit is the TURBO DRIVE G2 which uses the NVME based SM951, this kit uses the same HP PCI-E card but the ssd is NVME based and is only supported on the z240/440/640/840 (and newer workstation lines)
2. the samsung sm950 and sm960 SSD NVME drives are completely diffrent items, the sm950 is a older ssd that did have the nessary nvme code embeded into it's bios which allowed it to boot on older systems that lacked native bios nvme code
the sm960 nvme drive is a newer generation SSD that no longer includes the legacy bios code, as such it is unable to boot on a system that does not have the bios support for nvme drives
3. as a general rule of which systems support booting from nvme drives you can use the intel chipset used on the motherboard as a guide x99 chipsets and newer do support booting from nvme, x79 chipsets mostly do not, but a few do, however they are quite rare, x58 chipsets and earlier will not support nvme ssd booting no matter who the motherboard maker is
SATA based SSD's will work on all motherboards as a boot drive, and the midrange/high end ssd's are not that much slower than a nvme based drive when used on a SATA 6GBps interface even a SATA 3GBps interface is not that slow for most users due to how they access files on their computer
4. pay attention to the ssd specs!!!! as a example the samsung SM951 ssd is available in both SATA and NVME and the model numbers between the two differs by only one letter!! be sure that the ssd you want to buy is the proper interface for your system (SATA or nvme)
The SM951 AHCI version carries the code MZ-HPVxxx0 (where xxx is the capacity in gigabytes),
The SM951 NVMe version is called MZ-VPVxxx0 (note the change in numbering after the " MZ- "
5. using pci-e or m.2 SSD carrier boards, these boards support one, two , four ssd's on one pci-e card
you need to pay attention to the number of pci-e links the carrier board and the SSD supports
most ssd's use either 2 or 4 pci-e links (x2/x4) and most single ssd carrier boards are x4 which allows just about any x2 ssd to work on the x4 carrier card
however the reverse is not allways true, some x4 based ssd's will not work in a x2 slot and some will. so you will have to check with the maker of the sdd to see if their x4 ssd model will work in a x2 interface
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hope the above helps people wanting to install a ssd in their computer