Z620 Unable to Boot from Z-Turbo Drive

[SDH]

Thanks much for doing that prior speed testing... very valuable.  Here is an update with more detail on why the SM951 AHCI can be so much higher in throughput potential than the XP941 AHCI.  Also, the SM951 uses MLC enterprise level NAND (as does the XP941).

Anandtech.com excellent reviews of these two AHCI controller based M.2 sticks:

https://www.anandtech.com/show/8006/samsung-ssd-xp941-review-the-pcie-era-is-here

https://www.anandtech.com/show/8979/samsung-sm951-512-gb-review

Turns out the SM951 also did get a NVMe controller after all...

My recall was that PCIe gen 3.0 could provide up to twice the bandwidth across the PCIe bus versus PCIe gen 2.0, but it is more complicated than that, having also to do with how many electrical "lanes" can be used by the PCIe device.  See the Wiki chart below that gives some perspective on how much better the thoughput is for a device that can run on PCIe 3.0 and 4 lanes (3.94 GB/s) vs PCIe 2.0 and only 2 lanes (1.0 GB/s).  You never get 100% benefit from such things in the real world, of course.

SATA III, in contrast gets you a max throughput of 6 Gbps (= same as "6 Gb/s"), which converts over to 0.75 GB/s due to the bits vs bytes thing. Thus, a ZTD G1 card running a HP SM951 AHCI stick will be quite significantly better in throughput than one running a HP XP941 AHCI in a Z Turbo Drive G1.  A ZTD G2 drive in a ZX40 is best for that workstation, but a ZTD G1 drive with a SM951 AHCI stick in a ZX40 is nothing to sneeze at.

That about covers it... the best inside info from all of us you'll find on the ZTD G1 vs G2.