Fall 2015 Solid State Drive Technology Update

Since our last SSD update article, the last 7 months have seen no shortage of exciting announcements, and the enthusiast market has rapidly evolved in both positive and confusing ways. Let’s get up to speed on U.2, NVMe, 3D XPoint, M&A, and the rest of the buzzword soup that make up this market.

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Demystifying Form Factors and Interfaces

What was confusing in March of this year has become slightly more impenetrable to casual observers. The primary factor making the current SSD market situation somewhat complicated is the variety of host interfaces, protocols, and form factors currently available. While the luxury of choice is certainly present, there are compatibility landmines at every turn.

The M.2 standard provides different physical connector keying, with each key type supporting combinations of SATA, PCIe, and a few others that aren’t relevant to this discussion. The letters A-M represent the key types in the M.2 standard, with A, B, E, and M being the ones that could potentially be used for SSDs. Let this be a note of caution on M.2; caveat emptor, and make sure that you read the fine print.

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M.2 edge connectors (credit: NikNaks, license)

Even this reviewer was recently forced to reintroduce his palm to his face when trying and failing to test a SATA M.2 SSD in the world-beating, does-it-all ASUS Rampage V Extreme motherboard in his test system. The M-keyed drive physically fit in the M-keyed socket as one would expect, but wasn’t recognized by the system. As it turns out, the M.2 socket on the Rampage V Extreme is a type that only carries PCIe and not SATA signals, while the M-keyed connector is permitted in the M.2 specification to support PCIe x4 as well as SATA, it took some quick, frustrated research to realize that "supported" does not imply "present."

With the Skylake launch, M.2 sockets have become much more commonplace on motherboards. At the beginning of the year, boards with a single M.2 sockets were still relatively rare, but now a number of manufacturers offer boards with two sockets, and ASRock is now shipping two different Z170 boards with three M.2 sockets.

When considering an SSD, remember that NVMe is only possible over the PCIe bus. Of course, not all PCIe drives will support NVMe anyway and most current drives are still on AHCI, and in fact many of those aren’t even native PCIe devices. An attempt to make sense of the interface, protocol, form factor, and connector madness is shown below.

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