Lennart Sorensen wrote:
> Well certainly so far it looks like early onboard designs
> are going to be a compatibility mess.
For ATX/ITX mainboards ...
Anyone with an office in Taiwan or China can be a mainboard OEM
overnight. ECS, FIC, FoxConn and a handful of other ODMs will cater
to you, and let you add all sorts of stupid things, and not bothering
to QA check anything that isn't in their core peripheral set. There's
always room on the board to add something.
This will include how you trace out your M.2 slots, including outside
of spec. Asus has officially hit rock bottom as an OEM if you ask me.
For notebooks mainboards ...
You better know what you're doing as an OEM, because you're heavily
limited by packaging, thermals, etc.... And that usually just going
to Clevo as your ODM, and changing _nothing_.
> No they really do seem to be doing NVMe
> by using the PCIe link of the M.2 slot.
Huh? NVMe ~ AHCI != PCIe ~ SATA
"As a logical device interface, NVM Express ..." [1]
^^^^^^^ Logical (not physical)
More specifically (the SSD "hardware") ...
"NVM Express SSDs exist both in form of standard-sized
PCI Express expansion cards ..." [1]
(as I said)
And ...
"as 2.5-inch drives that provide a four-lane PCI Express
interface through the U.2 connector (formerly known as
SFF-8639)." [1]
And more specifically ...
"SATA Express interface supports both PCI Express and
SATA storage devices" [2]
And ... (only a new development in early 2015, but looking to be the
standard "SATA Express" going forward.
"The U.2 connector is mechanically identical to the SATA
Express device plug, but provides four PCI Express lanes
through a different usage of available pins." [2]
In other words, they've made the new U.2 connector purposely to be
mechanically compatible with SATA Express, so the existing SATA
Express connector can be used.
This was not unlike mSATA, where they used the Mini-PCIe slot to run a
SATA channel. It's ironic that we've gone from hacking SATA into PCIe
connectors to PCIe into SATA connectors.
But _none_ of this has to do with AHCI.
It's just that the updated SATA Express connectors with U.2 electrical
are new enough they are going to be NVMe-only. But they have
_nothing_ to do with NVMe, which is just a logical approach.
> Yes they are aiming for the 2.5" NVMe drives, like the intel 750
> (SSDPE2MW400G4R5 for example), which is listed as a 2.5"
> drive with a PCIe 3.0 x4 interface. Sure looks like a SATA
> connector of course.
It _is_, physically, SATA Express.
SATA != SATA Express.
SATA Express is backward compatible SATA compatible.
SATA Express PCIe and U.2 are mechanically compatible.
SATA Express PCIe (x2) and U.2 (PCIe x4) are not electrically compatible.
And SATA Express adoption is seemingly only going to happen with the
U.2 connector, which is well-timed for NVMe.
> Of course given the same size intel 750 can be bought for about the
> same price as a PCIe 3.0 x4 card to plug into a slot instead, for a
> desktop or server that may well be the better way to go and avoid
> adapters and weird cables and such.
I would only buy a M.2 or SATA Express device so I can use it anywhere.
But that's just me.
-- bjs
--
Bryan J Smith - http://www.linkedin.com/in/bjsmith
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