The M.2 slot is not capable of 4 lane speed because anybody purchasing this fully expects it to be. Having a fully functional M.2 slot that handled the latest SSD's at FULL SPEED is a BIG reason I bought this. Needing an adapter is unacceptable.
I don't think I am telling you anything you don't know. Dell only sold it with SATA3 SSD. You can buy an adapter card and plug it into the 4x PCIe slot giving you the full speed of a PCIe SSD.
The 2015 XPS 8900 specifications PDF nor the Service Manual PDF mention the actual speed of the M.2 NGFF (Next Generation Form Factor) slot for M.2 2280 SSD. Slot 1 reserved for the WLAN. Slot 2 reserved for the SSD.
The XPS 8900 Service Manual PDF page 16 shows us two M.2 slots =
#26 = M.2_SLOT1 for Wi-Fi and Bluetooth combo card above the blue PCIe x16 video card slot
#16 = SSD SATA3 M.2 slot right of SATA ports. Keyed for M+B SATA SSD
Addonics is very pricey there are cheaper alternatives.
The Samsung 850 (B keyed) is SATA3 Not PCIe so its going to be slow.
1 x M.2 x4 Socket 3 with vertical M Key design, type 2242 storage devices support(Support PCIE SSD only) the 8900 also has daughter board that the M2 42mm sits in.
They both look like M key only. The mounting on the daughterboard looks to be 42mm. This is how a pci-e X4 card is setup below.
Diagnostics & Tools
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