• Card uses PCIe 3.0 x1 interface
• Existing form-factor
• PCIe interface, NVMe protocol.
• Support of legacy SD interface for backward compatibility (since the existing SD/PCIe card uses UHS-II/III pins, it is logical to expect the upcoming standard to support appropriate signaling too).

Western Digital demonstrated an experimental SD card featuring a PCIe Gen 3 x1 interface at Mobile World Congress. Meanwhile, the SD Card Association is calling upon the industry to adopt PCIe as a standard interface and to support the development of a complete SD PCIe standard.

Western Digital is demonstrating a system featuring an M.2-to-SD adapter with an SD card that offers 880 MB/s sequential read speeds as well as up to 430 MB/s sequential write speeds, according to the CrystalDiskMark benchmark. The drive uses the existing UHS-II/III pins to construct a PCIe 3.0 x1 interface with the system (via a mechanical adapter) and probably standard PCIe voltage with a converter. The company is not disclosing the type of memory or the controller that power the SD PCIe card, but it is clear that we are dealing with a custom solution. Meanwhile, Western Digital claims that the implementation costs of a PCIe interface is not high as one might expect, as a PCIe x1 PHY is not all that large.

https://www.anandtech.com/show/12487/western-digital-displays-sd-card-with-pcie-interface