SD memory cards have occasionally been used as a replacement for embedded memory since they offer easier maintenance and serviceability in the field. Typically, these cards serve as memory expansion to complement a relatively small embedded memory.
The Part 1 of the Physical Layer Specification V9.0 (SD9.0) introduces new optional features for SD memory cards enabling it to better serve as semi-embedded memory or applications in which the card needs to be tightly bound to specific host:

Boot – Fast Boot and Secure Boot features give cards the ability to serve as a device’s boot code memory by using a simple and easy fast boot code uploading process, along with secured methods of providing boot code updates

RPMB – Replay Protected Memory Block offers a secured hidden memory accessible only through a secured authentication process and provides replay protection security mechanism: especially for a secured write-protect mechanism and secured boot code update

TCG Storage – A secured storage method defined by the Trusted Computing Group adding a self-encrypted drive capability

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