This is where the specification’s most demanding updates reside.
The M.2 specification continues to provide a family of form factors designed to replace older Mini Card and Half-Mini Card solutions with a more compact and scalable design. pci express m.2 specification revision 5.0 version 1.0 pdf
The only practical issue arises if a Rev 5.0 host expects SRIS and attempts link training with a Rev 4.0 device that only supports Common Clock. The specification requires hosts to retry training with fallback architectures before declaring failure – a process called , newly defined in Rev 5.0 Annex L. This is where the specification’s most demanding updates
: The specification introduces improved amperage support for M.2 connectors, accommodating the increased power needs of high-speed controllers and high-density NAND flash. pci express m.2 specification revision 5.0 version 1.0 pdf