A report from the Taipei Times mentions that flash memory maker Macronix is moving on its 3D NAND in the second half of 2020, and apparently their first customer is Nintendo. Macronix is the company behind the flash memory in the current Switch game cards, so it wouldn't be surprising to see them handling the 64 GB option as well.
QUELLE und TEXT: https://gonintendo.com/stories/351781-switch-64-gb-game-cards-look-set-for-2020-release

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