Apple is using a 128GB NAND flash die in Apple Watch Series 12 and Ultra 4 models, claims a Chinese hardware researcher, despite both devices officially offering only 64GB of storage. It's unclear why Apple would limit the accessible capacity, but it could conceivably be reserving some of it for intensive sensor data read/writes or as a durability buffer.

Something similar happened with the M4 iPad Pro in 2024, when teardowns indicated that 8GB models actually contained 12GB of physical RAM, with only 8GB made available to the system. Intriguingly, a 128GB NAND storage profile tied to the T8320 chip for the Apple Watch Series 12 and Ultra 4 was discovered earlier this month.

Teardowns will hopefully clarify the situation. This article, "Apple Watch Series 12 and Ultra 4 May Have Hidden Flash Storage," first appeared on MacRumors.com.