NAND is the hard disk or SSD for mobiles, as it serves the iPhones for storing non-volatile data. And 3D NAND provides layers of memory cells stacked upon each other. This makes the iPhone able to store more information but in the same physical space.
According to a Digitimes report, Toshiba and SK Hynix have fallen to about 30% short of production because of poor yields of 3D NAND chips. Apple turned to Samsung for coping up with the shortfall. The 3D NAND chips have been used by Apple since with iPhone 7.
The yet immature production of 3D NAND makes it deliberate for suppliers for producing bad batches because of tight tolerance. Due to the high stake of the iPhone supercycle in 2017, it is not healthy for Apple to risk such congestions.
The 3D NAND output of Samsung is quite stable as far as yield rates are concerned. This is why Apple turned to Samsung for firing up the production of the 3D NAND chips to serve the upcoming iPhone devices. While the iPhone 7 contains 48 layers of the NAND chips, it is rumored that the iPhone 8 is going to pack 64 layers.
The to-be-launched iPhone devices of this year are to have two NAND storage sizes – 64GB and 256GB. This is matched with the latest iPad Pros with 64GB base model, though iPads currently can be maxed out to a 512GB storage configuration.
Apple does have the money to straighten supplies despite standstill in production. But other vendors are suffering for the lack of NAND flash that is happening worldwide. The issue is not likely to improve until the next year.