Apple has reportedly decided to stop using triple-level cell (TLC) NAND in some versions of its iPhone 6 and iPhone 6 Plus devices, following problems in the controller IC of the TLC NAND flash. Business Korea reports that the U.S. smartphone giant will discontinue its use of triple-level cell (TLC) NAND, since the company believes that the functional defects plaguing the 64GB iPhone 6 and the 128GB iPhone 6 Plus stem from a problem in the controller IC of the TLC NAND flash. The controller IC is reportedly made by SSD maker Anobit, which was sold to Apple in 2011.

TLC NAND flash can store three times as much data as single-level cell (SLC) that stores one bit of data, and 1.5 times as much as multi-level cell (MLC) solid-state flash memory that stores two bits of data. it's also more affordable but also slower than SLC or MLC in reading and writing data.

As a result, Apple is planning to use MLC NAND flash in the 64GB iPhone 6 and the 128GB iPhone 6 Plus in the future, according to the report. The company is also expected to release the iOS 8.1.1 update later this year that would improve the performance of existing iPhones shipped with TLC NAND.