iPhone 18 Pro Max QLC Storage Reportedly Slows Under Sustained Writes in Testing

Apple's decision to use QLC NAND flash memory for higher-capacity versions of its recently released iPhone 18 Pro series appears to involve a performance trade-off, according to testing reported by Tom's Hardware.

The device went on sale last week. QLC (quad-level cell) storage records four bits of data in each memory cell, whereas the TLC (triple-level cell) type holds three. That higher density lets manufacturers fit more capacity into the same physical footprint, but it can reduce speed when moving large volumes of data.

The Bilibili channel Homolab tested a 1TB iPhone 18 Pro Max, which uses QLC memory, against a 512GB iPhone 18 Pro built on TLC. Both models delivered broadly similar results in 4K read tests. In a low-queue-depth mixed workload, however, the QLC unit scored 8,168 against 11,285 for the TLC model, a gap of 38%. Under heavier workloads the difference shrank, though the TLC-based phone still held a 12% lead, according to the testing.