Apple’s latest iPhone 18 Pro series went on sale last week, and the company’s decision to use QLC-based NAND for higher-capacity storage variants appears to come with a trade-off. Bilibili channel Homolab recently tested a 1TB iPhone 18 Pro Max and found that its storage performance can drop significantly under sustained heavy workloads. Since QLC stores four bits of data per memory cell when compared to three bits with TLC, it allows manufacturers to offer higher capacities using the same physical space. However, this higher storage density comes at the cost of slower performance, particularly when handling large amounts of data.