Why NAND Flash Density Gains Are Slowing: Layers Versus Bits per Cell

Two factors determine how much storage a solid-state drive offers: the number of layers a manufacturer can stack and the number of bits each cell can store. Adding layers mostly raises manufacturing difficulty, such as etching deep, precisely aligned holes, while packing more bits per cell becomes harder to achieve reliably as noise and drift shrink the margins between levels. Higher bit density also reduces write endurance, so high-capacity QLC and PLC drives suit read-heavy data rather than frequent writes. Denser cells also cause more write amplification, making rated endurance less reliable under mixed workloads. As both scaling levers grow more expensive, cost per terabyte has fallen more slowly than in the past, and the best drive for a given use depends on its write demands rather than headline capacity.