Penta-level cell (PLC) flash may be the next logical step for SSDs, but Western Digital does not expect the technology to be ready until at least 2025 (via Tom's Hardware). The reason for the delay is that newer and more powerful controllers will be needed to make the transition to PLCs worthwhile.

The most common storage technology currently used in SSDs is triple-level cell (TLC) flash, which uses eight voltage levels to store three bits per cell. Quad-level cell (QLC) flash uses 16 voltage levels to store 4 bits per cell, but requires advanced error correction along with wear leveling and over-provisioning to maximize endurance. [The 32 voltage levels required for PLC flash requires even better error correction, which in turn requires a faster processor at the heart of the controller. This new flash technology also requires over-provisioning, error correction, and wear leveling to match the 25% increase in capacity.

The problem is not the flash technology itself, but rather other things in modern SSDs that can undermine the value proposition of the PLC itself, just as QLC flash memory, despite its promise, did not deliver a cheaper, higher capacity SSD. these drives require elaborate caches to mask the underlying performance of the flash technology being used.

Of course, the computing industry has a history of solving these kinds of problems, so we may see PLC SSDs by 2025. As a result, SSDs may offer hard disk drive-level capacity, but hopefully not hard disk drive-level performance. However, the switch to PLC flash is not likely to be an easy step.