Compared to the triple-level cell (TLC) or the quad-level cell (QLC) NAND, which is what most SSDs currently use, the hept-level cell (HLC) could bring even higher capacity SSDs by allowing 75 percent more bits of data to be fitted into NAND cell. It pretty much all comes down to voltage states, which increase exponentially with the number of bits, so QLC NAND requires 16 voltage states, while hept-level cell HLC NAND would require 128 voltage states (2^7).

In order to create such an SSD, Kioxia uses a single-crystal silicon channel, which offers lower electrical resistance compared to polycrystalline silicon, according to PC Watch.

While it all sounds great, there are still a lot of problems and issues, as the HLC NAND is eight times as complex as QLC, and the current experimental version needs to work at -196 degrees Celsius (77K) in order to reduce data read noise, making it unsuitable for commercial usage, so we do not expect HLC NAND-based SSDs anytime soon.