Multi-Level Cell NAND

Check the number before interpreting the acronym. Samsung's 870 EVO datasheet calls its NAND 3bit MLC, while the 870 QVO specification uses 4bit MLC. These are TLC and QLC respectively, not two-bit parts. The convention used here separates the three entries without treating the broader terminology as an error.

The states are distributions of threshold voltage, not four exact voltages shared by every cell. KIOXIA describes sensing relative to read-reference voltages. More encoded states within a comparable voltage window tighten the sensing problem; that observation is not a measured failure-rate comparison between finished drives.

Keep architectural questions separate. Planar versus 3D describes cell arrangement, while two-bit MLC describes encoding. A product can combine vertical stacking with multi-bit cells. Neither choice determines whether the host talks SATA or NVMe.

To compare endurance, start with the exact drive capacity, rated workload and warranty conditions. KIOXIA's endurance brief distinguishes NAND cycling from host writes and explains why write amplification, spare capacity and error correction matter. A P/E specification for one component is not a warranty for every SSD using that encoding.

Field evidence complicates a simple SLC-over-MLC reliability ranking. Schroeder, Lagisetty and Merchant studied custom Google drives across six years and found no SLC advantage for uncorrectable errors, repairs and replacements within typical lifetimes. Models within each generation shared firmware and ECC. That makes the comparison informative, but it is not a randomized trial or evidence about today's TLC and QLC SSDs. Lower raw bit error rates did not reliably predict fewer uncorrectable errors in that population.