Four basic types of NAND flash are used in an SSD based on the number of bits stored in each cell. With each type of NAND, there are cost, density, performance, and endurance characteristic trade-offs.
Single-level cell (SLC) stores only 1 bit of information and requires only 2 voltage levels to represent 0 or 1. This is the simplest implementation of NAND and has the highest cost and endurance.
Multilevel cell (MLC) requires 4 voltage levels to represent 00, 01, 10, and 11
Triple-level cell (TLC) requires 8 different levels
QLC needs 16 distinct levels. QLC NAND flash has not only the highest density and lowest cost but also lower endurance and write performance compared with other types of NAND flash.