Multi-level cell flash is a type of flash memory that stores
more than 1 bit per cell. MLC flash is less expensive than
single-level flash (SLC), which makes it a popular choice for
consumer-grade solid state storage (SSS). MLC flash has a higher
bit error rate than SLC flash because there are more
opportunities for misinterpreting the cell’s state. Unlike
single-level cell flash, which only stores 1 bit per cell and is
always in one of two states, programmed (0) or erased (1), MLC
flash cells have more than two states because each bit in the
cell is either programmed or erased. MLC-2, for example, has
four states. MLC-3 has eight states and MLC-4 has sixteen; as
with SLC flash, each state is determined by the level of
electrical charge that’s applied to the cell. In general, the
more bits the cell has, the fewer write cycles it will have. For
example, a 2-bit MLC cell is good for about 3,000 to 10,000
write operations before it begins to fail, while a 3-bit MLC
cell would only have 300 to 3,000 write cycles.