Multi-level cell

In electronics, a multi-level cell (MLC) is a memory cell capable of storing more than a single bit of information, compared to a single-level cell (SLC), which can store only one bit per memory cell. A memory cell typically consists of a single floating-gate MOSFET (metal–oxide–semiconductor field-effect transistor), thus multi-level cells reduce the number of MOSFETs required to store the same amount of data as single-level cells.

Triple-level cells (TLC) and quad-level cells (QLC) are versions of MLC memory, which can store three and four bits per cell respectively. The name "multi-level cell" is sometimes used specifically to refer to the "two-level cell". Overall, the memories are named as follows:

1. Single-level cell or SLC (1 bit per cell)
2. Multi-level cell or MLC (2 bits per cell), alternatively double-level cell or DLC
3. Triple-level cell or TLC (3 bits per cell) or 3-Bit MLC
4. Quad-level cell or QLC (4 bits per cell)
5. Penta-level cell or PLC (5 bits per cell) – currently in development^[1]

Notice that this nomenclature can be misleading, since an "n-level cell" in fact uses 2ⁿ levels of charge to store n bits (see below).

Typically, as the "level" count increases, performance (speed and reliability) and consumer cost decrease; however, this correlation can vary between manufacturers.

Examples of MLC memories are MLC NAND flash, MLC PCM (phase-change memory), etc. For example, in SLC NAND flash technology, each cell can exist in one of the two states, storing one bit of information per cell. Most MLC NAND flash memory has four possible states per cell, so it can store two bits of information per cell. This reduces the amount of margin separating the states and results in the possibility of more errors. Multi-level cells that are designed for low error rates are sometimes called enterprise MLC (eMLC).

New technologies, such as multi-level cells and 3D Flash, and increased production volumes will continue to bring prices down.^[2]