How NAND Flash Memory Stores Data

Storage devices such as memory cards, USB flash drives, and SSDs use NAND flash memory to store data. NAND flash is categorized as SLC, MLC, or TLC depending on the method of data storage.

SLC (Single Level Cell) = 1 bit, MLC (Multi Level Cell) = 2 bit, TLC (Triple Level Cell) = 3 bit

The smallest unit of digital data is called ‘bit’. A single level cell (SLC) stores 1 bit of data as either 0 or 1 in a single cell. A multi level cell (MLC) stores 2 bits of data, as 00, 01, 10, or 11. A triple level cell (TLC) stores 3 bits of data per cell, with 8 possible states. While each cell occupies the same physical space if the process is the same, the data storage capacity of the cell and possible applications vary depending on the data storage method. For example, to create a product with a 64-bit capacity, 64 SLCs (which store 1 bit per cell) are required. For the same product, 32 MLCs or 22 TLCs would be needed. SLCs have simpler data storage and retrieval compared to MLCs or TLCs, so they’re generally faster and have less errors. For this reason, SLCs are used in storage devices for automobiles or aircraft that require high reliability for an extended period. Compared to SLCs, MLCs or TLCs have more technical complexity in implementing high speed. However, an advantage is that a product of the same capacity can be made with less space. This means that the actual number of chips with the same capacity that can be fabricated on each wafer (net die) increases, making MLCs and TLCs more cost competitive. SLCs, MLCs, and TLCs are used in a range of applications, from next-generation data centers and enterprise servers to PCs. Speed, service life expectancy, and warranty is determined depending on the cell type used.