Solid-state drives (SSDs), which consist of NAND ash memory chips, are widely used today as a primary medium of data storage. SSDs are found within large-scale data centers, consumer PCs, and mobile devices, as the per-bit cost of NAND ash memory has greatly decreased and, as a result, SSD storage capacity has greatly increased. These improvements have been enabled by both aggressive process technology scaling and the development of multi-level cell (MLC) technology. In earlier ash memory generations, each ash cell could store only a single bit of data (a single-level cell). A multi-level cell stores two bits of data within a single cell [3, 12, 21, 25, 37, 41], thereby doubling storage capacity.

https://pdfs.semanticscholar.org/b9bc/a3c9f531002854af48de121cdcc8e0520c7f.pdf