MLC NAND (multi-level cell NAND) is a form of flash memory used in SSDs, USB drives, and memory cards. Each cell stores two bits of data, compared to one bit in SLC (single-level cell) NAND. This allows manufacturers to pack more storage into the same physical space at a lower cost.
How it works: MLC cells use multiple voltage levels to represent different binary values. By reading these voltage states, the controller can determine whether each cell holds a 0, 1, 2, or 3 (in binary terms, 00, 01, 10, or 11). This density benefit comes with trade-offs.
Trade-offs:
- Speed: MLC is slower than SLC because reading multiple states takes longer.
- Durability: Each cell can tolerate fewer write cycles (typically 3,000 to 10,000 compared to 100,000+ for SLC) before degradation.
- Reliability: Voltage margins are tighter, making MLC more sensitive to electrical noise.
Real-world example: A budget SSD rated for 200GB capacity often uses MLC NAND. A premium SSD of the same size might use TLC (three bits per cell) or QLC (four bits per cell) instead, which are even denser but slower.
When shopping for storage, understand that MLC is now largely phased out in consumer products, replaced by faster TLC and more affordable QLC options. If you see MLC listed, you're usually looking at older stock or specialist hardware. For typical use (documents, photos, games), the speed difference won't be noticeable, but MLC drives wear out faster under heavy workloads like video editing or continuous file transfers.