A flash cell stores four bits by distinguishing sixteen voltage levels. Each level matches one combination of those bits. Wider gaps separate the levels in a cell that stores fewer bits, which makes those levels easier to tell apart.
How Four Bits Fit in One Cell
A write places the cell’s charge in one of sixteen narrow windows. A read measures that charge and returns the four bits it represents. The windows sit closer together than the levels in a cell that stores one, two, or three bits.
Cost, Wear, and Read Speed
- Lower cost per bit: A cell that stores four bits costs less for each bit than a cell that stores fewer bits.
- Earlier wear: Repeated writes blur the sixteen voltage windows. The cell stops holding a reliable charge sooner than a cell that stores fewer bits.
- Slower reads: Distinguishing sixteen close levels takes longer than reading a cell whose levels sit farther apart.
Consumer and Bulk Storage
Manufacturers use the four-bit cell in high-capacity consumer drives and in bulk storage drives. The draw is more data at a lower cost per bit. The limits are earlier wear and slower reads. The table compares how many bits each layout stores.
| Cell | Bits stored |
| single-level cell | One |
| multi-level cell | Two |
| triple-level cell | Three |
| quad-level cell | Four |