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NAND flashThe type of flash memory used in a solid state drive (SSD), USB drive and memory card. For the difference between NAND and NOR flash, see flash memory.
2D NAND - Limitations
Traditional flash memory has a single layer of cells, known as "2D planar NAND." As manufacturers shrank the cells and cell walls to increase storage density, fewer electrons resided in each cell, and leakage would occur. In addition, storing two and three bits in a single cell made ever smaller cells increasingly problematic.
3D NAND - The Solution
Instead of making cells smaller, the solution was to stack layers of cells on top of one another for greater storage on a single chip. In 2013, Samsung began making 48-layer 3D Vertical NAND (V-NAND) chips, eventually offering 64 layers. Other manufacturers followed with their own 3D NAND products. In 2017, SK Hynix announced a 72-layer 256GB NAND flash chip using trilevel cells (see MLC).
Why NAND and NOR Monikers?
NAND and NOR are logic gates, and their names were chosen for flash memory due to the way the two different flash circuits are wired. See logic gate and flash memory.