NAND flash memory

NAND flash memory is nonvolatile storage built from cells connected in series strings. It reads and programs data in pages but erases it in larger blocks, enabling dense, persistent storage.

NAND flash cell: A transistor-based storage element that retains data as an electrical charge or threshold-voltage state. Its stored charge encodes each bit, or multiple bits, in a NAND array.
Floating-gate MOSFET: A transistor with an electrically isolated gate that can retain charge and shift its switching threshold. Many NAND cells store information by changing this transistor’s threshold voltage.
Solid-state drive: A data-storage device that uses solid-state memory rather than rotating magnetic disks. SSDs use NAND arrays for persistent storage and controllers to manage them.
NOR flash: A flash-memory architecture that provides direct random access to individual memory locations. NOR supports finer-grained reads and execution in place, unlike NAND’s page-oriented design.
Multi-level cell: A flash-memory cell that stores more than one bit by representing multiple threshold-voltage states. Packing multiple bits into each NAND cell raises density but narrows read margins.
NAND flash page: A unit of NAND flash memory that is read or programmed as a group of cells. Page-level access determines how data is read and written.
Threshold voltage: The gate voltage at which a transistor begins to conduct appreciably. NAND controllers distinguish cell states by measuring threshold-voltage ranges.
USB flash drive: A portable storage device that combines flash memory with a USB interface. NAND enables compact removable storage without moving parts.
DRAM: Volatile semiconductor memory that stores each bit as charge in a capacitor and requires periodic refreshing. DRAM is much faster for working memory but loses data when power is removed.
3D NAND: NAND flash built from vertically stacked layers of memory cells. Vertical stacking increased capacity as planar cell scaling became difficult.

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