There are two types of Flash memory most commonly acknowledged: NAND and NOR Flash. NOR Flash was the first of the two to be introduced in 1988 by Intel, while NAND Flash was later introduced by Toshiba in 1989. Their main differences can be identified in their architecture.
NOR and NAND is named for the way the floating gates of the memory cells that hold data are interconnected in configurations that resemble a NOR or a NAND logic gate.
NOR Flash is optimized for random access capabilities where it is able to access data in any order and doesn’t require following a sequence of storage locations. In terms of its architecture, each of the NOR flasher arm programmer cells is connected in parallel where one end of the memory cell is connected to the source line and the other end is connected to the bit line. This allows the system to access individual memory cells.
Conversely, NAND Flash is optimized for high-density data storage and gives up the ability for random access capabilities. NAND Flash cells are connected, usually eight memory transistors at the time, in a series to the bit line called a string. Here, the source of one cell is connected to the drain of the next one. This series connection reduces the number of ground wires and bit lines.
In summary, NAND-based Flash memory is ideal for high-capacity data storage, while NOR-based Flash memory is best suited for code storage and execution, generally in small capacities.