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NOR memory chips and NAND memory chips

We generally distinguish between two types of flash memory chips: NOR memory chips, in which several memory cells are connected in parallel, and NAND memory chips, in which several memory cells are connected in series.

But what exactly sets the two apart from each other?

  • NOR memory chips are up to four times faster than NAND memory chips and have the same storage capacity, but take up more space due to their design. The individual memory cells are differentiated into MLC and SLC cells.
  • NAND memory chips are cheaper to produce, and NAND MLC flash memory chips are the most widely used. The wear-levelling process distributes SD card controller access across various memory cells. This alone significantly increases the life of the individual memory cells. In addition, the SD card controller provides special mechanisms to supply defective memory cells with spare cells. This results in highly reliable and durable SD cards.

Flash memory cell physics

The flash memory technology is based on CMOS technology utilizing the metal insulator semiconductor field effect transistor (MISFET).

These special transistors are loaded by applying high positive voltage or erased by applying significant negative voltage.

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06.12.2014

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