NAND flash

NAND flash is a non-volatile storage technology that retains data without power, commonly used in SSDs, USB drives, and memory cards. It stores data by trapping electrical charges in a grid of memory cells, where the data remains even after the power is removed. Its design allows for high-density storage in a small form factor, making it ideal for mass storage devices. 

Key characteristics

• Non-volatile: Data is not lost when power is turned off.

• High-density storage: Memory cells are stacked vertically, allowing for a large amount of data to be stored in a small space.

• Serial access: It uses a serial access method, making it faster for writing and erasing large blocks of data but slower for reading individual bytes compared to NOR flash.

• Cost-effective: It is a cost-effective solution for mass storage, making it popular for consumer electronics. 

Common applications

• Solid-state drives (SSDs)

• USB flash drives

• Memory cards (like SD cards)

• Smartphones and tablets

• Digital cameras

• Gaming consoles 

Types of NAND flash

• Single-Level Cell (SLC): Stores one bit per cell; offers the highest performance and endurance.

• Multi-Level Cell (MLC): Stores two bits per cell; balances cost and performance.

• Triple-Level Cell (TLC): Stores three bits per cell; offers high density at a lower cost, but with slower speeds and lower endurance than SLC or MLC.

• Quad-Level Cell (QLC): Stores four bits per cell; provides the highest density but is the slowest and has the lowest endurance. 

How it works

• Storing data: Data is stored as electrical charges in memory cells, which are a type of transistor.

• Writing data: An electrical charge is applied to trap electrons in the cell, which changes the threshold voltage.

• Reading data: A small voltage is applied to check if the channel turns on. If it does, it indicates a binary "1" (no charge); if it doesn't, it indicates a binary "0" (charge present).

• Erasing data: Data must be erased in entire blocks, not individual cells. This process sets all bits in the block back to "1".

• Wear and tear: Each erase/write cycle (P/E cycle) wears out the cell, so flash memory has a limited lifespan. Technologies like wear-leveling are used to distribute write cycles as evenly as possible across all cells to extend the life of the device.