How do SSDs utilize NAND flash memory?

SSDs utilise NAND flash memory to store data persistently, even when the power is turned off.

Solid State Drives (SSDs) use NAND-based flash memory, which is a type of non-volatile storage technology. This means that it does not require power to retain the data stored on it. When you save data, it's written to the NAND flash memory. When you need to access that data later, the SSD reads it directly from the NAND flash memory.

NAND flash memory is composed of cells, which are the smallest units that can store data. These cells are organised into pages, which are the smallest units that can be written to or read from. Pages are grouped into blocks, the smallest units that can be erased. This hierarchical structure allows SSDs to manage data efficiently.

When data is written to a SSD, it's stored in the cells within the pages. If a page is partially filled, the SSD can still write data to the remaining space. However, if a page is full, the SSD must write the data to a new page. If a block is full, the SSD must erase it before it can write new data to it. This process is known as garbage collection and can impact the performance and lifespan of the SSD.

To optimise performance, SSDs use a technique called wear levelling. This involves spreading writes evenly across the physical drive. Since each cell in a NAND flash memory has a limited lifespan, wear levelling helps to extend the overall lifespan of the SSD.

In addition, SSDs use a form of error correction code (ECC) to ensure data integrity. ECC checks the data as it's read from the NAND flash memory and corrects any errors it finds. This is crucial because NAND flash memory cells can wear out over time, which can lead to data errors.

In summary, SSDs utilise NAND flash memory to provide fast, reliable, and persistent data storage. They use a combination of techniques, including garbage collection, wear levelling, and error correction, to optimise performance and ensure data integrity.