Flash is a non-volatile memory. Flash memory stores information in an array of floating gate transistors, or cells.

NAND memory is a type of Flash memory where all operations are performed per block, similarly to Hard Disk Drives (HDD).

There are generally two types of NAND: Single Level Cell (SLC) and Multi Level Cell (MLC).

The SLC NAND stores 1 bit per each cell.

The MLC NAND stores 2 or 4 bits per cell by using more granular distinction between charge levels of the floating gate. This reduces design margins and leads to more complex implementation. The added complexity allows the increase of data density, hence lower $/GB. However, the MLC NAND pays the price elsewhere. In comparison to the SLC NAND, it achieves in general 50% of lower transfer rates and 10 times lower write endurance. It also yields lower data reliability and has higher power consumption.

MLC NAND lower reliability and endurance implications

Lower reliability of MLC NAND requires the use of the most powerful Error Correction Code (ECC). The wear-leveling is simply mandatory. Today, the overall data reliability is still not sufficient for MLC NAND use in general industrial applications.

The SLC NAND based devices require much less powerful ECC, or wear-leveling capability to achieve adequate data and device reliability.

Applications

The MLC NAND is used therefore in consumer type of products such media players, consumer media cards, and cell phones. There are also first MLC NAND flash SSD implementations. They are designed for the consumer market.

The SLC NAND must be used in the majority of industrial and defense applications to meet professional grade performance and reliability requirements.

Memkor uses SLC NAND for all industrial products

All Memkor SATA, PATA and SCSI products are design for industrial applications and are built with the highest quality SLC NAND.

SLC vs. MLC NAND - Flash SSD perspective