NAND Flash Data Storage Overview - SLC, MLC and TLC

Cactus Technologies discusses the differences between SLC, MLC, and TLC NAND Flash Data Storage.

Comparison of SLC, MLC, and TLC NAND Flash
Comparison of SLC, MLC, and TLC NAND Flash

The NAND flash architecture was introduced by Toshiba in 1989 and by 2000 became the memory choice of the majority for flash data storage industry. Since NAND flash is non-volatile (doesn't require power to maintain its data) it is ideal for storing data in removable or embedded products. Today, almost all Flash Data Storage Devices are based on some form of NAND flash memory.

The reason for NAND flash's ascendance is due to its smaller chip area required to store a given amount of data than previous NOR based memory or SRAM (which requires power to maintain its data). The smaller chip area reduces the cost per bit and allows for larger capacities on a single die.

It takes a large amount of resources to compete in the NAND market and it is dominated by a few key companies: Samsung, Toshiba/SanDisk, Intel/Micron and Hynix. In order to compete effectively, a manufacturer has to produce their memory at the finest trace widths, have the economy of scale of mega-fabs and for lowest cost consumer cards, store as many bits of data as possible in a single cell.

SLC (Single Level Cell) NAND was the original NAND architecture and still is made today due to its much higher endurance over the MLC and TLC NAND discussed later. A SLC NAND cell has only two states - a high or a low. For this reason it's the simplest to set to a certain state and the retrieve the content since it can only be a 0 or 1.

MLC (Multi Level Cell) NAND was invented to double the amount of data stored in the same area of silicon on the wafer. This significantly lowers the cost of storing data on a MLC component versus a SLC part. The tradeoff for the lower cost of MLC NAND is less reliability and 10-20 times less endurance cycles (the number of times you can erase/write to the NAND cell).

TLC (Tri Level Cell) NAND takes the MLC concept one step further. By creating more states in the memory cell, you can effectively store 3 bits per cell. Again, the tradeoff is significantly less endurance/write cycles and less reliability than even the MLC components. See figure below.

The lower cost of TLC is great for the consumer market where writes are limited, but TLC should not be used in any applications running Operating Systems, storing mission critical data or most OEM applications.

MLC NAND can be used in some OEM applications where there are not a significant amount of write cycles. Sending updates to the field, and read only applications are two key areas.

SLC NAND is the only memory which meets all OEM application requirements with high levels of endurance, long life cycles, high reliability and optional wide temperature ranges.

Cactus Technologies has been focused on the Industrial Flash Storage market since its inception in 2005.

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