What is the difference between SLC and MLC?

SLC and MLC are both NAND-based non-volatile memory technologies.  Multi-Level Cell (MLC) NAND and Single-Level Cell (SLC) NAND offer capabilities that serve two very different types of applications – those requiring high performance at an attractive cost-per-bit and those seeking even higher performance over time, that are less cost-sensitive.

MLC NAND Flash allows each memory cell to store two bits of information, compared to the one bit-per-cell SLC NAND Flash allows.  As a result, 90 nanometer (nm) MLC NAND offers a larger capacity (typically twice the density of SLC) and at a cost point appropriate for consumer products multi-function cell phones, digital cameras, USB drives and memory cards.  Toshiba 90nm MLC NAND Flash is rated to last approximately 10,000 cycles, which is considered more than sufficient for the average consumer application.  For example, a USB drive application that used the 10,000 write/erase cycles would enable the user to completely write and erase the entire contents once per day for 27 years, well beyond the life of the hardware.

Though SLC NAND offers a lower density, it also provides an enhanced level of performance in the form of faster write speeds.  Because SLC stores only one bit per cell, the likelihood for error is reduced. At 90 nanometer process, it is recommended to implement a 1 to 2-bit ECC for SLC, whereas 4-bit ECC is recommended on the MLC architecture. SLC also allows for longer write/erase cycle endurance and has a life expectancy rated at approximately 100,000 cycles, making it a better fit for use in applications requiring higher reliability, increased endurance and viability in multi-year product life cycles.