White Paper: Implementing MLC NAND Flash for Cost-Effective, High-Capacity Memory

Introduction Multi-Level Cell (MLC) technology greatly reduces flash die size to achieve a breakthrough cost structure. It does this by storing 2 bits of data per physical cell instead of the traditional 1 bit per cell, using Binary flash technology. But the increased density of the MLC flash media has grave consequences in terms of data reliability and performance. A number of flash vendors, with varying degrees of success, have made attempts to implement MLC technology on selected flash platforms while overcoming its limitations. Recently, Toshiba introduced MLC NAND technology. Although NAND constitutes a particularly good building block for MLC technology due to its high erase and write performance and high density (small size), MLC NAND is practically unusable for local data and code storage due to the degradation in data reliability and performance. x2 technology, implemented in M-Systems' DiskOnChip G3, combines advanced hardware features and customized software algorithms to boost reliability and performance levels to rival and even exceed those of 1 bit per cell devices. This paper discusses the MLC solutions available on the market today, their benefits and limitations, and the hardware and software innovations of x2 technology that overcome MLC NAND limitations. It concludes with a discussion of how the combination of MLC and x2 technologies is enabling M-Systems' Mobile DiskOnChip® G3 flash disk to function as the most cost-effective, fast and reliable memory solution in mobile handsets and connected devices available on the market today.