SanDisk is now producing Flash memory cards with four bits of data in each memory cell — twice as many as in conventional multi-level cell (MLC) NAND (2-bits-per-cell) memory chips. With X4 technology, the 64GB NAND Flash chip is the highest-density single-die memory device on the market. SanDisk is currently producing 8GB and 16GB SDHC cards as well as 8GB and 16GB Memory Stick PRO Duo cards using X4 technology.