SanDisk is shipping memory chips that will allow consumers to store more data on tiny Secure Digital flash cards.

The Milpitas, Calif., company's X4 technology packs four bits of data into each memory cell. To date, flash memory chipmakers typically stored one bit or two bits per cell. Each individual die--or chip--holds 64 gigabits of data, or 8 gigabytes. This is the highest capacity per die in the industry, according to SanDisk.

The technology is not yet shipping in cutting-edge retail products, however: it is currently being used in 8GB and 16GB SDHC (Secure Digital High Capacity) cards as well as 8GB and 16GB Memory Stick PRO Duo cards, the company said.

Future related technology from SanDisk--possibly not based on current X4--is expected to yield SD flash cards that hold 64GB of data and larger capacities. Currently, mainstream SanDisk SD cards top out at 32GB.

Flash memory cards sold at retailers are typically not as reliable as solid-state drives--which also use flash chips--sold with laptops. And the higher the density per chip and the more bits per cell, the bigger the challenge for maintaining data reliability. SanDisk says it has met this challenge.