SanDisk says that its X4 technology will pack four bits of data into each memory cell nearly double  what is currently available.

The company has built the technology with Toshiba using 43-nanometer technology. X4 is going to be built around Secure Digital flash cards that hold 64GB of data. The best on the market are pricey  32GB cards.

In addition to the memory chip, the die also includes an X4 controller and the whole lot will be flogged as an integrated product. Data speeds are about 7.8 megabytes per second which is  comparable to what others are producing at lower bits per cell. 

They will hit the shops in the first half of 2009.