Flash memory is nothing but the most popularly called USB drive. At the most basic level, flash memory is composed of array of gate transistors called cells.
These cells has two types of gates: NAND and NOR . They are also classified in two ways depending on how they store data, they are single level cells and multi level cells
SLC can store only one bit at a time, while MLC store more than one bit per cell,just by varying the electrical charges. Thus MLC devices will be able to store more data than the SLC devices.
These devices are already in the market, though they cost more than SLC ones.
Multi-level cells are created by stacking cells of the same size, i.e doubling the capacity. This is the type of memory used in iPods. Though, it doubles the capacity, access speeds is reduced.
Now at present flash technology has developed which inserts silicon columns between layers without stacking multiple layers.
