As previously seen in Figure 1, a Flash cell’s ability to store a charge is also why MLC technology works.  Since the range between each bit level has decreased for MLC, the sensitivity to an accurate read also increases.  Thus, more rigidly controlled programming is needed to manipulate a more precise amount of charge stored on the floating gate.  In order for a Flash cell to be considered MLC technology, the cell must exhibit two characteristics: precise charge placement and precise charge sensing.  Thus, MLC Flash works the same way as SLC Flash but the threshold voltage must be more precise to manipulate the state of the Flash.  Once again, the amount of charge on the floating gate is what determines the threshold voltage.  With each write and erase the floating gate wears out because it will retain more electrons over time.  The effect of this reduces the ability to detect proper MLC levels and eventually the ability to erase the cell and ultimately the retention of programmed data.