The read channel in Flash memory systems degrades over time because the Fowler-Nordheim tunneling used to apply charge to the floating gate eventually compromises the integrity  of the cell because of tunnel oxide degradation.  While degradation is commonly measured in the number of program/erase cycles experienced by a cell, the degradation is proportional to the number of electrons forced into the floating gate and later released by the erasing process.  By managing the amount of charge written to the floating gate to maintain a constant read-channel mutual information, flash lifetime can be extended.