A form of volatile semiconductor memory in which stored information is degraded with time. The most common example is dynamic RAM (usually abbreviated to DRAM) where the logic state to be entered in each cell is stored as a voltage on the small capacitance associated with the gate of the MOS output transistor for the cell. The voltage decays away with time because of leakage currents in the cell, and so it must be refreshed (i.e. recharged) periodically by external circuitry.