A DRAM is made with cells that store data as charge on capacitors. The presence or absence of charge in a capacitor is interpreted as binary 1 or 0.
Because capacitors have a natural tendency to discharge due to leakage current, dynamic RAM require periodic charge refreshing to maintain data storage. The term dynamic refers to this tendency of the stored charge to leak away, even with power continuously applied.
A typical DRAM structure for an individual cell that stores one bit information is shown in the figure 3.3.
Figure 3.3: Dynamic RAM (DRAM) cell