Capacitors on silicon chips used as memories can be interpreted as storing a 1 if the capacitor is charged, 0 if uncharged. Alternately, the positioning of the charges (positive on top or negative on top) could be used to encode 1 or 0.

However, charges leak from capacitors so that eventually the two plates neutralize on their own. The smaller the plates the faster they leak. The tiny capacitors that are built on silicon chips are so small that they leak very rapidly, and hence all the 1s and 0s stored in a DRAM memory would evaporate very soon. Therefore, refresh circuitry is built into these memory chips causing each bit to be read every couple milliseconds and stored afresh so that its 1 or 0 is maintained. This adds complexity to the chip and slows it down.