DRAM – Dynamic Random Access Memory – composed from cells in a solid state array which can have a positive or negative charge, signalling binary one or zero values. The charge, stored in a capacitor, has to be constantly refreshed by electricity , and it is lost when the power is switched off; hence it is dynamic or volatile. The cells can be individually addressed – randomly addressed – as opposed to stored locations on a tape which have to be serially addressed as the tape streams through a drive.

DRAM consists of billions of cells laid out in a square array. Each cell needs a transistor, a source with a bit line connection, a gate with a word line connection, a capacitor to store charge, and a drain. The capacitor is above the drain.

A bit is stored with the presence or absence of charge in a capacitor.

The transistor is used to charge or discharge the capacitor. The word line is used to switch the cell on or off and the bit line is for reading and writing data.