Analog voltage storage times are limited since the charge on a capacitor will eventually leak away. The problem of discrete storage reduces to the need to store a large number of two-state variables. The four commonly used methods are: 1) magnetic domain orientation, 2) presence or absence of charge (not amount of charge) on a capacitor, 3) presence or absence of an electrical connection and 4) the DC current path through the latches and flip-flops of a digital circuit. We will discuss only the latter.