When an input signal is applied to most devices or circuits, the output somehow changes in response to the input , and when the input signal is removed, the output returns to its original state. These circuits do not exhibit the property of memory, since their outputs revert back to normal. When an input is applied to such a circuit, the output will change its state, but it will remain in the new state even after the input is removed. This property of retaining its response to a momentary input is called memory. Figure 1-10 illustrates nonmemory operations.
Memory devices and circuits play an important role in digital systems because they provide means for storing binary numbers either temporarily or permanently, with the ability to change the stored information at any time. As we shall see, the various memory elements include magnetic types and those which utilize electronic latching circuits (called latches and flip-flops)