State is information retained from earlier events. A sequential circuit uses that stored information as well as current inputs. Feedback can make a circuit remember a value by reinforcing one of two stable conditions. Latches and flip-flops are practical storage elements built around controlled state updates.
Worked example
Imagine a one-bit alarm memory. A brief alarm event sets its stored bit to one. After the event disappears, feedback keeps the bit at one until a reset request clears it. A purely combinational output would instead disappear as soon as the input event ended.
What to watch for
Uncontrolled feedback can oscillate or create an unstable condition. Memory behavior requires a defined circuit structure and timing rules, not an arbitrary wire from output to input.
Try it yourself
Why can two identical current input patterns produce different outputs in a sequential circuit?
Answer: The circuits may hold different earlier states. Present input values alone do not describe the complete situation.
How to study this topic
Write the old state, input values and next state in separate columns. Mark the active clock edge or enable interval. This prevents a stored value from being confused with an input that is merely waiting to be captured.
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Digital Electronics