State (computer science)

In computer science and automata theory, the state of a digital logic circuit or computer program is a technical term for all the stored information, at a given instant in time, to which the circuit or program has access. The output of a digital circuit or computer program at any time is completely determined by its current inputs and its state.

Digital logic circuit state

Digital logic circuits can be divided into two types: combinational logic, whose output signals are dependent only on its present input signals, and sequential logic, whose outputs are a function of both the current inputs and the past history of inputs. In sequential logic, information from past inputs is stored in electronic memory elements, such as flip-flops and latches. The stored contents of these memory elements, at a given point in time, is collectively referred to as the circuit's "state" and contains all the information about the past to which the circuit has access.

For example, the state of a microprocessor (computer chip) is the contents of all the memory elements in it: the accumulators, storage registers, data caches, and flags. When computers such as laptops go into a "hibernation" mode to save energy by shutting down the processor, the state of the processor is stored on the computer's disk, so it can be restored when the computer comes out of hibernation, and the processor can take up operations where it left off.