When we talk about systems in the most general sense, we are talking about anything that takes in a certain number of inputs and produces a certain number of outputs based on those inputs.

Generalized System |
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In the figure above, the

There are two basic divisions of systems: static and dynamic. In a static system, the current outputs are based solely on the instantaneous values of the current inputs. An example of a static system is a resistor hooked up to a current source:

Resistor connected to a current source |
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At any given moment, the voltage across the resistor (the
output) depends only on the value of the current running
through
it (the input). The current at any time

Simple capacitor connected to a current source |
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Solving for the voltage in the current voltage relationship above, we have:

So in the case of the capacitor, the output voltage depends on the history of the current flowing through it. In a sense, this system has memory. When a system depends on the present and past input, it is said to be a dynamical system.