1. If the input to the system is bounded, then the output of the system will also be bounded, or the
impulse response of the system will go to zero in a finite number of steps.
2. An unstable system is one where the output of the system will grow without bound due to any
bounded input, initial condition, or noise, or the impulse response will grow without bound.
3. The impulse response of a marginally stable system stays at a constant level or oscillates between
two finite values.