A signal represents a collection of information, and systems are designed to process these input signals to produce meaningful output responses. Linear systems, based on linear operators, provide a simplified and effective way to model and analyze system behavior compared to nonlinear systems. They are widely applied in areas such as control engineering, signal processing, and telecommunications. Systems can be realized through physical components or implemented via algorithms in software. Signal magnitude is typically measured in terms of energy for finite signals, while power is used when energy is infinite. Continuous systems, such as those in analog electronics, work with continuous input and output signals.