Electronics deals with the generation, distribution, control and application of electromagnetism. This distinction started around 1900s with the developments of various non-mechanical device.
Analog electronics are constructed from combinations of circuits. Analog circuits use a continuous range of voltage as opposed to discrete levels as in digital circuits. The number of different analog circuits so far devised is huge, especially because a 'circuit' can be defined as anything from a single component, to systems containing thousands of components. Analog circuits can be linear circuits although non-linear effects are in analog circuits. Analog circuitry can use digital or microprocessor techniques to improve performance ("mixed signal") rather than analog or digital. Sometimes it may be difficult to differentiate between analog and digital circuits as they have elements of both linear and non-linear operation.
Digital electronics are circuits based on a number of discrete voltage levels. Digital circuits are the most common physical representation of Boolean algebra and are the basis of all digital computers. The terms "digital circuit", "digital system" and "logic" are interchangeable in the context of digital circuits. Digital circuits use two voltage levels labeled "Low"(0) [off] and "High"(1) [0n]. Often "Low" will be near zero volts and "High" will be at a higher level depending on the supply voltage in use. Ternary (with three states) logic has been studied, and some prototype computers made.