Digital systems use discrete numerical values or non-numeric symbols for input, processing, transmission, storage, or display rather than being composed of variable voltage, acoustic field or electromagnetic field.

(DAC) Part of the interface that converts digital numbers from the computer into analog (ordinary) voltages or currents.

(E) The electric field strength is used to represent the forces between electric charges. Electric field strength is defined as the force per unit charge on an infinitesimally small charge at any given point in space. The unit of electric field strength is volt per meter (V/m).

A transformer is an electrical device operating on the principle of mutual induction to change the magnitude of current and voltage.

(W) The SI unit of power.
Definition: 1 watt is equal to a power rate of one joule of work per second of time or in electrical terms it is the power produced by a current of one ampere flowing through an electric potential of one volt.
Power is the rate at which work is done, or the rate at which energy is expended and is used both in mechanics and in electricity.
The unit is named for James Watt, a British engineer.