In science, technology, business, and, in fact, most other fields of endeavour, we are constantly dealing with quantities. Quantities are measured, monitored, recorded, manipulated arithmetically, observed, or in some other way utilized in most physical systems. It is important when dealing with various quantities that we be able to represent their values efficiently and accurately. There are basically two ways of representing the numerical value of quantities: analog and digital.
Analog Representation
In analog representation a quantity is represented by a voltage, current,
or meter movement that is proportional to the value of that quantity.
Analog quantities such as those cited above have an important
characteristic: they can vary over a continuous range of values.
Below is a diagram of analog voltage vs time:
Digital Representation
In digital representation the quantities are represented not by
proportional quantities but by symbols called digits. As an example,
consider the digital watch, which provides the time of day in the form
of decimal digits which represent hours and minutes (and sometimes
seconds). As we know, the time of day changes continuously, but the
digital watch reading does not change continuously; rather, it changes
in steps of one per minute (or per second). In other words, this digital
representation of the time of day changes in discrete steps, as
compared with the representation of time provided by an analog
watch, where the dial reading changes continuously.
Below is a diagram of digital voltage vs time:
The major difference between analog and digital quantities, then, can be simply stated as follows:
Analog = continuous
Digital = discrete (step by step)
