Transmitting information from one place to another has always been of great interest to humankind. Before the discovery of electricity and the invention of electronic devices, the principal means for transmitting information were limited to sound, writing and printing, and light. Since the discovery of electricity, transmitting information with electrical signals through wires and with electromagnetic waves through the air have come to dominate information technology.

Most electronic transmission of information makes use of a very limited symbol set—usually binary numbers consisting of groups of binary digits (0s and 1s). An electrical current or a magnetic field can very easily be interpreted as being either on or off, or in one direction or the other, and so is well suited to representing binary digits.

Binary numbers are the building blocks of digital technology. To put digital signals into context, we must first understand...