What is a real-time digital system?

A module that performs some pre-defined function

Constrained by the external environment to respond within a fixed time deadline, or to perform its function at some pre-determined rate

(Contrast with most computers, which respond "as quickly as possible")

Often are embedded, meaning that they are a part of a larger system (like an automobile or communications system)

Inputs and outputs are represented digitally (collections of bits), and internal processing shares this representation