# What Are Digital Systems? Put in the most simplistic way possible, digital systems are about signals moving in choreography to fulfill a need. Of course, digital systems are a bit less abstract and less romantic than that. What are these _signals_ anyway? One would be mentally wired (heh) to say that signals are "binary" or "two-valued" sequences of bits coming from somewhere or going somewhere. After all, computers are involved here, so they must be binary signals, right? Not exactly. We will see later on that high-speed digital systems may use signals that are not only two-valued, and we will see the reason why. We will analyze how signals propagate through different media and the problems and impediments they face as they go. We will also slowly rise in the system hierarchy, from the very bottom—electrons, holes, and ions in semiconductors—all the way to the top, where system software, virtualization, and data centers materialize. ==Digital systems are, at the end of the day, a hierarchical arrangement of networked containers, components, and subsystems organized to perform a given function. And the key lies in both its hierarchy and its interconnection: depending on where you stand, a digital system might look very different.== In this text, a _system_ is analyzed as a collection of entities linked using interconnects. Said entities may have one or more internal levels of hierarchy, and the interconnects can be of any physical kind, although we will strictly focus on electric and optical interconnects. Through these interconnects, data shall be transferred. In the text, we will explore in detail each one of these systemic building blocks: the entities and the interfaces that link them together; i.e.; the interconnects. Now, you can either continue by exploring the human side of [[Engineering is Broken (and someone has to fix it)|engineering complex systems]]. Or you can stay on the technical tracks and continue by exploring the [[Hierarchy of Digital Systems (Start Here)|hierarchical nature of digital systems]].