1.4 The Road to the World Beneath the Code

So far, we have looked at the power of chips revealed by the AI era, the kinds of chips responsible for computation and memory, and the many computers around us and the chips inside them. Now we’re ready to take a closer look at what happens inside a computer when code runs. Before getting into the details, let’s first see what this book sets out to connect, and how.

The central question of this book is: “How is code written by people executed inside a computer?” Once you understand how chips store information and compute internally, you can also understand concretely how the instructions contained in code are processed. Connect that to the way chips exchange information and work together, and the process by which an entire computer runs a program begins to come into view. Linking an understanding of chips to the execution of code and the operation of the computer — that is the “world beneath the code” this book explores.

With this perspective in mind, the journey ahead unfolds as follows.

First, we grasp the core of how a computer works, as concepts.

Before diving into complex details, we’ll first sketch the big picture of how a computer operates. The aim is not deep technical explanation but to see the essentials of computer operation as simply and conceptually as possible. It may feel somewhat abstract at first, but this big picture becomes the foundation for understanding why the circuits and components we meet later are needed. Knowing how the computer works as a whole makes it natural to see what role chips and circuits play in executing code.

Second, we climb step by step from hardware toward software.

Explanations of computers usually start with software and work down to hardware. This book takes the opposite direction. Building up step by step from the bottom lets you understand each new structure and behavior on the basis of what came before. Starting from the smallest unit, the transistor, we climb one level at a time: logic circuits, circuits for computation and memory, computer architecture, and finally software. Along the way, we view software as instructions that tell hardware what to do. By carefully examining the basic circuits and the new behaviors that emerge when they are combined, we’ll connect all the way to how hardware carries out a program’s instructions. At the center of this journey is the CPU. As you follow how small circuits create the core operations of a computer through the CPU, you’ll come to understand concretely how software and hardware mesh and work together.

Third, building on that understanding, we step out into the world of real chips.

By this point, following a single CPU will have answered how code is executed. But the world beneath the code is not made of CPUs alone. In the third stage, we broaden that understanding to real-world chips. We’ll look at what the CPU, GPU, and NPU each do well, and why they have different structures depending on their jobs. We’ll also look at how real chips come into being, how the people who make them divide up the work, and which companies make up this world — because the lowest layer of the world beneath the code is, in the end, something someone designed and built. We’ll also see how the structure and role of chips have changed as the demands placed on computers have changed. Through this, we’ll confirm how the fundamental principles learned earlier carry over into real chips and computers.

It may feel like a long journey, but each stage is a solid stepping stone to the next. Even if things feel unfamiliar and difficult at first, as you build up from the fundamentals, a moment will come when the whole picture snaps into focus. Now, let’s begin together with the big picture of how a computer works.