An operating system is, at its core, just a program. Like the applications we write, it ends up as binary machine instructions executed by the CPU; as computers evolved, this particular program simply took on more special responsibilities. Today we set aside the many functions of an OS and go back to what it is as a program: the first step is to get its first line of code running on a computer.

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Preface

The operating system is the foundational software behind almost everything developers do. Every application we write runs on top of one, and as soon as you need to optimize an application's performance or resource usage, you need to understand how the OS works. The OS is also the entry point to learning low-level computing, and understanding its internals quietly improves the way you write programs.

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