19. Introduction

The power of Unix comes from the fundamental idea that everything is a file or really more accurately a stream. However, in many cases we want to store data persistently on disks and in that case file systems provide that abstraction, and, as we will see, a richer set of abstractions.

We first describe this rich interface Unix (and many similar systems) require of file systems. We then discuss the ugly hardware abstractions that needs to be transformed by file systems into this interface. We then discuss how file systems are implemented.