Author: Christian.Queinnec@lip6.fr

## Chapter Overview

The first section indicates how to use the `Unix` module. We will talk about the handling of errors specific to that module and about the portability of system calls to Windows.
The second section presents file descriptors in the Unix sense, and their use for input and output operations of a lower level than those provided by the preloaded module `Pervasives`.
Processes are introduced in the third section. We talk about their creation, their disappearance and about the way in which all processes support their descendence relation in the Unix model.
The fourth section describes the basic means of communications between processes: pipes and signals.
The two last sections will be continued in chapters 19 and 20 by the presentation of lightweight processes and sockets.