1.1 Introduction
All operating systems provide services for programs they run. Typical services include
executing a new program, opening a file, reading a file, allocating a region of memory,
getting the current time of day, and so on. The focus of this text is to describe the
services provided by various versions of the UNIX operating system.
Describing the UNIX System in a strictly linear fashion, without any forward
references to terms that haven’t been described yet, is nearly impossible