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 (and would probably be boring). This chapter provides a whirlwind tour of the UNIX System from a programmer's perspective. We'll give some brief descriptions and examples of terms and concepts that appear throughout the text. We describe these features in much more detail in later chapters. This chapter also provides an introduction and overview of the services provided by the UNIX System, for programmers new to this environment.