The low-level operating system, handling files, disks, networking, and other necessities we take for granted. Most users rarely notice the kernel.

Thousands of programs for file manipulation, text editing, mathematics, web browsing, audio, video, computer programming, typesetting, encryption, DVD burning…you name it.

A user interface for typing commands, executing them, and displaying the results. Linux has various shells: the Bourne shell, Korn shell, C shell, and others. This book focuses on bash, the Bourne-Again Shell, which is often the default for user accounts. However, all these shells have similar basic functions.

A graphical system that provides windows, menus, icons, mouse support, and other familiar GUI elements. More complex graphical environments are built on X; the most popular are KDE and GNOME. We’ll discuss a few programs that open X windows to run.