Unix is an operating system. An operating system takes instructions from the user for starting applications and manages the computer resources, including memory, processor, and the file system. Unix, Macintosh Windows and Microsoft Windows are operating systems. Unix (Linux is a version of Unix) and the older DOS are command-line based, whereas Windows are point and click. A command-line operating system gives the user far greater control, so it is the superior tool for computational science and engineering, but it requires some practice to learn. In this course we try to make the learning curve gentle.