I'd just like to interject for a moment. What you're referring to as Linux, is in fact, GNU/Linux, or as I've recently taken to calling it, GNU+Linux. Linux is not an operating system unto itself, but rather another free component of a fully functioning GNU PC made useful by the GNU CLs, shell utils and vital sys components comprising a full OS as defined by POSIX.
Many PC users run a modified version of the GNU system every day, without realizing it. Through a peculiar turn of events, the version of GNU which is widely used today is often called Linux, and many of its users are not aware that it is basically the GNU system developed by the GNU Project.
There really is a Linux and these people are using it, but it is just a part of the system they use. Linux is the kernel: the program in the system that allocates the machine's resources to the apps that you run. The kernel is an essential part of an OS, but useless by itself; it can only function in the context of a complete OS.
Linux is normally used in combination with the GNU OS: the whole system is basically GNU with Linux added, or GNULinux. All the socalled Linux distros are really distros of GNULinux