An operating system is composed of two major parts; these parts are known as the "kernel" and the "userland".

The kernel is responsible for handling communication between the physical hardware and the software running on the machine.

The "userland" is comprised of system utilities and user applications. These include editors, compilers and server daemons. System utilities allowing you to maintain, monitor and even upgrade your system are also included.

The phrase "Linux operating system" is a misnomer, as Linux is a kernel, and requires additional software in order to make it an operating system.

A Linux distribution is comprised of the Linux kernel, and a collection of "userland" software. The software is usually provided by the FSF^[23] and GNU^[24] organisations, as well as many private individuals. Some of it even originates from UCB's^[25] BSD^[26] Unix operating system.

Some commercial Linux distributions even include commercially developed software, often unique to that particular distribution. An example of this would be SuSE Linux's "Openexchange" Server™.

There are many Linux distributions that are available. All of them use the Linux kernel, but they usually differ in what software is available as part of the "userland" how that software is managed and packaged.

Unlike most Unix operating systems, which are based on previous versions of Unix, ultimately all leading back to the original "Unix System" from Bell Labs, the Linux kernel was written from scratch. However, Linux based operating systems follow and implement the Unix paradigm closely enough, that the bulk of this section of the course would apply to both Linux and Unix variants.