On the surface, Linux seems to be UNIX-like in that it is a file-based OS with a scripting shell interface; however, its source code does not descend from the original UNIX. In 1991, Linus Torvalds, a Finnish university student, began the Linux kernel as a hobby. Torvalds originally used Minix, a simplified UNIX-like system built for teaching operating system design, on his home computer. Minix’s author, Andrew Tanenbaum, did not allow others to extend his operating system, which led Torvalds to create a replacement for Minix.

Also different from UNIX is Linux’s delivery model. Linux distributors range from individuals to informal teams to commercial organizations, each creating its own unique Linux distributions. Today, over 300 different distributions are actively developed*. While some distributors offer support for a cost, others offer none at all, and with each distributor the level of development and testing rigor varies greatly.

*http://lwn.net/Distributions/