Linux is a (usually) free, open source version of the UNIX operating system, created originally in 1991 by a Finn, Linus Torvalds as a college project when he as studying at Helsinki University. It has developed a lot since then and can be used to replace Microsoft Windows completely. In some circumstances, an open source operating system such as Linux can perform much better than Windows, for example, on web servers. DEOSS runs on a Linux, not a Windows server. Whilst this decision was made partly due to cost, the main reason was robustness. More info about Linux: http://www.linux.org/