The program Linux is an operating system that that enables applications and the computer operator to access the devices on the computer to perform desired functions. Linus Torvald's created Linux on September 1st, 2001.
Linux is freely available, and no one is required to register their copies with any central authority, so it is difficult to know how many people use Linux. Several businesses now survive solely on selling and supporting Linux.
Windows is a general applications OS, targeted largely at businesses. It has a very wide range of applications, many of which can be downloaded and run for free. It is notorious for the number of security holes it has, and has amazingly bad tech support.
MacOS is the operating system for Apple computers. It has a highly polished user interface, takes very little effort to use, and has decent tech support.
Linux is the most popular attempt to create a Unix-like operating system for personal computers. Until recently, Linux also had all of the limitations of Unix, with the sole benefit that you could run it on an Intel based PC.
Linux is less vulnerable to viruses and is easy to install and stable.
However many windows apps will not run through Linux and it's a learning curve for new people.
http://www.linux.com/learn/new-user-guides/376-linux-is-everywhere-an-overview-of-the-linux-operating-system
http://www.livinginternet.com/i/iw_unix_gnulinux.htm
http://www.renewablepcs.com/about-linux/advantages-of-using-Linux
