The Microsoft Windows operating system is developed and released by a single company. It comes with a minimal set of applications (a calculator, a few games, some networking tools, an Internet browser.. etc). Other software can be obtained by users from various sources and installed on the operating system.
GNU/Linux is different. A GNU/Linux operating system is made of a Linux kernel, a set of GNU tools, an installation program, a package management system and a lot of other software components. Because all these components are free to use and to distribute, anybody can assemble and configure them according to their needs and create their very own GNU/Linux operating system. Since 1993, a lot of people and companies have been distributing Linux operating systems. These distributions made it easy for people to get and to install a working GNU/Linux system on their personal computer.
At first only a few distributions were available. Nowadays there are so many, that it would be pointless to compare all of them. The website http://www.distrowatch.com lists more than 350 active distributions and reports new releases almost every day. Of course, some distributions are quite similar, although some others are very different to each others. Depending on your needs you'll prefer some more than others.
All distributions include the Linux kernel developed by Linus Torvalds and the GNU tools developed by Richard Stallman but they don't necessarily use their latest versions. Some distributions even make their own changes to the kernel. Distributions usually differ in the choice of software applications they offer, in the way these software applications are configured and in the way they are installed and upgraded. Distributions also differ in many aspects such as their philosophy towards proprietary software, their priorities between ease of use and efficiency or between stability and latest technology. In fact, every distribution is different and this means you have more than 350 ways to run GNU/Linux!
Of course some distributions are more popular than others. This article is dedicated to the 10 most famous and popular: Debian, Slackware, Fedora, Mandriva, Suse, Ubuntu, Knoppix, Gentoo, Mepis and Xandros.