A Linux distribution is a Unix-like operating system. Distributions (often called distros for short) consist of a large collection of software applications such as word processors, spreadsheets, media players and graphics applications. The operating system consist of the Linux kernel and a set of libraries and utilities from the GNU project, with graphics support from the X Window System.
Linux distributions takes a wide variety of forms from fully featured desktop and server operating systems to minimal environments. Some distributions are commercially backed distributions, such as Fedora (Red Hat), openSUSE (Novell), Ubuntu (Canonical Ltd.), while others such as Mandriva, Debian, Archlinux and Gentoo are entirely community-driven distributions, though there are other distributions that are driven neither by a corporation nor a community, most famously know is the Slackware distribution.
The leading distributions has been around for a while and are well-established. They are well known in the world of Linux and most of them support several architectures from low-end x86 versions to high-end version for mainframes.
Derived Linux distributions are products that has been build upon or based upon other Linux distributions. One such distribution is the very popular and commercially sponsored Ubuntu distribution that has been derived from Debian. Actually Ubuntu is continuously derived from Debian, and without Debian Ubuntu wouldn't exist.
While the non-derived distributions has been developed with great consideration as to what kind of hardware to support and what kind of features to offer, the derived distributions are often nothing more than "hacks" and "tweaks" to the original work of the non-derived distributions.
"Hacks" and "tweaks" to make the derived distribution serve a specific purpose, as in the case with Ubuntu that could be considered as nothing more than a commercialized and patched version of Debian (running Debian's unstable branch).
One of the major problems with most derived distributions is that even thought they often provide some nice custom developed tools (in most cases nothing more than GUI applications), they also remove features that are essential to running a stable Linux system.
They often change fundamental aspects of the system for no apparent reason. One example is when they move configuration files to places not commonly used, causing frustration to Linux administrators. Sometimes they leave the configuration files in place, but disable them and then use some other custom made configuration file (located in some strange place) controlled by their GUI tool.
Often kernel specific modules are removed leaving the derived distribution a poor choice if you need to add modules to your running kernel. An example is Ubuntu removing the cpufreq modules from the generic kernel that are needed to influence the CPU frequency making laptops save power.
Second generation derived distributions (distributions that are derived from other derived distributions) not only suffer from the same problems, but often make things even worse.
It is well known (or maybe it actually isn't) that Debian has one of the best package management system in the world, making it one of the easiest distributions to keep updated.
Many of the Debian derived distributions want to run with the latest bleeding edge software, and in order to do so they patch the unstable packages from Debian, leaving the system almost impossible to upgrade, when a new release is presented. Users trying to upgrade their system are often left with a broken operating system and the only possible solution to re-install everything from scratch, as is often the case with Ubuntu, Linux Mint and several other derived distributions.
Ubuntu has a new release at each 6 month at a fixed date. This means that they import new applications and packages at the beginning of the period and then spend the rest of the time testing those packages and closing bugs. This also means that by the time the next release is announced, the distribution is already old, and the only updates for the next 6 months will be security updates. This also has the effect that a lot of Ubuntu users re-install each 6 months because they have troubles updating their system.
If you are looking for some fun on the desktop many of the derived distributions are great, but if you are looking for a stable system that you can keep upgraded without re-installing, and if you want to expand your knowledge about Linux, then derived distributions are better left alone.
Another problem with several of the derived distributions, one that I have witnessed many times, is that many of them often has a lot of errors. Many of the derived distributions are actually build with custom made tools to be more appealing to Microsoft Windows users, and while I am sure that many find such tools and efforts nice, the effort should rather be spend on making the non-derived distributions better and more appealing.
Most of the derived distributions that I have tested over the years, and I usually re-test new versions from time to time, has always left me with a poor impression. Whenever someone needs a new Linux distribution I always end up recommending one of the leading independent distributions, and while it might take me a little bit longer to get everything up and running, the user is left with a very stable and very well structured system.
In the rare cases where I have compromised and left the user with a derived distribution, I can always count on the fact, that not far out in the future, I have have to come back and do a re-install.
If you have just arrived from the world of Microsoft Windows, and want to try out Linux, take a look at one of the derived distributions such as Linux Mint. If you like Linux and want to use it as your operating system of choice, then spend a little time learning new stuff and pick one of the independent Linux distributions such as Arch Linux, Debian GNU/Linux, Fedora, OpenSuse or something else.
If you have any comments or corrections feel free to email them to me.