Linux is an open source operating system (OS) that presents you with many choices for your dedicated server. Because it's open source, many different companies have created their own versions, or "distributions" of the software.
The upside of open source software is that it is typically available for free, but the downside is that if you're not well-versed in operating systems, you have no guarantees or ways to fix problems. That's why companies have been able to take the open source kernel, develop their own distribution of it and charge a subscription or fee for people using their OS. While the company may charge a fee, it must provide a copy of the code to any buyers and cannot copyright the code.
Most Web hosts offer some or all of the following distributions to dedicated hosting customers.
Distributions
Commonly referred to as "distros" here are several options for your Linux-based operating system:
Red Hat Enterprise Linux — Red Hat is one of the most popular Linux distributions for dedicated servers. Red Hat Inc. targets this version of the operating system to the commercial market and large enterprises. It offers thousands of applications, many deployment options and a range of operating systems from some of the leading hardware vendors.
Fedora — Based on Red Hat, the Fedora operating system is always free for anyone to use, modify and distribute. It was developed by the Fedora project, which is open to anyone, and remains a true open source operating system today. New releases of this platform come out twice a year.
Ubuntu — Another community-developed operating system, Ubuntu is available to anyone free of charge. The company that releases new Ubuntu distributions every six months makes its money by charging for support. Based on Debian, the Ubuntu Server Edition is energy efficient with low memory and disk footprint usage.
CentOS — Based on Red Hat, CentOS is an enterprise Linux distribution offered for free.
FreeBSD — This operating system is actually more similar to UNIX than Linux. It has many of the same features UNIX offers, but it's open source.
Now that you have a good overview of the Linux operating system for dedicated servers, take a look at the other most popular operating system: Windows.