When purchasing dedicated servers, web hosting providers generally allow you to choose an operating system when placing your order for the server, usually on the sign up page after making a selection.
These operating systems are usually Linux, Linux Based or Windows operating systems.
Choosing the correct operating system is important as compatibility with software you intend to use on your server is key and also consider inquiry about whether you will get full root access to your server if you choose to go with Linux Operating System.
If you choose to go with a Linux Dedicated Server Hosting Provider (which 1onlinehost is), you will be able to choose amongst a number of operating systems such as **Debian, CentOS, Ubuntu **and more to that be able to choose a Control Panel such as DirectAdmin which is offered free if you do not intend on doing any technical work with your server.
What type of OS are you planning to install? Most of the server providers will have Windows and Linux pre-installed, which are good enough to perform the task needed.