An operating system (commonly abbreviated OS and O/S) is the software component of a computer system that is responsible for the management and coordination of activities and the sharing of the resources of the computer.There are three major OS: Microsoft Windows (XP or Vista), Apple Mac OS-X and Linux. Most users have Microsoft one, that can support a huge variety of software and is the one supported by the most companies of games and hardware. Linux and OS-X are a "pre-made" OS package where you get along with the OS, also a large pack of applications. But if you intend to play games, or to buy some particular hardware that supports only Microsoft OS, you must choose the Windows.

By now these are the latest OS:

Windows XP SP3

Windows Vista SP1

and the next Microsoft OS will be:

Windows 7 M1
(that means Mileston 1 test. It is programmed to be released in 2009-10)

Then the Apple os is named:

OS-X 10.5 Leopard (that you can also install on a virtual machine because now it uses Intel's CPU)

And finally the Linux OS: there are hundreds of different distributons of linux, and everyone comes with many software ready to install, and usefull control panel and easy installation.

Linux SuSE

Linux Ubuntu

Linux Mandriva

and so on, I cannot write them all!!!!