Most of my readers are probably firmly in the Microsoft Windows world when it comes to using a computer. What is Microsoft (MS) Windows (in any one of its many incarnations, whose most common and recent members are Windows XP, Windows Vista and Windows 7)? It's the operating system (OS) of the computer - for most people computers aren't very usable without an operating system. The operating system sits on top of the hardware and provides the complete logic for everything you see when running a computer - it connects to and registers various hardware devices while booting, like graphics card, sound card, mouse and monitor, and provides functions like user management, a graphical user interface (GUI), process management, and much more. The operating system does not include things like web browsers, mail programs or office suite programs (yes, there are alternatives to MS Office, see OpenOffice ). There are many other operating systems, some with restricted niche usage ( RISC