1.0 IntroductionAn operating system (OS) is a software program that manages the hardware and software resources of a computer. The operating system is an essential component of the system software of a computer system. Operating system programs make system resources available to users, to the user's application programs, and to other application programs running on the computer. (After Silberschatz and Gagne et al., 2010) Some operating systems are designed for convenience, others for efficiency, and a combination of both (After Silberschatz and Gagne et al., 2010). The operating system can be found on almost any device containing a computer – from cell phones and video game consoles to supercomputers and servers. Examples of modern operating systems include Android, iOS, Linux, Microsoft Windows, Windows Phone, and IBM z/OS. All of these, except Windows, Windows Phone, and IBM z/OS, share their roots in Unix.1.1 Windows IntroductionMicrosoft Windows is a series of graphical interface operating systems developed, marketed, and sold by Microsoft. Microsoft introduced an operating environment named Windows as a graphical operating system shell for MS-DOS in response to growing interest in graphical user interfaces (GUIs). Microsoft now controls the global personal computer market with more than 90% market share, surpassing Mac OS. (From windows.microsoft.com, 2013)1.2 Unix IntroductionUnix is ​​a multi-tasking, multi-user operating system. Unix is ​​an operating system developed in the 1960s and since then it has been constantly evolving. It is a stable multi-user and multi-tasking system for servers, desktops and laptops. Unix systems also have a graphical user interface (GUI) similar to Micro...... middle of paper ....... 2013. MS-DOS history, description, commands, clones, future perspectives. [online] Available at: http://www.linfo.org/ms-dos.html [Accessed: December 8, 2013].Russinovich, M., Solomon, D. and Solomon, D. 2005. Microsoft Internals Windows. Redmond, Washington: Microsoft Press. Silberschatz, A., Gagne, G., and Galvin, P. 2010. Operating system concepts. Hoboken, NJ: Wiley. Stallings, W. 2012. Operating Systems. Boston, [Mass.]: Pearson.Unix.org. 2013. The UNIX system -- History and timeline -- UNIX history. [online] Available at: http://www.unix.org/what_is_unix/history_timeline.html [Accessed: December 8, 2013]. Verma, A. 2008. Unix and Shell Programming. Bangalore: Firewall Media/Laxmi Publications Pvt. Ltd.. Windows.Microsoft.com. 2013. A History of Windows - Microsoft Windows. [online] Available at: http://windows.microsoft.com/en-us/windows/history#T1=era0 [Accessed: December 8 2013].