Any program is only as good as it is useful- Linus Torvalds. According to the Merriam-Webster dictionary, an operating system is a computer's main program that controls how the computer works and makes other programs work. Linus Torvalds in 1991 prepared the UNIX operating system to be used instead of ms-dos; Windows 95 ran on the best ms-dos. Windows and Linux are different operating systems based on different code systems that create comparatively different security, stability, usability, and communities. Windows 7 starts with Microsoft Security Essentials and Windows Defender. One of the recurring problems with Microsoft Security Essentials is its automatic update feature which sometimes fails to update. However, Microsoft has provided information on how to fix the problem on its website. Microsoft Security Essentials protects your computer from viruses, spyware, and hacker intrusions, but does not provide a firewall or malware protection. The lack of certain protections makes it inferior to other free antiviruses, however it protects your system from most infections and intrusions. Ubuntu, a version of Linux, boots without antivirus because Linux is not as vulnerable to viruses as Windows. The way Linux is built makes it difficult for viruses to run. The only reason anyone would need antivirus on a Linux-based operating system is if they were sending files to a Windows computer or if the Linux computer was on the same network. Ubuntu starts with a default firewall, but it is not enabled by default. Windows is not known for its stability. A key factor in its stability is the infamous blue screen, also called the blue screen of death. Which is a stop error where the computer stops. There is usually some sort of code on the screen that can help you understand the problem. However, the computer is programmed to restart quickly making it difficult to get the error code. The more lines of code something has, the more bugs it will have. Windows 7 has over two million lines of code, which makes the possibility of bugs very high. Ubuntu 12.04 does not have a stop error. Ubuntu also has fewer lines of code which makes it more stable. Drivers are less available for Linux, because some of them are proprietary. The Windows community, the people who help by posting fixes for recurring problems on forums, is not as large as Linux..