Every program is as good as it is useful- Linus Torvalds. According to the Merriam-Webster dictionary, an operating system is the main program on a computer that controls the operation of the computer and allows other programs to operate. Linus Torvalds organized in 1991 the use of the UNIX operating system instead of ms-dos; Windows 95 was run on MS-DOS. Windows and Linux are different operating systems built from different code systems, making security, stability, usability, and communities relatively different. Windows 7 starts with Microsoft Security Essentials and Windows Defender. One of the recurring problems with Microsoft Security Essentials is its auto-update feature, sometimes it doesn't update. However, Microsoft has provided information on how to resolve the issue on its website. Microsoft Security Essentials protects your computer against viruses, spyware, and hacker intrusions, but it does not provide firewall or malware protection. The lack of certain protections makes it inferior to other free antiviruses, however, it protects the system from the majority of 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 you are sending files to a Windows computer or if the Linux computer is on the same network. Ubuntu boots with a predefined firewall, but it is not enabled by default. Windows is not known for its stability. A key factor in its stability is the famous blue screen, also called the blue screen of death. This is a Stop error when the computer shuts down. Usually, some sort of code will appear on the screen that can help you fix the problem. However, the computer is programmed to restart quickly, making it difficult to get this error code. The more lines of code something contains, the more bugs it will have. Windows 7 contains over two million lines of code, making the risk of bugs very high. Ubuntu 12.04 does not have a STOP error. Ubuntu also has fewer lines of code, making it more stable. Drivers are less available for Linux, as some of them are proprietary. The Windows community, people who help by posting fixes for recurring issues on the forums, doesn't have the scale of Linux..