In computing, an operating system (OS) is the system software responsible for the direct control and management of hardware and basic system operations. Additionally, it provides a foundation upon which to run application software such as word processing programs and web browsers.
Today's operating systems
As of 2005, the major operating systems in widespread use on general-purpose computers (including personal computers) have consolidated into two main families: the Unix-like family and the Microsoft Windows family. Mainframe computers and embedded systems use a variety of different operating systems, many with no direct connection to Windows or Unix.
The Unix-like family is a more diverse group of operating systems, with several major sub-categories including System V, BSD, and Linux. The name "Unix" is a trademark of The Open Group which licenses it for use to any operating system that has been shown to conform to the definitions that they have cooperatively developed. The name is commonly used to refer to the large set of operating systems which resemble the original Unix. Unix systems run on a wide variety of machine architectures. Unix systems are used heavily as server systems in business, as well as workstations in academic and engineering environments. Free software Unix variants, such as Linux and BSD are increasingly popular, and have made inroads on the desktop market as well. Some proprietary Unix variants like HP's HP-UX and IBM's AIX are designed to run only on that vendor's proprietary hardware while others can run on the vendor's proprietary hardware and also on industry-standard PCs. Sun's formerly proprietary Solaris (it is becoming open-source under the CDDL license) is one such versatile but true Unix (it can run on Sun's servers but also on smaller x86 systems). Apple's Mac OS X, a BSD variant, has replaced Apple's earlier (non-Unix) Mac OS in a small but dedicated market, becoming one of the most popular Unix systems in the process.
The Microsoft Windows family of operating systems originated as a graphical layer on top of the older MS-DOS environment for the IBM PC. Modern versions are based on the newer Windows NT core that first took shape in OS/2. Windows runs on 32- and 64-bit Intel and AMD computers, although earlier versions also ran on the DEC Alpha, MIPS and PowerPC architectures (and there was work in progress to make it work also on the SPARC architecture). Today, Windows is a popular desktop operating system, enjoying a near-monopoly of around 90% of the worldwide desktop market share. It is also widely used on low-end and mid-range servers, supporting applications such as Web servers and database servers.
Common operating systems
- Operating system @ dmoz.org
- TUNES wiki, contains reviews of operating systems
- Multicians.org and the History of Operating Systems
- Operating System - explains what an operating system is and provides various examples
- The "Write Your Own Operating System" OS Developer FAQ
- How OSs Work
- Operating System Programming- Tutorials and source code
- Operating Systems Technical Comparison
- BonaFide OS Development - resource for operating system developers