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operating system Last modified: Friday, January 04, 2002
The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers. For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system. Operating systems can be classified as follows: multi-user : Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users. multiprocessing : Supports running a program on more than one CPU. multitasking : Allows more than one program to run concurrently. multithreading : Allows different parts of a single program to run concurrently. real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time. Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux. As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.
Virtual Doctor  Using the Virtual Doctor, users can acquire help with a specific problem, download software, grab updates for their operating system or receive expert tutorials catering to their specific needs. DOS concepts and functions  This page is for novice computer users and provides a short introduction to computers and basic functions of an operating system. A table of contents then provides links to specific DOS concepts and functions. ACM SIG Operating Systems Addresses a broad spectrum of issues associated with operating systems research and development. CMX-RTX real time operating system Product feature page for the CMS-RTX real time multitasking operating system for microprocessors and microcomputers. OS News On-line magazine covering alternative operating systems and computing environments. osOpinion Daily computer and operating system news and opinion commentary. Real-Time and RTOS Computing Resources List of sites related to real time operating systems and programming. RTMX operating system information page Provides product information for the RTMX real time operating system, including features and supported CPU types. In addition, there are links to related real time computing Web sites. Yahoo!'s operating systems page Yahoo!'s directory of links to operating systems. Yahoo!'s OS/2 operating system page Yahoo!'s directory of the OS/2 operating system. Yahoo!'s real time systems page Yahoo!'s directory of real time systems. Yahoo!'s UNIX page Yahoo!'s directory of UNIX operating systems links.	Related Categories Operating Systems Related Terms abort application BeOS BIOS command processor DOS fatal exception error file management system flat file system kernel kernel32.dll Mac OS Microsoft Windows multiprocessing multitasking multithreading multi-user MVS NTLDR OS/2 PXE UNIX VMS Windows 2000 Windows CE Windows XP