Operating system software

The most important item of system software running on any computer is the operating system. Its role is to provide the services and manage the resources so that the user can interact with the hardware. This will include providing the means to enable various applications that are stored on the hard disk of the PC to be run when required. The operating system will also interact with other devices in tasks such as accessing a CD ROM, or a scanner when it is needed for use. Common examples of operating systems that run on a PC are UNIX, Linux, DOS, and Windows XP.

The first generation mainframe operating system software was generally controlled by one job at a time called batch processing. Huge decks of punched cards or reels of paper tape were used to do this, which was extremely slow. Added to that, processing was usually centralized in some company center, thus program submissions would take days to process. As computers became more powerful in terms of speed and memory, so operating system software became more sophisticated, enabling more than one task to be processed at one time. This was known as multiprocessing and made more efficient use of the computer's resources because the operating system could be programmed to control the simultaneous operation of many jobs in the computer. The concept of timesharing quickly followed on both mainframes and minicomputers from the 1970s. Timesharing allowed for several terminal users to be connected to the computer, possible via remote connections, and gain access to the central processing unit through a time slice. This time slice could be allocated to thousands of on-line users simultaneously. However, because of the speed of the computer, the user would not be aware of this and would feel they were getting dedicated service.

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