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operating systemThe master control program that runs the computer. It is the first program loaded when the computer is turned on, and its main part, called the kernel, resides in memory at all times. The operating system performs 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. The operating system acts as an interface between the user and the computer, enabling the user to operate software applications and access all resources available on the computer, including the CPU, media drives, memory, printers, and storage devices.