Timer is decremented every clock tick When timer reaches the value 0 an

Timer is decremented every clock tick when timer

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to ensure operating system maintains control. Timer is decremented every clock tick. When timer reaches the value 0, an interrupt occurs. Timer commonly used to implement time sharing. Time also used to compute the current time. Load-timer is a privileged instruction.
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OS Kernel Real work is done in the kernel Users Applications Operating System API, AUI Operating System Kernel Computer Hardware
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Entry Points into Kernel System Call Signal Interrupt Trap
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System Calls User processes must not be given open access to the kernel code The system call interface layer contains entry point in the kernel code Any user or application request that involves access to any system resource must be handled by the kernel code
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Types Of System Calls Process Control File Management Device Management Information maintenance Communications
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  • Virtual memory, Interrupt, Interrupt handler

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