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A ready queue or run queue is used in computer scheduling. Modern computers are capable of running many different programs or processes at the same time. However, the CPU is only capable of handling one process at a time. Processes that are ready for the CPU are kept in a queue for "ready" processes. Other processes that are waiting for an ...
A process that is ready to run but waiting for the CPU can be considered blocked. A priority scheduling algorithm can leave some low-priority processes waiting indefinitely. A steady stream of higher-priority processes can prevent a low-priority process from ever getting the CPU. [1]
minimizing wait time (time from work becoming ready until the first point it begins execution); minimizing latency or response time (time from work becoming ready until it is finished in case of batch activity, [1] [2] [3] or until the system responds and hands the first output to the user in case of interactive activity); [4]
Separate processes into multiple ready queues based on their need for the processor. Give preference to processes with short CPU bursts. Give preference to processes with high I/O bursts. (I/O bound processes will sleep in the wait queue to give other processes CPU time.) The multilevel feedback queue was first developed by Fernando J. Corbató ...
Processes are also removed from the run queue when they ask to sleep, are waiting on a resource to become available, or have been terminated. In the Linux operating system (prior to kernel 2.6.23), each CPU in the system is given a run queue, which maintains both an active and expired array of processes.
For the portion of the time required for CPU cycles, the process is being executed and is occupying the CPU. During the time required for I/O cycles, the process is not using the processor. Instead, it is either waiting to perform Input/Output, or is actually performing Input/Output. An example of this is reading from or writing to a file on disk.
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Some second-level CPU caches run slower than the processor core. When the processor needs to access external memory, it starts placing the address of the requested information on the address bus. It then must wait for the answer, that may come back tens if not hundreds of cycles later. Each of the cycles spent waiting is called a wait state.