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Round-robin is the simplest scheduling algorithm for processes in an operating system, which assigns time slices to each process in equal portions and order, handling all processes have the same priority. In prioritized scheduling systems, processes on an equal priority are often addressed in a round-robin manner. This algorithm starts at the beginning of the list of PDBs (Process Descriptor Block), giving each application in turn a chance at the CPU when time slices become available. Round robin has the great advantage of the fact that it is easy to implement in software. Since the operating system must have a reference to the start of the list, and a reference to the current application, it can easily decide who to run next—just follow the array or chain of PDBs to the next element, and if you reach the end of the array or list, reset back to the start. The PDBs must be checked to ensure that we don’t inadvertently execute a blocked application, as that needlessly could waste CPU time, or worse, make a task think it has found its resources when in reality it should be waiting a while longer.
The word comes from the round-robin principle known from other fields, where each person takes an equal share of something in turn.
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