How do operating systems manage the allocation of CPU resources among multiple running processes?

Operating systems manage CPU resources through sophisticated scheduling algorithms that prioritize processes and threads while balancing various system performance metrics such as throughput, responsiveness, and fairness. These algorithms determine the order in which processes are executed based on criteria such as process priority, arrival time, and resource requirements. Common scheduling algorithms include First-Come, First-Served (FCFS), Shortest Job Next (SJN), Round Robin (RR), and Priority Scheduling, each with its trade-offs in terms of complexity, efficiency, and fairness. For instance, Round Robin, used in time-sharing systems, allocates a fixed time slice to each process in a cyclic order, ensuring fairness but potentially at the cost of increased context-switching overhead.

Different operating systems implement process scheduling with varying emphases on certain criteria. For example, Windows uses a preemptive priority-based scheduling algorithm that assigns a dynamic priority to each thread, allowing the system to respond quickly to interactive tasks while maintaining overall throughput. Linux, on the other hand, employs the Completely Fair Scheduler (CFS), which strives to provide equal CPU time to all processes by maintaining a balanced tree structure to minimize latency, favoring a more equitable distribution of CPU resources among processes. macOS adopts a combination of priority-based preemptive scheduling and a proportional-share model, borrowing from both BSD and Mach microkernel influences, aimed at optimizing both system performance and user experience. Each of these systems tailors its approach to suit its intended use case scenario, whether it be responsiveness in highly interactive environments or fairness and efficiency in server and multi-user environments.